What is the microbiology of dairy products. Microbiology of dairy products

Raw milk, even under hygienic conditions for its production, usually contains a certain amount of bacteria. If sanitary and hygienic conditions are not observed, milk can be abundantly infected with microbes located on the surface of the udder, falling from the teat canal, from the hands of milkers, milking equipment and utensils, from the air, etc. According to the All-Russian Scientific Research Dairy Institute, in the combined milk, selected directly from farms, the total number of bacteria ranges from 4.6 10 4 to 1.2 - 10 6 in 1 cm3.

The microflora of fresh raw milk is diverse. It contains bacteria lactic acid, butyric, groups of Escherichia coli, putrefactive and enterococci, as well as yeast. Among them, there are microorganisms that can cause a change in protein substances and milk fat, its color (blue, redness), and consistency. There may also be pathogens of various infectious diseases (dysentery, brucellosis, tuberculosis, foot and mouth disease) and food poisoning (Staphylococcus aureus, Salmonella, Listeria, Yersinia).

When storing milk, the number of microorganisms contained in it and the ratio between their individual species change. The nature of these changes depends on the temperature and duration of storage of milk before consumption or processing.

Freshly milked milk contains antimicrobial substances lactenins, lysozymes, etc., which in the first hours after milking delay the development of bacteria in milk and even cause the death of some of them. The period of time during which the antimicrobial properties of milk are preserved is called bactericidal phase. The bactericidal activity of milk decreases with time and the faster, the more bacteria there are in milk and the higher its temperature.

Freshly milked milk has a temperature of about 35 "C. At 30 ° C, the bactericidal phase of milk with a small initial contamination lasts up to 3 hours, at 10 ° C - up to 20, at 5 ° C - up to 36, at 0 "C 48 hours. At one and the same temperature of aging milk with an initial bacterial contamination of 104 in 1 cm3, the bactericidal phase at 3-5 ° C lasts 24 hours or more, and with a content of 106 bacteria in 1 cm3 - only 3-6 hours (N. S. Koroleva and V. F. Semenikhina). To lengthen the bactericidal phase, the milk must be cooled as quickly as possible.

At the end of the bactericidal phase, the reproduction of bacteria begins, and it proceeds the faster, the higher the temperature of storage of milk. If the storage temperature is above 8-10 °C, then already in the first hours after the bactericidal phase, various mesophilic bacteria begin to develop in milk. This period is called the phase of mixed microflora. By the end of this phase, mainly lactic acid bacteria develop, in connection with which the acidity of milk increases. As lactic acid accumulates, the development of other bacteria, especially putrefactive ones, is suppressed, the phase of lactic acid bacteria sets in, and the milk is fermented.

In milk stored at a temperature below 8-10 ° C, most lactic acid bacteria almost do not multiply, which contributes to the development of cold-resistant (psychrotrophic) bacteria, mainly of the Pseudomonas genus, capable of causing the decomposition of proteins and fat; the milk acquires a bitter taste. Rancidity in raw milk is also caused by bacteria of the genus Alcaligenes and the spore bacterium Bacillus cereus. Many studies (E. J1. Moiseeva, C. Comae and others) indicate that the organoleptic indicators of milk quality change when 106-108 bacteria are contained in 1 cm 3 of it.

Physical and chemical changes in the composition of milk can be associated with the appearance of somatic cells (X. Hauke, V. Schanherr). By origin, udder cells and blood cells are distinguished. Udder cells (epithelial cells) are formed in the udder during natural aging and renewal and are an integral part of milk. In the milk of a healthy cow, they make up 60-70% of the total number of somatic cells. The rest is represented by blood cells - leukocytes. Inflammatory phenomena in the udder (mastitis caused by staphylococci) are associated with an increase in the content of somatic leukocyte cells. Therefore, an overall high level of somatic cells serves as an indicator that milk is obtained from sick cows.

Currently, the determination of the number of somatic cells in milk is recognized worldwide as an indicator of the sanitary state of milk. In this regard, the current requirements of SanPiN 2.3.2.1078-01 "set the upper limits of the permissible content of somatic cells in 1 cm3 - in milk of the highest grade no more than 5 - 105, in milk of the first and second grade - no more than 1 106.

To keep it fresh, milk at a dairy farm or collection point is cooled to a temperature of 5-3 "C and delivered to dairies in a chilled state. It is cleaned of mechanical impurities, pasteurized or sterilized, cooled, poured into flasks, tetra-packs or other containers and sent to implementation.

The main indicator of the quality of raw milk is its total bacterial contamination.

To improve the preservation of raw milk, in addition to cooling, it is recommended to introduce limited amounts of sodium thiocyanate, hydrogen peroxide, carbon dioxide into it.

Purpose of pasteurization milk is the destruction of pathogenic bacteria in it and perhaps a more complete reduction in the total contamination with saprophytic bacteria. The efficiency of milk pasteurization depends on the quantitative and qualitative composition of its microflora, mainly on the number of heat-resistant bacteria. The higher the contamination with them, the less effective the heat treatment. Drinking milk is usually pasteurized at 76°C for 15-20 seconds. The mode of pasteurization of milk used for the manufacture of fermented milk products is more stringent.

Pasteurization retains a certain amount of vegetative cells of thermophilic and heat-resistant bacteria, as well as bacterial spores. In the residual microflora of milk, lactic streptococci of fecal origin (enterococci) are found mainly, in small quantities - spore bacilli and micrococci.

The microflora of pasteurized milk coming out of a pasteurizer and milk produced by a factory can differ significantly. On the way from the pasteurizer to bottling into containers, milk can become infected with microorganisms (from milk pipelines, equipment), many of which are able to multiply at low positive temperatures. The degree of secondary contamination of pasteurized milk depends on the sanitary and hygienic conditions of production.

After pasteurization, milk is subjected to deep cooling - up to 6-4 ° C, otherwise it quickly turns sour.

Residual microflora of pasteurized milk can cause spoilage due to fermentation, breakdown of proteins, fats, etc. flasks and tanks - 2 105 in 1 cm3. Bacteria of the Escherichia coli group are not allowed in 0.01 cm3, Staphylococcus aureus - in 1 cm3 (for milk in consumer packaging), in flasks and tanks - in 0.1 cm3;

2. Microbiology of meat and sausages

Meat is a good nutrient substrate for many microorganisms; the content of available water and the pH of the meat also favors their development, in connection with which the meat quickly spoils.

The muscles of healthy animals are usually sterile. The muscles of sick animals that have undergone starvation before slaughter, severe overwork, or for other reasons that contribute to the weakening of natural resistance and the penetration of bacteria from the intestines, may contain microorganisms. In addition to intravital endogenous infection, muscles can be contaminated with microbes after the slaughter of the animal, from the outside (exogenous contamination) during the primary processing and cutting of carcasses (especially if the intestines are damaged) from the tools, hands and clothes of workers. Therefore, the microflora of freshly processed meat is diverse in number and composition. To prevent the development of microflora, the meat is quickly cooled. The contamination of freshly processed chilled meat with microorganisms can vary depending on the timeliness of the removal of the viscera, the degree of bleeding, the maturation of the meat, the temperature and humidity conditions of cooling, the sanitary and hygienic conditions of production, transportation, storage and sale. On 1 cm2 of the surface, there are from 10 3 to 10 6, and in some cases even more cells.

The composition of the microflora is diverse. These are mainly aerobic and facultative anaerobic spore-free gram-negative rod-shaped bacteria of the genera Pseudomonas, Flavobacterium, Alcaligenes, Aeromonas, bacteria of the Escherichia coli and Proteus groups, coryneform bacteria, lactic acid bacteria, and various micrococci. In smaller quantities, aerobic and anaerobic spore-forming bacteria, yeasts, and mold spores are found. Among these microorganisms, there are many possible pathogens of meat spoilage that can actively affect proteins, fat and other substances that make up its composition.

Meat can also be infected with toxigenic bacteria, such as Clostridium perfringens, Salmonella, Listeria, Bacillus cereus, Enterococci. Salmonella often cause intestinal diseases in cattle, after which the animals are bacillus carriers for a long time. The penetration of Salmonella into the muscles is possible during the life of the animal. If these bacteria multiply, meat can cause poisoning when used.

Meat offal (brains, kidneys, heart, etc.), due to the relatively high content of blood and moisture in them, is usually more contaminated with microbes than meat, and therefore undergoes faster spoilage.

Reproducing under favorable conditions on the surface of the meat, microorganisms gradually penetrate into its thickness.

The temperature is crucial for the rate of microbial reproduction, and hence the spoilage of meat kept refrigerated.

Many studies have established that signs of spoilage of a product appear when bacteria accumulate in it in an amount of 10 7 -10 8 per 1 g or 1 cm2 of its surface (depending on the type of bacteria and product). The time to reach this "threshold" concentration of microorganisms depends mainly on the storage temperature and the initial number of microorganisms on the product that can multiply at a given temperature. So, according to E. JI. Moiseeva, with an initial degree of seeding of meat 10 4 cells per 1 cm2 of surface, the approximate shelf life at a temperature of 0 to -1 ° C is 7-9 days, at 10 5 - 3-4 days, and at 10 8 - a day.

The spoilage of chilled meat can manifest itself in different ways - depending on the storage conditions.

At a temperature of 5 ° C and above, putrefactive processes develop, caused by aerobic and anaerobic mesophilic microorganisms that have active proteolytic properties. In the initial stages of the process, mainly coccal forms of bacteria are involved, then they are replaced by rod-shaped bacteria. Of the aerobes, the most active are bacteria of the genus Pseudomonas, Bacillus subtilis, Alcaligenes faecalis; from facultative anaerobic - proteus (Proteus vulgaris) - from anaerobes, Clostridium sporogenes, Cl.putrificum often develop. The spoilage of meat at the above temperature occurs very quickly - within a few days. Opportunistic and pathogenic microorganisms can also develop.

When meat is stored at temperatures below 5 °C, the composition of its initial microflora gradually changes and becomes more uniform. Mesophilic bacteria stop multiplying, and some even die off. Psychotrophic microorganisms develop; the first place (up to 80% or more of the entire microflora) is occupied by non-spore-forming bacteria of the genus Pseudomonas. Many of them have not only proteolytic, but also lipolytic activity. Pseudomonas are the main causative agents of spoilage of chilled meat stored at low positive temperatures under normal (aerobic) conditions. The predominance of Pseudomonas is not only the result of their increased cold resistance and reproduction rate compared to other microorganisms found on chilled meat, but also their ability to inhibit the development of many bacteria.

Cold-resistant species of the genera Flavobacterium, Micrococcus, Acinetobacter take part in spoilage, but to a much lesser extent.

With putrefactive spoilage, the color of the meat becomes gray, it loses its elasticity, becomes slimy, softens. At first, a sour, and then an unpleasant, putrid smell appears, which intensifies as the process deepens. There is a decomposition of proteins, amino acids with the formation of organic acids, amines, ammonia, hydrogen sulfide, phenols, indole and other substances. There is a hydrolytic breakdown of fat with subsequent transformations of fatty acids. Fat becomes dirty gray, smeared, with a mucous surface; carbohydrates are also broken down. In addition to changes in the chemical composition and organoleptic properties, microstructural changes in meat also occur under the influence of microorganisms: lysis of the nuclei of connective tissue cells and muscle fibers, destruction of connective tissue, disappearance of transverse and longitudinal striation of muscle fibers and violation of their integrity.

slime- the earliest common type of spoilage of cooled and chilled meat, especially if it is stored in conditions of high relative humidity (over 90%). This defect is caused mainly by bacteria of the genus Pseudomonas, often micrococci also cause mucus.

Mucus is expressed in the formation of a sticky layer of mucus of a dull gray color on the surface of the meat. The number of bacteria in it reaches tens, hundreds of millions and even billions per 1 cm3. It was established (V. V. Eremenko) that abundant mucus formation in these bacteria manifests itself at temperatures from 2 to 10 ° C; mucus accumulates (albeit more slowly) even at -2 °C.

acid fermentation(souring of meat) is accompanied by the appearance of an unpleasant sour smell, the formation of gray and greenish-gray color on cuts and softening of the meat. This process can be caused by anaerobic bacteria Clostridium putrifaciens, lactic acid, and sometimes yeast.

Acid fermentation of meat often occurs due to poor bleeding of animals during slaughter, as well as in cases where carcasses are not cooled for a long time.

meat pigmentation- the appearance of colored spots - is associated with the development of pigment microorganisms on its surface. Thus, the development of the “wonderful stick” (Serratia marcescens) or non-spore-bearing yeast of the genus Rhodotorula leads to the formation of red spots that are not characteristic of meat, while the development of non-pigmented yeast produces a white-gray coating.

mold due to the growth of various molds on the surface of the meat. Their development usually begins with the appearance of an easily washable cobweb or powdery white coating. In the future, more or less powerful raids are formed. On chilled meat, mucosal fungi can develop - Mysog, Rhizopus, Thamnidium, forming white or gray fluffy raids. Black plaque gives Cladosporium, green - fungi of the genus Penicillium, yellowish - Aspergillus. Thamnidium and Cladosporium are proteolytically and lipolytically active and, with significant growth, can cause profound changes in proteins and fat, especially since Cladosporium can grow into the thickness of the meat. Cleaning meat only improves its appearance, but does not eliminate the changes caused by mold, although in shallow layers of meat.

In addition, some molds found on meat are capable of producing toxic substances. Molding of chilled meat usually occurs at high humidity in the chamber.

Optimal storage conditions chilled meat is considered to be a temperature from 0 to -1 "C and a relative humidity of 85-90%, but even in such conditions the meat is stored for no more than 10-15 days. At nearly cryoscopic temperatures of -2, -3 ° C (slight freezing) the shelf life This temperature should be strictly maintained: when it rises, the surface of the meat is moistened, which favors the development of microbes, i.e., accelerates the spoilage of meat.

Meat semi-finished products, especially small pieces and minced meat, deteriorate faster. Usually they contain more microorganisms than the meat from which they are made, as they are infected during the manufacturing process from the outside (from equipment, inventory, from the air). In addition, due to the increase in surface and humidity, minced meat is a more favorable environment for the development of microbes.

To extend the shelf life of chilled meat, in addition to cold, it is possible to use additional means of influencing microorganisms: increasing the content of carbon dioxide in the atmosphere (up to 10-15%), ultraviolet irradiation, periodic ozonation (with an ozone content of up to 10 mg / m3) storage chambers.

Techniques for storing meat and meat products under anaerobic conditions are being developed: in vacuum packaging, packaging from a gas-tight film. The effectiveness of this method of storing beef cuts, natural meat semi-finished products has been shown by many researchers. However, although the shelf life increases, the meat is subject to spoilage due to the development of some facultative anaerobic psychrotrophic bacteria.

Minced meat packed in a film that is limitedly permeable to gas (PC2) and gas-tight (saran) is stored at a temperature of 2-1 ° C 3-4 times longer than minced meat wrapped in cellophane (K. A. Mudretsova-Viss and G. M. Gabrielyants). Minced meat stored under anaerobic conditions becomes sour, which is due to the action of predominantly rod-shaped lactic acid bacteria (Lactobacillus genus), as well as non-spore cold-resistant bacteria of the Aeromonas genus. Compared with Pseudomonas, the main causative agents of spoilage of chilled meat stored under normal aerobic conditions, lactic acid bacteria multiply much more slowly at 0 °C. The inhibition of the development of aerobic spoilage pathogens is explained not only by the restriction of oxygen access, but also by the accumulation of CO 2 under the packaging.

Storage, transportation and sale of packaged meat and meat products also play a positive role in sanitary and hygienic terms.

The shelf life of cooled meat in a nitrogen atmosphere increases significantly.

Promising (according to literature data, domestic and foreign) is the radurization of chilled meat - processing it with moderate doses of y-radiation exercises. Studies conducted at VNIKOP (T. S. Bushkanets, S. Yu. Gelfand, M. JT. Frumkin and others) showed that irradiation of raw meat semi-finished products with a dose of 2-3 kGy reduces the contamination of the product with bacteria by hundreds, thousands or more once. This significantly changes the composition of the microflora of meat. Radiosensitive bacteria of the genera Pseudomonas, Flavobacterium, Proteus die or remain in small quantities. In the residual microflora of irradiated chilled meat, micrococci and yeasts (Torulopsis and Candida) predominate, lactic acid and spore-forming bacteria are found in small quantities. These radioresistant microorganisms do not cause noticeable putrefaction of meat. They develop relatively slowly at positive low temperatures. Meat spoilage is manifested in the appearance of an extraneous slightly acidic odor and a slight change in color and taste.Most of the toxigenic bacteria found on raw meat have low radio resistance: a radiation dose of 2-4 kGy causes the death of many of them, and subsequent storage at 0-2 "C prevents the surviving from multiplying.

The domestic and foreign literature provides data on the prospects of using mixtures of organic acids (citric, sorbic, propionic, acetic, etc.) and their salts for surface treatment of chilled meat; bactericidal compositions from essential oils of various spices.

The effectiveness of the use of additional means of influencing the microflora of the product entering storage largely depends on the degree of its contamination with microorganisms. If the meat has been significantly contaminated with proliferating microorganisms, then even under storage conditions that retard their growth, the meat undergoes spoilage under the action of enzymes secreted by microbes.

3. Microbiology of eggs and egg products

Eggs are a good nutrient substrate for microorganisms. However, the contents of the egg (white and yolk) are protected from their penetration by the shell and shell membranes. An egg freshly laid by a healthy bird is usually free of germs.

The sterility of the egg can be preserved for some time, as it has immunity. A significant role in immunity is played by the proteins contained in the egg (lysozyme, ovidin, etc.), which have bactericidal properties.

During storage, the egg ages and the faster, the higher the storage temperature, so the eggs are quickly cooled after removal. With a decrease in immunity, conditions are created for the penetration and reproduction of microorganisms in it. Some microbes mechanically penetrate through the pores of the shell; others, especially molds, grow through the shell. Moisturizing it favors the germination of mold spores. Hyphae of the fungus, penetrating the shell and shell membrane of the egg, contribute to the penetration of bacteria.

The microflora of eggs can be of endogenous, or lifetime, origin (in birds with tuberculosis and salmonellosis, pathogens enter the egg during its formation in the ovary and oviduct) and exogenous (contamination of the shell from the outside after laying).

On 1 cm 2 of the surface of uncontaminated eggs there are tens and hundreds of bacteria, and on a contaminated shell - hundreds of thousands and even millions of cells.

The bacterial flora of the egg surface is diverse; it contains bacteria from the intestines of birds, air, soil, etc. These are mainly bacteria of the group of Escherichia coli, Proteus, spore bacteria (Bacillus subtilis, etc.), various types of Pseudomonas, micrococci, mold spores. Pathogenic microorganisms (salmonella, staphylococcus) can also occur. There are known cases of poisoning when eating eggs and products made from egg products.

Eggs with contaminated shells are not allowed for retail sales; they must be washed. For washing, use high-quality water with the addition of detergents and disinfectants permitted by the Ministry of Health of the Russian Federation. Washed eggs are unstable, therefore, to prevent rapid spoilage, it is advisable to treat them with film-forming substances.

Microorganisms that enter the egg usually develop near the point of penetration; their resulting accumulations (colonies) are visible during visual ovoscopy (transmission) in the form of spots. Further reproduction of microbes leads to various changes in the proteins and lipids of the egg, to its deterioration.

Bacteria multiply in the protein more slowly than in the yolk, since the protein contains antimicrobial substances, as well as a high pH value (more than 9.0).

The rate of spoilage of eggs depends on the storage temperature, relative humidity, shell condition, composition of microflora. The condition of the container and packaging material is of great importance. Eggs with dirty and damp shells spoil much faster than those with clean and dry ones.

Among bacteria, the most common spoilage agents are Pseudomonas fluorescens, Proteus vulgaris, Micrococcus roseus, Basillus subtilis, Clostridium putrificum, Cl.sporogenes.

Under conditions of refrigerated storage, bacteria of the genus Pseudomonas develop predominantly. These bacteria quickly penetrate from the surface of the shell into the egg; in a day they are found on the shell membrane, and after two - even in the contents of the egg.

Bacteria that cause spoilage differ in biochemical properties and activity, so the changes they cause are very diverse. Some bacteria affect protein. The breakdown of protein is accompanied by the accumulation of acids and bases, ammonia, hydrogen sulfide, carbon dioxide. There can be so much gas that the shell breaks. The protein acquires an unusual color (redness, yellowing, blackening) and an unpleasant odor (putrefactive, cheesy, musty). The yolk may not change. Other bacteria act on the yolk, causing hydrolytic and oxidative lipid conversion; in this case, fatty acids, aldehydes, ketones are formed.

Often, the protein is mixed with the yolk and a homogeneous, cloudy, brownish liquid mass with an unpleasant odor is formed. With ovoscopy, such an egg is not translucent.

The sour egg defect is caused by many bacteria, including E. coli. When determining the light transmission of such an egg, the defect is not detected, and when opened, the egg emits a pungent odor.

Molds grow primarily on the shell membrane and most rapidly near the air chamber. Then they penetrate the protein. In the initial stage of molding, when ovoscopy of the egg, a dark spot is observed at the site of mold development. As the fungus develops, the size of the spot increases and the egg becomes completely opaque, as the entire shell is covered with mold from the inside. Spoilage of eggs is most often caused by Penicillium, Cladosporium, Aspergillus, and yeast - Torulopsis vicola.

Salmonella, the causative agents of food poisoning, are often found in the eggs of waterfowl (duck, goose). For their development, the most favorable part of the egg is the yolk. In order to prevent food poisoning, the sale of duck and goose eggs in catering establishments and in trade is prohibited.

Eggs of hens with tuberculosis are used only for the production of confectionery products, which are subjected to heat treatment at high temperatures.

Chilled, fresh, clean eggs are laid for long-term storage. Store them at a temperature of -1 to -2 ° C and a relative humidity of 85-88%. With sharp fluctuations in temperature, the shell is moistened (“sweating”), which contributes to the development of microorganisms.

To protect against the penetration of microbes and prevent loss of moisture and carbon dioxide, and therefore, to extend the shelf life of the egg, instead of the previously used liming (to clog pores), its surface is covered with thin films. A good effect is obtained by treatment with mineral oil by short-term immersion in it. So, for 5 months of storage at -2 ° C, the food rejection of eggs treated with oil amounted to 0.3% of the total, treated with vaseline - 0.5, and untreated - 2.5%. The effect also increases when the antibiotic herdecin is added to the oil (R. A. Didenko). Eggs are treated with water-soluble film-forming substances (polyvinyl alcohol, methylcellulose, etc.), after which they are dried in air. According to V. A. Gerasimov, for 5 months of storage of eggs at a temperature of 1 to 1.5 ° C, the number of bacteria on the shell with a film coating decreases from 10 4 per 1 cm 2 of the surface to tens of cells, and on an untreated shell - only to 10 3 . There are no bacteria in the protein of processed eggs, and in untreated eggs they are found in the amount of hundreds per 1 cm 3; decreases several times and the number of food defects. However, these film coatings can themselves be destroyed by microbes.

VNIITOP has developed a method for creating a moisture- and gas-protective bactericidal film of paraffin and petrolatum on the shell, followed by ozone treatment. With their rapid oxidation, substances are formed that have a bactericidal effect (higher fatty acids, fatty alcohols, etc.). On the shell of eggs treated in this way for 6 months. storage in refrigerators, bacteria were not detected. It is recommended, in addition to cold storage of eggs in a modified gas environment - with a high content of carbon dioxide and nitrogen; treatment with a high-frequency electromagnetic field, which allows (by modulating the amplitude) simultaneously, but selectively, to heat the shell and the contents of the egg to different temperatures; ozonation. Ozonation of eggs during long-term storage allows to reduce waste by 2-3 times. Efficiency is increased by combining the ozonation of eggs with their subsequent packaging in a sealed polymer container. The container and packaging material must be clean and dry.

In the production of bread, the quality of flour and the composition of its microflora are of great importance for the normal course of the dough making process and are reflected in the quality of the semi-finished product - dough and finished bread.

At bakeries, flour is examined - the degree of its contamination with spores of Bacillus subtilis, the causative agent of a lingering disease of bread, is determined directly by the microbiological method or by the method of trial bread baking.

Along with the physical and biochemical transformations occurring in it (both from wheat and rye flour), yeast and lactic acid bacteria play an important role in maturation of the dough.

In the production of wheat bread, in the manufacture of dough, baker's pressed or dry yeast is used, as well as liquid yeast and liquid wheat sourdough, produced directly at bakeries.

Baker's yeast must be resistant to elevated concentrations of the medium and have high fermentation maltase activity, since maltose accumulates mainly in the dough as a result of the enzymatic breakdown of starch. The carbon dioxide formed during the fermentation process loosens the dough and it increases in volume; the resulting alcohol is removed during the baking process.

Some yeast waste products (higher alcohols, aldehydes, ketones, etc.) give bread a peculiar taste and aroma.

Liquid yeast is an active yeast culture grown on a flour nutrient medium, previously saccharified and fermented (to a certain acidity) with a thermophilic lactic bacterium - Delbruck's bacillus. The high acidity of the medium favors the development of yeast and inhibits the growth of extraneous microflora present in the dough, which inhibits the vital activity of yeast.

In the manufacture of liquid yeast, pure cultures of various industrial races of the Saccharomyces cerevisiae species are used.

The sourdough always contains a certain amount of lactic acid bacteria, mostly heterofermentative ones.

Liquid wheat sourdough is a mixed culture on a saccharified flour medium of active yeast S.cerevisiae and mesophilic lactic acid bacteria: homofermentative bacterium Lactobacillus plantarum and heterofermentative L.brevis, developing spontaneously in the medium or introduced as pure cultures. Heterofermentative lactic acid bacteria, in addition to acids, form carbon dioxide, so they play a role in leavening the dough. Lactic acid and volatile acids secreted by lactic acid bacteria improve the aroma and taste of bread.

Bread made with liquid yeast and liquid sourdough not only has a more pleasant taste, but is less likely to suffer from a lingering disease and stale more slowly, compared to bread made using only pressed yeast. There are few lactic acid bacteria in wheat dough based on pressed yeast, they mainly come from flour, their participation in dough maturation is insignificant.

In the production of rye bread, the dough is prepared on sourdoughs, which, like wheat sourdoughs, are mixed cultures of yeast and lactic acid bacteria, which provides loosening of the dough and the accumulation of acids. The ratio of lactic acid bacteria and yeast is 80: 1, and in wheat dough - 30: 1, i.e. in the maturation of rye dough, the leading role belongs to lactic acid bacteria.

Rye sourdoughs are thick and liquid. Liquid ones are prepared on a saccharified liquid medium from rye flour using pure cultures of various strains of yeast species Saccharomyces cerevisiae and S. minor. From homofermentative lactic acid bacteria, Lactobacillus plantarum is used (sometimes L. casei is introduced), from heterofermentative - L. brevis and L. fermentum.

At most factories, thick starters are prepared on pure cultures of yeast - S. minor and lactic acid bacteria - L. plantarum and L. brevis. These bacteria, in addition to lactic acid and carbon dioxide, produce substances (aldehydes, volatile acids, acetic and ethyl esters) that are part of the aromatic complex of bread.

The yeast S. minor is somewhat inferior in fermentation energy to the species S. cerevisiae, but is more acid-resistant.

The high acidity of rye dough (pH 4.2-4.3) has a beneficial effect on the proteins of rye flour, improves its baking properties and prevents the development of spoilage bacteria in dough and bread.

In the test, in addition to the industrial microorganisms used, there are always foreigners that enter with the raw materials and from the external environment. Their active development disrupts the normal course of fermentation and dough maturation processes. These are, for example, wild yeasts of the genus Candida that come with pressed yeast and from flour. These yeasts do not participate in fermentation, but they negatively affect the fermentation activity of industrial yeast. In addition, they oxidize alcohol to acetic acid, use lactic acid, thereby reducing the acidity of the starter.

The surface of the bread is practically sterile when leaving the oven, but the crumb is heated only to 93-98 °C, and a certain amount of bacterial spores is always stored in it; vegetative cells can also be preserved.

During cooling, subsequent transportation, storage and sale of bread, spores can germinate, and the reproduction of cells in the crumb leads to spoilage of the bread.

During storage, bread can be subject to various types of spoilage.

The causative agent of viscous potato disease is the spore-forming aerobic bacteria potato and hay sticks, currently combined into one species - Bacillus subtilis. The spores of these bacteria are heat-resistant, they are always present in flour, and in certain types (2nd grade flour, wallpaper) - in considerable quantities. The source of infection is the equipment, the air of the production shops of the bakery. During the baking of bread, the spores of these bacteria do not die and later, under favorable conditions, germinate into vegetative, multiplying cells.

Bacillus subtilis causes the hydrolysis of starch with the formation of a large amount of dextrins, but these bacteria are sensitive to high acidity of the environment, therefore wheat bread, especially from flour of the 2nd grade, which has a low acidity compared to rye bread, is susceptible to a viscous disease. At the beginning of the development of the disease, the bread acquires an extraneous fruity smell, then the crumb becomes slimy, darkens, becomes sticky, stretches with threads. Affected bread is unsuitable for food.

If signs of potato disease are found during storage or sale, bread and bakery products must be immediately removed from the utility rooms and the trading floor and sent to livestock feed or destruction in the prescribed manner.

In order to prevent a lingering disease, bread after baking is quickly cooled to a temperature of 10-12 ° C and stored at this temperature in a well-ventilated room. It is recommended to acidify the dough with acetic, propionic and sorbic acids or their salts.

It was proposed (K. E. Berteneva) to introduce starter cultures of pure cultures of propionic acid bacteria or mesophilic lactic acid bacillus - Lactobacillus fermentum into the dough from wheat flour. The inhibitory effect of this bacterium on Bacillus subtilis is due not only to acidification of the environment, but also to the release of anabiotic substances.

Drunk bread does not have external signs of spoilage, but is harmful, as it contains mycotoxins of the Fusarium fungus, preserved during baking, released into the grain.

The causative agents of the Cretaceous disease are yeast-like fungi (from endomycetes). They get into the dough with flour and are preserved when baking bread; infection of the finished bread can also occur from the outside. The disease first manifests itself on the surface of the bread, then spreads through the cracks inside the crumb in the form of white dry powdery inclusions similar to chalk. Bread loses its presentation, acquires an unpleasant taste and smell.

Molding is the most common type of spoilage in rye and wheat bread; occurs mainly when the storage mode is violated. With too dense packing, high humidity and temperature, mold spores that have fallen on wheat bread from the outside (from the air, through contact with infected objects) develop quickly, especially if the bread crust is cracked. Molding of bread is more often caused by fungi of the genera Penicillium, Aspergillus, Mucor, Rhizopus. Many of them cause hydrolysis of proteins, starch; bread acquires an unpleasant musty smell and taste. Moldy bread is unsuitable for food, as it may contain mycotoxins. In bread affected by Aspergillus fungi, aflatoxins (Spicher) were found, which were concentrated mainly in the outer layers of bread, but were also detected in the crumb.

To combat molding of bread, various methods are proposed: treatment of the surface of bread or packaging material with chemical preservatives (ethyl alcohol, salts of propionic and sorbic acids), sterilization of packaged bread with high-frequency currents, ionizing radiation; Freezing bread is also effective. However, the main measures at bakeries that ensure the high quality of bread are strict adherence to the established technological regime, keeping equipment in proper cleanliness, and systematic disinfection of production facilities.

Bread is eaten without additional culinary processing, therefore, at all stages of its production, during storage, transportation and sale, the established sanitary requirements must be strictly observed.

Topic: "Biodamage of non-food products"

The impact of living organisms on industrial raw materials, materials and products can significantly change their consumer properties, reduce quality, and in some cases lead to their complete destruction.

The properties of raw materials, materials and products, including consumer ones, can change during storage, operation, and sometimes during production under the influence of physicochemical, mechanical and biological factors that cause corresponding damage (physicochemical, mechanical, biological).

These damages occur in parallel or sequentially, reinforcing each other.

There is no doubt that in case of any violations of storage regimes, especially in emergency situations (for example, soaking), in the end, biological damage is the predominant and final process.

According to regulatory documents, the concept of biodamage is defined as damage to materials, raw materials and products under the influence of a biological factor (GOST 9.102-91 ESZKS. The impact of biological factors on technical objects. Terms and definitions).

Biological factor (biofactor) - these are organisms or communities of organisms that cause a violation of the working state of an object.

However, the wordings presented in the standard do not reflect another aspect of the impact of industrial products biodamage on one of the most important consumer properties - safety.

Safety is the absence of risk to the life, health and property of consumers during the operation or consumption of goods.

Allocate sanitary and hygienic safety, which means the absence of an unacceptable risk that may arise from various kinds of biodamage to consumer goods and which, in turn, can not only lead to loss of property, but can also be hazardous to the health of consumers.

This is especially true, for example, of cosmetic products or contamination of products with pathogens.

However, it is not only pathogens that can be hazardous to the health of consumers. For example, at some textile enterprises, cases of illness in workers' spinning and preparatory sections have been identified due to the release into the air of a large number of dust particles with saprophytic microorganisms from biocontaminated cotton.

When hygienic assessment of clothes, underwear, shoes, etc. they determine the degree of accumulation of microorganisms. It is believed that the greater the accumulation of microorganisms on underwear and in the interior of shoes (gloves, hosiery, insoles), the less they remain on the surface of the skin, since these products have a high cleaning ability. It was revealed that the contamination of the skin when using clothes and linen made of cotton and viscose is 2-3 times less than when using linen made of nylon.

Thus, biodamage is closely related to such complex indicators of product quality as reliability, functionality, ergonomics, etc.

Objects of biodamage are structures, products, materials, raw materials, which, in the process of exposure to them by living organisms, lose their properties.

Agents of biodamage are living organisms that attack structures, products, materials and raw materials and cause changes in their properties.

Under real conditions of storage and operation, non-food raw materials, materials and products are damaged by microorganisms (bacteria, microscopic fungi), insects (moths, leather beetles, grinder beetles, termites, cockroaches) and mammals (rodents: rats and mice).

Resistance to biological factors (biostability ) is the property of an object to maintain the value of indicators within the limits established by regulatory and technical documentation for a specified time during or after exposure to a biofactor. This term is used with a specific biofactor:

bacterioresistance - resistance to bacteria;

mushroom resistance - resistance to the effects of fungi;

resistance to termite damage;

resistance to moth damage;

resistance to damage by rodents;

microbiological resistance - the stability of materials during tests for biostability in natural conditions.

The impact of living organisms on materials can lead to an unfavorable or favorable outcome for humans. In the first case, we are talking about biodeterioration (English - biodeterioration), in the second - about biodestruction (English - biodegradation) of materials that have served their time and pollute the environment.

Among biodamages, it is worth noting the actual biodamages of materials, which, with all the variety of living organisms and methods of their action, are reduced to chemical and mechanical changes.

Microorganisms in this case primarily have a chemical effect on materials, while insects and animals usually cause mechanical damage.

2. Thus, the actual damage to materials by living organisms can be reduced to two types:

1) the use of the material as a source of nutrition (in the case of microorganisms, we are talking about assimilation; in the case of insects and rodents, we talk about "food" damage);

2) impact on the material, which is not associated with the nutrition process and leads to mechanical or chemical destruction of the material (in the case of microorganisms, this is destruction; in the case of insects and rodents, these are "non-food" damage).

It should be noted that, of all microorganisms, microscopic fungi can also contribute to the mechanical destruction of materials, which occurs due to the growth of hyphae of the mycelium of the fungus, which develop high turgor pressure.

One of the types of harmful effects of living organisms (mainly microorganisms and plants) on raw materials, materials and products is surface fouling. It may be accompanied by a chemical attack on the material or occur without it.

The third type of impact of the biological factor is biofouling.

Biological contamination of an object (biocontamination) is the state of an object associated with the presence of a biofactor, after the removal of which the functional properties of the object are restored.

Thus, microorganisms developing on materials and substrates can be of several types. Some use the organic matter of the materials themselves as a source of nutrition and energy (assimilation). Others develop through the use of metabolites of the former, but they can also cause damage to materials by their metabolic products (destruction). And, finally, third microorganisms develop on the surface of materials only due to dust, mineral and organic contaminants, without affecting the material itself, and only cause its biocontamination.

Damage caused by insects to raw materials, materials and products may be food or non-food in nature.

In most cases, food damage is caused by larvae that live inside or on the surface of the material. If the products have cavities and holes convenient for the settlement of insects, then only internal contamination of the product is possible. If insects that develop in the cavities of the material use its particles for construction activities, as, for example, some moth caterpillars when building a cap, then the material itself is already damaged to some extent. The most characteristic of insect pests is the use of materials of plant and animal origin for food, and pests of plant materials are more diverse. Synthetic materials are damaged by insects through accidental contact.

Among living organisms that damage materials, rodents occupy a special position, since the damage they cause is most often of a non-food nature and is associated with the manifestation of gnawing activity.

As a result of the impact of living organisms on raw materials, materials and products, defects occur in them.

3. By degrees of significance Distinguish between critical, major and minor defects.

critical defects - non-compliance of products with established requirements that may harm the health or property of consumers or the environment.

Significant defects - affect the properties of materials, but do not affect safety for the consumer or the environment.

Minor defects - do not affect the properties of products, primarily, the purpose, reliability and safety. These include, in particular, biocontamination.

Depending on the availability of methods and means detection defects are divided into obvious, for which methods and means of detection are provided, and hidden, for which it is possible to use special methods and means of detection.

For biodefects, it is precisely hidden defects that are characteristic, for the detection of which special equipment is needed.

Depending on the availability of methods and means of elimination, defects are divided into removable and unrecoverable.

Removable - defects, after the elimination of which the product can be used for its intended purpose. Such defects are typical only for biofouling.

Fatal - defects that are impossible or economically unprofitable to eliminate. For example, if the optics are biodamaged, the device can be restored only after disassembly and additional surface polishing. In other cases, critical defects in biodamages are practically unremovable.

Thus, with biodamage of raw materials, materials and products, the following occurs:

change in chemical properties as a result of oxidation or hydrolysis of material components: under the influence of microorganisms, acid and alkali resistance, resistance to oxidizing agents, reducing agents and organic solvents change;

changes in the physical and mechanical properties of materials, for example, loss of strength of wood, rubber, plastics, fabrics under the action of microorganisms or their metabolic products, swelling of rubber, loss of adhesion of paint and varnish coatings;

change in optical properties, for example, color, gloss, transparency, refraction of light;

deterioration of electrophysical properties, for example, a decrease in the electrical insulating properties of materials;

change in organoleptic properties, for example, the appearance of a bad smell when rotting, the appearance of mucus on hard surfaces;

loss of part of the material due to its damage, for example, by rodents or insects.

1. Agents of microbiological impact on materials are:

2) insects

3) microscopic fungi

4) rodents

5) plants

2. Which of the enzymes play the greatest role in the biodegradation of materials of protein origin:

1) glycosidases

2) proteinases

4) isomerases

5) transferase

3. The degree of damage to woolen fabrics by moths according to GOST 9.055-75 is estimated:

1) in points

2) by biomass growth

3) by loss of mechanical strength

4) by color change

5) by smell change

4. Insecticides are used to protect materials from exposure to:

1) rodents

2) microscopic fungi

3) insects

4) bacteria

5) plants

5. The biological method of rodent control is to use:

2) traps

3) microorganisms

4) ultrasonic pesticide

5) insecticide

6. The most harmless to humans insecticides used to control cockroaches are:

1) organophosphorus compounds

2) carbamates

3) pyrethroids

4) biological preparations

5) karbofos

7. Biofactor used to assess the biostability of textile materials according to GOST 9.060-75:

1) standard set of bacteria

2) a standard set of microscopic fungi

3) enzyme preparation (cellulase)

4) soil microflora

5) a set of bacteria and microscopic fungi

8. The criterion for assessing the biostability of paper according to GOST 9.801 - 82 is:

1) breaking strength

3) weight loss

4) organoleptic indicators tensile strength

5) tensile strength

9. Microscopic fungi begin to develop on cotton fibers when they are wet:

1) not less than 20%

2) not less than 10%

3) not less than 45%

4) not less than 65%

5) not less than 85%

10. The following bast fibers are the most resistant to microorganisms:

1) jute

2) acetate

3) viscose

4) linen

5) polyester

11. Microbiological damage to wool fibers begins with the destruction of:

1) cuticles

2) cell-membrane complex

3) core layer

4) cortex

5) scaly layer

12. Defects in leather raw materials, the cause of which is the development of putrefactive processes:

1) fragrant

2) facelessness

3) whip

4) unseparated bakhtarma

5) stratification of the skin

13. Wood species with the lowest biostability:

14. Microorganisms develop in cosmetic emulsions:

1) in the aqueous phase

2) in the fat phase

3) on the surface of pigments

4) inside fat particles

5) outside fat particles

15. Which packaging of cosmetics can contribute to microorganism contamination when used:

1) aerosol cans

2) jars with a wide mouth

4) vials with dosing device

5) jars with a narrow neck

16. Bacteria that do not take part in the biocorrosion of metals:

1) sulfate-reducing

2) cellulose-destroying

3) thionic

4) iron bacteria

5) protelytic

17. On which substrate the biostability of paint coatings will be the least:

1) black metal

3) wood

4) non-ferrous metal

5) plastic

18. What plastic filler will increase fungus resistance:

2) cotton fibers

3) wood flour

5) linen fibers

19. Mark the correct statement regarding the microbiological stability of polymers:

1) the higher the amorphism, the higher the biostability

2) the higher the molecular weight and the higher the crystallinity, the higher the biostability

3) the lower the molecular weight, the higher the biostability

4) the lower the molecular weight and the higher the amorphism, the higher the biostability

5) the lower the amorphism, the higher the biostability

Topic: "Pathogenic microorganisms and foodborne diseases caused by them"

1. Nutritional (alimentary) diseases- diseases caused by food contaminated with toxigenic microorganisms or microbial toxins (Fig. 12.1).

Rice. 12.1 Foodborne diseases

Table 12.1 - Comparative characteristics of foodborne diseases

Food products are a favorable environment for the development of microorganisms - saprophytes, including pathogens of food poisoning. In addition, pathogens can also be transmitted through food products - contagious diseases that do not multiply directly in food products. Thus, food products with the wrong technological regime of their production and storage can cause foodborne diseases - food infections and food poisoning.

a) products of lactic fermentation;

b) products of mixed fermentation.

1. Oil microbiology. Oil defects.
2. Microbiology of cheeses. Cheese defects of microbial origin.

Dairy products contain easily digestible nutrients necessary for the body. Some of the dairy products have not only dietary, but also medicinal properties. According to the composition of microorganisms and the processes they cause, the products of lactic acid and mixed fermentation are distinguished.

Dairy products. Products of lactic fermentation. curdled milk is a widely used fermented milk product. Depending on the mode of heat treatment of milk and the composition of the microflora of the sourdough, different types of sour milk are distinguished: ordinary, Mechnikov (Bulgarian), southern, fermented baked milk, varenets, acidophilic and others.

Ordinary curdled milk prepared from pasteurized milk by adding 5% starter containing pure cultures of mesophilic lactic streptococci (Str. lactis and Str. cremoris). Milk is pasteurized at 85°C for 10-15 minutes. To give the finished product a certain consistency, sometimes 0.5% starter is added, consisting of a pure culture of Bulgarian sticks. At a temperature of 30°C, milk coagulates in 5-6 hours. The product acquires a dense texture and slightly acidic taste (acidity 90-110°T).

Mechnikovskaya (Bulgarian) curdled milk- fermented milk product, which is prepared from milk, pasteurized at a temperature of 85-90°C. The sourdough contains thermophilic lactic streptococcus and Bulgarian bacillus (Str. thermophilus and Lactobact. bulgari-cum). Milk is fermented at 40°C. After 3-4 hours, the milk coagulates, the acidity of the product reaches 70°T. Yogurt has a dense clot, creamy texture and sour taste. The higher the fermentation temperature, the greater the acidity of the product.

Southern curd. In pasteurized and cooled to 30 ° C milk, a starter is added, consisting of Bulgarian bacillus, thermophilic lactic streptococcus and lactose-fermenting lactose yeast culture. Fermentation of milk is carried out at a temperature of 45-50°C. The acidity of the product rises to 130-140°T, after which the curdled milk is cooled to 8-10°C.

Ryazhenka. For its preparation, milk containing up to 6% fat (a mixture of milk and cream) is used. Sterilization is carried out at 95°C for 2-3 hours. As a result, the product acquires a specific color, smell and taste. Milk is fermented with thermophilic races of lactic acid streptococcus. The resulting clot has a creamy color, dense texture and taste of pasteurized milk.

Varenets. Milk for Varents is sterilized in a steam sterilizer at 120°C for 15 minutes or boiled, cooled to 40°C and fermented with lactic streptococcus and Bulgarian bacillus. The finished product has a creamy color and taste of baked milk. Its acidity reaches 80-110°T.

Sour-milk drink "Snowball". It is made from pasteurized milk with 7% sugar content. The sourdough contains 4% thermophilic streptococcus and 1% Bulgarian bacillus. Fermentation is carried out at a temperature of 42-50°C. After 3 hours, the milk coagulates, the acidity reaches 80°T. After cooling the clot to 8-10°C, fruit syrup is added to it, stirred and bottled.

Acidophilic yogurt. It is prepared in the same way as Mechnikov's curdled milk, but acidophilus bacillus (Lactobact. acidophilum) is introduced into the sourdough instead of Bulgarian. Acidophilus bacillus, unlike Bulgarian, takes root in the gastrointestinal tract, that is, in the environment from which it is isolated, and therefore the effectiveness of such a fermented milk product is higher, and its effect is longer. Acidophilic yogurt is used for disorders of the gastrointestinal tract.

Products of mixed fermentation:

Kefir- fermented milk product, for the preparation of which fungi are used, which include mesophilic lactic acid microorganisms and yeast. Such symbiosis is the result of long-term cultivation of microorganisms in one medium. Outwardly, kefir fungi are light yellow protein formations of irregular shape (Fig. 53). They can be dry or wet. In the first case, they have a dense texture, in the second - loose. Dry fungi are inactive. Therefore, before use, they are placed for 12-24 hours in boiled and cooled to 30 ° C water, and then in warm pasteurized milk. During this time, the fungi swell and, after washing, can be used as a starter for making kefir.

Pasteurized milk is fermented with kefir fungi at a temperature of 20°C, and then at 10°C. Since the composition of the starter includes microorganisms with different optimal growth temperatures, by adjusting it, it is possible to change the course of the processes they cause. Cultivation of kefir at a temperature below promotes the development of yeast and an increase in the fermentation product - ethyl alcohol; at a higher temperature, lactic acid microorganisms develop more intensively, which increases the content of lactic acid in the product.

Depending on the ripening time of the product, weak kefir (one-day), medium (two-day) and strong (three-day) are distinguished. With an increase in exposure, the amount of ethyl alcohol (0.2; 0.4; 0.6%) and acidity (90; 105; 120) increase accordingly. Kefir can be fatty if whole milk is used, and skimmed, which contains many proteins and almost no fat.

Caucasian kefir made from milk, which is added with sugar and starter, consisting of lactic acid bacteria and yeast.

In such a product, a large amount of ethyl alcohol and carbon dioxide is formed, which gives it a sharp specific taste.

Kumys- dietary easily digestible fermented milk drink. It is prepared from the milk of mares or cows. Kumis, like kefir, is a product of mixed fermentation - lactic acid and alcohol, and alcohol fermentation plays the main role in such a product. The sourdough for koumiss is often the local curdled milk - katyk, which includes yeast, Bulgarian bacillus and thermophilic streptococcus. The finished product contains only yeast and lactic acid sticks. Streptococci are absent. This is due to the fact that after adding the starter, a rapid decrease in pH (4.0-4.2) occurs. In such an environment, the growth and development of streptococci cease.

Mare's milk has a lower buffering capacity than cow's milk. So, with the acidity of mare's milk 110°T, the pH value is 3.47; with the acidity of cow's milk 240°T - 3.52. That is why lactic acid sticks and yeast are found in the finished koumiss. Sticks are facultative anaerobes, yeasts are aerobes. Therefore, more intensive development of yeast is facilitated by frequent mixing, the entry of atmospheric oxygen into the environment. Yeast, fermenting milk sugar, form substances that retard the growth of tubercle bacilli. In this regard, koumiss is used in the treatment of people with tuberculosis.

Koumiss in most cases is prepared in a handicraft way - in linden or oak barrels. At a temperature of 25°C, 20-25% of the starter is added to fresh mare's milk and mixed with a whorl, as a result of which the acidity of the product increases, reaching 60-70°T. Koumiss is poured into bottles or other utensils, closed and after a short exposure (1-2 hours) left in the cold.

Koumiss is made from cow's milk after it has been skimmed and sugar has been added. Fermentation of such milk is carried out with pure cultures of Bulgarian and acidophilic lactobacilli and lactose-fermenting yeast.

Chal (shubat)- fermented milk drink obtained from camel milk. To prepare chal, unpasteurized milk is used, 10-40% of the finished product is added to it, which serves as a starter. The sourdough contains lactic acid bacilli (streptobacteria), lactic acid streptococci and lactose fermenting yeast. Fermentation of milk occurs at a temperature of 25-30°C for 3-4 hours, and after 8 hours the product is ready for use. Chal is a dietary product and is used for medicinal purposes. It is used for gastrointestinal diseases, tuberculosis, scurvy.

Chal can also be prepared from pasteurized milk using pure cultures that are part of the starter culture.

Oil microbiology. The oil contains valuable and easily digestible substances, so it can serve as a good environment for the development of microorganisms. Microbes get into the oil from raw materials, equipment, and the environment. The raw material for producing butter is cream, which must be fresh, clean, without foreign odors and tastes. The cream is subjected to pasteurization, as a result of which some enzymes (lipase, peroxidase, protease) are destroyed and up to 99.9% of microorganisms die. Pasteurization can be long-term and short-term. Long-term pasteurization is carried out in large containers while stirring the product for 30 minutes and heating it to 70°C. Short-term pasteurization takes place with the continuous movement of cream and heating them to 85-87°C.

Pasteurized cream is chilled. At a temperature of 1-8°C, the development of microorganisms stops and physical maturation of the cream takes place: fat compaction, viscosity increase, formation of oil lumps. The lower the temperature (plus), the worse the conditions for the development of microbes and the better for the maturation of the cream.

Microbes can get into the oil from the equipment. Its purity depends on the quality of washing, disinfection and rinsing water. Lactic acid, spore and other microbes are found on the walls of the apparatus. There are more of them in wooden butter makers and fewer in metal ones, since the latter can be more effectively sterilized. Water and its composition have a great influence on the quality of the oil. It can be the cause of many blemishes and sources of germs. Microbes also get into the oil from salt, therefore, before use, it must be treated with heat at a temperature of 150-180 ° C.

Sour cream butter contains tens and hundreds of millions of microbes, their increase is due to lactic acids, which are added to ferment the cream. Usually, there are more microbes during long-term (12-16 hours) fermentation of cream and less during short-term (20-30 minutes). After 4-6 weeks, the number of microbes decreases, by this time there are several tens of thousands of microbial cells in 1 g of oil. Sweet cream butter contains microbes that remain after the cream is sterilized, and also enter during its ripening and churning. The number of microbes in the product is affected by temperature: the higher it is, the more microbes. So, if 1 g of fresh sweet cream butter contains hundreds and thousands of microbial cells, then after a week at a temperature of 14-15 ° C, their number reaches hundreds of millions. At this temperature, mainly lactic streptococci develop. There are more unwanted microbes in sweet cream butter than in sour cream butter.

Microbiological processes during storage of oil and its defects. When oil is stored in it, along with chemical processes, microbiological processes also take place. Microbes are most often on the surface of the oil, among them putrefactive aerobes and mold fungi. These microorganisms break down proteins into fats. The resulting products give the oil an unpleasant odor and taste. Microbes cause the following oil defects.

Bitter taste. It appears as a result of the degradation of proteins by proteolytic bacilli and some fluorescent bacteria. Such a defect at a low positive temperature is observed in sweet cream butter.

rancid taste caused by mold fungi, some types of yeast, fluorescent, butyric and other microbes. They decompose fats into glycerol and fatty acids, and butyric acids also form butyric acid.

Spore-forming microbes can get into sweet cream and sour cream oils and cause fat decomposition in them. Therefore, it is necessary to comply with the pasteurization regime and protect products from foreign microflora entering them.

Sour taste observed in sweet cream butter at temperatures above 10°C, it is imparted to the butter by lactic acid, which is formed as a result of the fermentation of lactose by lactic acid bacteria. In sour cream butter, increased acidity is due to non-observance of the cream fermentation technology.

mold- the result of improper storage of oil (high humidity, high temperature, aeration of the oil surface). Molds are aerobic and are more common on wet, poorly protected oil surfaces. Among them, you can find Endo-myces lactis, Penicillium glaucum, Aspergillus, Mucor and other fungi. Mold inside the oil is rare and occurs if there are voids containing air in it. The denser the oil, the worse the conditions for the development of fungi. Observing the oil production technology, you can get a high-quality product without defects.

Microbiology of cheeses. For the correct course of microbiological processes, on which the quality of cheese depends, certain conditions and composition of raw materials are necessary. Not all milk can be used in cheese making. If it coagulates slowly or does not coagulate at all, then it is called cheese-unsuitable. There are many reasons for the cheese unsuitability of milk, however, this issue has not been fully studied.

Microbiological essence of cheese making. The process of cheese production includes the following operations: the formation of a casein clot and its processing, pressing and giving the cheese mass a certain shape, salting and maturation of the product. Pasteurized and raw milk is used to make cheese. Fresh milk is unsuitable. During pasteurization, micro-organisms are destroyed, which can cause swelling of cheeses and other defects. However, heating the milk slows down the clotting process, as calcium salts precipitate out.

Coagulation of milk (a method of obtaining protein in cheese-making) is carried out with the help of lactic acid microbes (in the production of sour-milk cheeses) and microbes in combination with rennet (in the production of other types of cheese). Under the action of microbes in the cheese mass, complex biochemical processes occur: maturation, the formation of organoleptic and other properties characteristic of a certain type of cheese. Cheese can be made from pasteurized milk by introducing pure cultures of lactic acid bacteria (sourdough). At the same time, their ability to form lactic acid, aromatic substances, and also destroy proteins is taken into account. The microorganism strain gives the product certain properties, so each type of cheese must have its own starter culture. Multi-strain starter cultures of the same type of bacteria adapt better to the changing conditions of the dairy environment.

In the production of hard rennet cheeses, bacterial starter is added in the amount of 0.2-0.5%, in the manufacture of soft cheeses - 3-5%. The composition of bacterial starter cultures includes acid-forming agents (Str. lactis and Str. cremoris), as well as microbes that form acid and aromatic substances (Str. diacetilactis, Str. paracitrovorum).

Depending on the mode of technology, Lactobact is also used. helviticum, Str. thermophilus and others, from antagonists of butyric bacilli - Lactobact. plantarum, etc.

Rennet is obtained from the abomasum of 2-3 week old calves. It is a powder that is added to milk to obtain a clot (gel). The activity of rennet should be 1: 100,000, that is, at a temperature of 35 ° C for 40 minutes, 1 g of the enzyme should coagulate 100,000 g (100 kg) of milk. In industry, a higher enzyme concentration of 2.5: 100,000 is used, that is, 2.5 g per 100 kg of milk. The optimum temperature for the action of the enzyme is 40-41°C, pH 6.2. Acceleration of the enzyme action occurs when 15-20 g of calcium chloride is added to 100 kg of milk. The composition of starter cultures varies depending on the type of cheese.

Rennet and lactic acid microbes cause the decomposition of proteins, and when combined, they have the greatest proteolytic activity than when separated. According to V. M. Bogdanov, under the action of rennet on milk proteins, the content of soluble nitrogen from the total amounted to 11.8%, under the action of Str. lactis -2.5%. With the simultaneous use of the enzyme and lactic acid streptococcus, the amount of soluble nitrogen in milk reached 60.5%. Rennet decomposes proteins to peptones, enzymes of lactic acid microbes to amino acids and ammonia. A deeper breakdown of proteins occurs in hard cheeses. The process of maturation of hard and semi-hard cheeses goes from the depth to the surface, soft - vice versa. Milk sugar is completely fermented during the ripening of cheeses.

Microbiological processes in the production of cheeses. In the cheese bath, the clot is cut, as a result of which it is dehydrated, releasing 90% of the whey, which creates conditions for the development of lactic acid microbes. The release of whey from the clot is facilitated by an increase in the free surface, waste products of lactic acid microbes, temperature and other factors. The bulk of microbes (up to 75%) remains in the clot, the rest is in the serum. In the process of clot processing, proteins accumulate in the medium, which bind lactic acid and thereby create the most favorable conditions for the development of microorganisms. Microorganisms, in turn, contribute to the formation of grain.

Hard cheeses should contain a small amount of moisture. This is achieved by processing the cheese - crushing the clot and heating it for the second time, which results in greater dehydration of the grain and its compaction. Stirring the cheese mass prevents the formation of lumps and creates the most favorable conditions for the development of microorganisms.

The second heating, carried out at a temperature of 40°C, creates optimal conditions for the development of most lactic acid microorganisms. A higher temperature (55-59°C) inhibits microbiological processes. There is not only a growth retardation, but also the death of mesophilic lactic streptococci and partially rods. The ratio between lactic acid streptococci and rods is changing. Only thermophilic microbes remain, mostly rods, and then in small quantities. The total content of microbes by the end of the second heating reaches hundreds of millions per 1 g of grain.

Pressing of cheeses is carried out after heating, while the whey is released and the cheese mass is further compacted, in which heat is still retained. The thicker the cheese mass, the larger the cheese, the longer the elevated temperature is kept in it. It is recommended to press the cheese at 18-22°C. This temperature promotes the development of microorganisms, as a result of which their number reaches a billion per 1 g of cheese mass.

The purpose of salting cheeses is to give the product a certain taste, aroma and, in part, texture. Salt regulates microbiological, enzymatic and other processes. Casein after swelling becomes more elastic. The cheese is salted in a concentrated solution of sodium chloride (22-24%) at a temperature of 8-10°C and kept for 6-8 days. Salt promotes the formation of a crust, which prevents the penetration of foreign microflora and thereby protects the product from spoilage. Low temperature (8-10°C) and sodium chloride also slow down the vital activity of lactic acid microorganisms.

Ripening of cheeses. Cheeses after settlements are unfit for consumption. The acquisition of specific properties occurs in relatively warm rooms (cellars), where cheeses are aged (ripen) from 10 days (snack bar) to 8-10 months (Swiss). The taste and smell of cheese is determined by the breakdown products of proteins, milk sugar and fat, which are formed under the influence of enzymes of lactic acid bacteria and rennet. With an increase in temperature, the vital activity of lactic acid bacteria continues. They use milk sugar residues and peptones, products of protein breakdown by rennet. As cheeses ripen, lactic acid bacteria die, first streptococci, and then sticks.

After several months, propionic acid bacteria are included in the process of forming cheeses (Soviet, Swiss), which ferment lactic acid into propionic and acetic acid with the release of carbon dioxide. The gas dissolves in the cheese moisture and, after saturation, forms eyes, and the more gas, the larger their size. In the elastic mass of cheese, the eyes take on a rounded shape and give a certain pattern to the product. In a fragile mass, the eyes have an irregular shape, and sometimes even cracks appear. When bacteria from the group of Escherichia coli (Escherichia) and butyric acid enter the cheese, hydrogen is formed, which does not dissolve in water. The accumulation of gas leads to the appearance of cracks. Thus, according to the drawing on the section of the cheese, to some extent, one can judge the course of microbiological processes.

Cheese defects of microbial origin. Cheese without eyes("blind cheese") - the absence or insufficient amount of propionic acid bacteria. This defect occurs as a result of the death of propionic acid bacteria during heating. The absence of eyes in such cheeses as cheddar, Gornoaltaysky, is not considered a defect.

Cheese with lots of deep eyes. An insufficient amount of lactic acid bacteria leads to the fact that the cheese mass is compacted. In such a mass, gases dissolve poorly and deep eyes are formed. A large number of eyes appear with the premature development of gas-forming bacteria. A contributing factor is the wrong thermal regime.

swelling at the beginning of the ripening process of cheeses, bacteria from the group of Escherichia coli can cause if the medium contains milk sugar. The pattern of cheese on the cut becomes irregular, torn. At the end of the maturation process, when the number of lactic acid bacteria and their products decreases, the pH of the medium increases. In such an environment, butyric acid bacilli can manifest their action, which in the form of spores remain in the curd for a long time. The hydrogen and other gases produced by the bacilli cause the cheese to swell. To prevent swelling, cheese must be made from bacterially pure milk.

Antagonists of butyric microbes - products of lactic streptococci (lowlands), lactic acid bacillus Lactobact. plantarum, etc. Their use in cheese making gives positive results. From silage and manure, you sometimes get into milk. polymyxa is an aerobic bacillus that develops in a low acid environment. It is often the cause of early swelling of Swiss cheese.

Bitter taste. Some lactic acid streptococci (mammococci), found in small amounts in milk and cheeses, decompose proteins and, with their high proteolytic activity, give the cheese a bitter taste. The cheese mass acquires a bitter taste also with a strong development of butyric bacilli. In addition to gas, they form butyric acid.

crust ulceration caused by smallpox mold (Oospora). Ulcerations appear on the surface of the cheese, which sometimes affect the subcortical layer. Microbes can get into the formed voids. With the penetration of putrefactive microbes, the cheese mass is destroyed, it acquires a smearing consistency and a putrid smell. In the voids of the cheese, green penicillium mold often develops. It decomposes fats, the product acquires a bitter taste.

Compliance with technology, sanitary and hygienic conditions of production, careful control over raw materials prevent defects in cheeses and make it possible to obtain a product of good quality.

Questions for self-control: 1. What are the sources of milk contamination?

2 What are the defects of milk?

3 What are the methods of preserving milk?

4. What are the defects of cheeses?

Department of Microbiology, Virology and Pharmacology

Microbiology course

080401 "Commodity research and examination of food products"

abstract

Discipline: Microbiology of food products

On the topic: Microbiology of milk

Milk is the secret of the mammary glands of mammals, physiologically intended for feeding the young. Milk is formed from the constituent parts of the blood by the epithelial cells of the alveoli and is a valuable food product. It contains fatty acids, amino acids, proteins, minerals, vitamins, milk sugar and a large number of enzymes. Nutrients of milk are in the ratio and the form, most favorable for assimilation by an organism. The most complete freshly milked, fresh milk. It has bactericidal properties, i.e., the ability to delay the reproduction of bacteria that enter milk and even kill them. To preserve the bactericidal properties of fresh milk, it is cooled. At a temperature of 30 o C, bactericidal activity lasts for 3 hours, at 15 o C - about 8 hours, at 10 o C - about 24 hours.

Microbes enter the milk from the external environment through the excretory ducts, the milk cistern and the nipple canal. For some of them, milk serves as a good nutrient medium.

Most microbes occur in the nipple canal, milk cistern and less in the excretory ducts and alveoli. Some microbes die under the action of acidic substances, while more resistant micrococci and streptococci remain, which in their properties are close to lactic acid streptococci of intestinal origin. Microbes accumulate at the nipple canal and form a plug, which, along with saprophytes, can contain pathogens of infectious diseases. Usually they are more in the first portions of milk and less in the latter. Therefore, the first portions of milk must be put into a separate container in order to exclude contamination of all milk and the environment. The contamination of milk with microbes depends on the cleanliness and condition of the udder, the skin of the animal, human hands, dishes and other equipment.

Especially many different microbes are found in the milk of animals with mastitis. One of the reasons may be microbes that enter the mammary gland through the nipple canal or by the hematogenous route. Contributing factors are hypothermia, trauma, genetic predisposition. Inflammatory products reduce the quality of milk, while reducing the amount of lactose, calcium, casein. In mastitis milk, staphylococci, streptococci, E. coli and other microorganisms can be found. Their number is largely determined by the state of the external environment.

A large number of microbes are found on the surface of the skin of the animal. The dirtier the skin, the more of them gets into the milk. Thus, according to Backhaus and Congeim, in 1 ml of cow's milk with uncleaned skin, there are from 170 thousand to 2 million microbes, cows with clean skin - 20 thousand. With the systematic cleaning of the animal, their number decreases to 3 thousand in the same volume. Microbes on the surface of the skin come from food, bedding, manure, air.

Feed can be another source of milk contamination: when it is distributed, a lot of dust is generated. Along with the dust, microbes also enter the milk. Therefore, distribution of feed during milking should not be. If old rotten straw is used as bedding, it may contain a large number of microorganisms, especially molds. Scattering such litter before milking increases the number of microbes and their spores both in the air, on the surface of the animal's body, and in milk. In this regard, it is better to use fresh straw, sawdust, shavings, dry leaves or peat as bedding, which absorb moisture, gases and to some extent prevent the development of putrefactive and pathogenic microorganisms. According to A.K. Skorokhodko, Escherichia coli, Salmonella, typhoid bacteria in peat litter die within 6-8 days.

A person can also be a source of contamination of milk with microbes if the rules of personal hygiene are not observed. Therefore, the hands of a milkmaid (milkmaid) must be clean, dry, with short-cut nails.

Microorganisms can get into milk and through the air from animals with tuberculosis, salmonellosis, etc.

The role of flies in the contamination of milk with microbes is enormous. On the surface of their body contains from several thousand to a million microbes, among which there may be pathogens. To combat flies, thorough cleaning, washing, whitewashing, disinfection of farms, milk collection points and the surrounding area are carried out. It is better to clean rooms with a wet method, which significantly reduces the number of microbes, and therefore reduces contamination of milk.

Dishes and milking equipment can also be a source of milk contamination. Therefore, milking machines, used utensils, filters must be kept clean. With machine milking, milk enters a closed system, which prevents microbes from entering it from the outside. However, the poor organization of machine milking leads to a deterioration in the sanitary condition of milk. At the same time, the number of microbes in comparison with manual milking increases by 4-5 times, and sometimes even more. The indicators of the sanitary quality of milk are shown in the following table:

Sanitary quality of milk in the stall keeping of cows (according to E.Sh. Akopyan)

It can be seen from the data in the table that the quality of milk with manual milking was higher than with machine milking. All of the above sources of milk contamination can be minimized or eliminated by observing zoohygienic and other rules in the areas of milking animals and in the process of obtaining the product.

Another type of milk contamination should be noted, which is associated with a new Bacillus species identified by experts from the International Dairy Federation (IMF) and named Bacillus sporothermodurans (Peterson et al., 1996). Bacillussporothermodurans can be isolated from UHT and sterilized whole and skimmed milk, UHT cream, chocolate milk, condensed and reconstituted milk. These heat tolerant spore formers do not alter the stability or sensory characteristics of UHT milk. In all cases where contamination with these bacteria was found after incubation, their total amount in cartoned milk never exceeded a maximum of -150/ml. However, clotting is sometimes noted when such contaminated milk is boiled. Curdling and a pinkish color are due to the long shelf life of milk bottled in plastic bottles. Such packages are a poor barrier to oxygen compared to cardboard ones. The growth of bacteria is possible in milk packaged in various packaging materials: polyethylene, cardboard, Terta-brik and aluminum.

Contamination of UHT and sterilized dairy products with Bacillus sporother modurans is apparently not due to secondary contamination, but due to the survival of spores during the heat treatment process (Hammer et al., 1995). Various sources of pollution can be considered.

The first possible source of Bacillus sporothermodurans is raw milk contaminated on the farm. In 1955, Bacillus sporothermodurans was first detected in raw milk supplied from a farm. In 1966, 100 raw milk samples were analyzed from six different geographic regions. For the detection of Bacillussporothemiodurans, a PCR-based method (polymerase chain reaction) was used. Three samples from the same region gave a positive result at the 100 ml level. These results suggest occasional or local presence and/or very low levels of Bacillus sporothermodurans spore contamination in raw milk. Spores were found in only 2 out of 120 samples of corn silage, grass silage and sugar beet. Therefore, contamination of raw milk on the farm through feed and milking equipment is most likely, but not yet proven.

The reprocessing of contaminated batches of UHT or sterilized dairy products can be considered as a second possible route for Bacillus sporothermodurans contamination. Because spores can survive heat treatment, a single contaminated package containing 103 spores/mL can contaminate a significant proportion of UHT milk during subsequent production.

The third way of contamination is possible during the processing of contaminated milk powder. Hammer et al. (1995) reported the isolation of Bacillus sporothermodurans in milk powder used for processing.

As can be seen, there are many sources of microbial contamination of milk, the composition and number of which change depending on the storage time of the product. In this case, several phases are distinguished.

Antimicrobial (cidic, static) phase characteristic of freshly milked milk, it shows a delay in the growth of microorganisms. Sometimes this phase is called bactericidal, which is not true. According to a number of authors, the antimicrobial substances of milk have a static effect, inhibit the growth of microbes and do not destroy their cells (I. I. Arkhangelsky, P. A. Obukhov). According to other authors, the cidal effect of microbes is noted (A.F. Voitkevich, S.A. Korolev, V.I. Mutovin), and therefore it is more correct to call this phase antimicrobial, which reflects the essence of the issue.

The antimicrobial properties of milk are associated with y- and p-globulins and are determined by the content of lysozymes, lactenins, bacteriolysins, antitoxins, agglutinins and other substances that come from the blood or are synthesized by the mammary gland, V.I. Mutovin explains the antimicrobial properties of milk by the presence of lysozyme M, and in the udder - lysozyme B. Lysozyme M has a wide spectrum of action: it inhibits the growth of both saprophytes and pathogenic microbes. At the end of lactation, it is inactivated. Lysozyme B, although it has a narrower spectrum, but its action is manifested throughout lactation.

UDC…637.1:579

The course of lectures on the microbiology of milk and dairy products was prepared by the professor of the Department of Microbiology, Virology, Epizootology and Veterinary and Sanitary Expertise of the Ulyanovsk State Agricultural Academy, Doctor of Science Vasiliev D.A.

INTRODUCTION.

In this lecture course, in contrast to lectures on the microbiology of meat and meat products, considerable attention is paid to the characteristics of bacteria found in milk and dairy products. This is due to the fact that students study microorganisms contaminating meat and meat products in sufficient detail in the course of microbiology. Lactic acid microorganisms have to be studied in this section of the discipline - “Microbiology of animal products”.

The first scientific studies of lactic acid bacteria were carried out by L. Pasteur; he published the results in 1857. Since then, lactic acid bacteria have attracted the attention of specialists. Based on the use of these microorganisms, large branches of the food industry are created and developed.

In the early 1990s, a new International Standard for the nomenclature of lactic acid bacteria was released. However, given that over the past 10 years reference literature on milk microbiology has practically not been published in the country, the proposed lecture course retains the names of microorganisms used in our country until the 90s, which will allow students to use comparable names of bacteria in the main literature on this issue. Below is a translation table of the names of the main lactic acid bacteria in accordance with the International Standard for Nomenclature.

Nomenclature of lactic acid bacteria

International Standard names Old names

Lac. lactis subsp. lactis str. lactis , Str. Lactis subsp. lactis

Lac. lactis subsp. cremoris str. cremoris

Lac. lactis subsp. lactis str. diacetylactis, Str. acetoinicus

(biovar diacetylactis)

Leuconostoc mesenteriodes Str. citrovorus, Leu.citrovoriim

Leuconostoc mesenteriodes Str. paracitrovorus,

subsp. dextranicum Leuconostoc lactis

Lactobacillus delbrueckii. Lactobacillus lactis

Lactobacillus delbrueckii Lactobacillus bulgaricus

subsp. bulgaricus

Lactobacillus rhamnosus Lactobacillus casei,

Lactobacillus casei subsp. Rhamnosus

Lecture 1. MICROFLORA OF DRINKING MILK

SOURCES OF MILK CONTAMINATION BY MICROORGANISMS

The content of microorganisms in raw milk reflects the level of hygiene of milk production, especially the degree of cleanliness of milking machines, the conditions for its storage and transportation. Two ways of contamination of milk with microorganisms are known: endogenous and exogenous. In the endogenous way, milk is seeded with microorganisms directly in the udder of the animal. Exogenous contamination occurs from external sources: animal skin, bedding materials, feed, air, water, milking equipment and utensils, hands and clothes of dairy farm workers.

endogenous seeding. Udder milk always contains a certain amount of microorganisms. In the glandular part of the udder, microorganisms can be found intermittently and in a single number of cells. In the excretory ducts and milk cistern, the number of bacteria can reach several tens or hundreds of cells per 1 cm. These microorganisms are udder commensals. These include enterococci, micrococci, sometimes mastitis streptococci, corynebacteria, etc.

Udder milk obtained sterile not through the teat canal is called aseptic. It contains a small number of microorganisms - tens to hundreds of cells in 1 cm 3. Old cows have more microbes in their udders than young cows.

A healthy teat canal protects the udder from the external environment due to its anatomical structure. In addition, free fatty acids synthesized by the mucous membrane of the nipple canal have a bactericidal effect. The secret of the nipple channel also contains phospholipids that kill mastitis streptococci and other microorganisms. In case of violation of the protective functions of the teat barrier, microorganisms that are constantly in the teat canal can enter the udder and multiply there.

At the entrance to the teat canal, in the drops of milk left from the previous milking, microorganisms constantly multiply, forming the so-called bacterial plug, in which the number of bacteria reaches hundreds of thousands of cells per 1 cm 3 of milk. Therefore, before milking, the first streams of milk must be milked into a separate bowl, i.e. bacterial plugs should not get into the total mass of milk.

Endogenous seeding of udder milk can also occur with mastitis, septic infectious diseases, injuries and inflammation of the teat canal and udder.

Exogenous seeding. The most important source of bacteria in raw milk is the skin of the animal and especially the skin of the udder and teats, which are worn in the teat cups. The milk film formed during milking between the skin of the teats and the teat cups, the presence of coarse and fine folds on the skin, as well as relatively high temperatures create favorable conditions for the development of microflora. It consists of micrococci, enterococci, Escherichia coli and other saprophytes, as well as pathogenic and undesirable microorganisms for milk production.

It should be strived to ensure that after washing and disinfection before milking, the concentration of microbes on the skin of the udder should not exceed 10 3 microbes per 1 cm 2.

Bedding materials from straw and hay are a significant source of contamination of the skin of the animal, and then milk with E. coli, butyric acid bacteria, enterococci, putrefactive spore-forming yeasts, molds, lactic acid bacteria, etc. Peat crumbs cannot be used as bedding.

Feed also contains a wide variety of micro-organisms. In freshly cut grass there are more lactic acid bacteria, in roughage - putrefactive spore-forming aerobic bacilli. The feed contains propionic acid, acetic acid bacteria, actinomycetes, yeast, etc.

Feeding cows with sour or soil-mixed feed, poor silage or sour bard, combined with existing deficiencies in animal hygiene, leads to contamination of milk with butyric and other bacteria.

Poor-quality feed causes diarrhea in cows, and milk is contaminated with bacteria through the contents of the intestine, 0.1 g of which contains from 10 to 100 thousand bacteria. In the contents of the intestine, the presence of pathogenic and undesirable microorganisms for dairy production is possible.

Salmonella that are often isolated from cows are found only in raw milk, since enterobacteria are destroyed during pasteurization.

Since milk is currently produced and stored predominantly in closed systems, raw milk is contaminated mainly by hand milking. However, when changing milk lines, outside air is always sucked in.

The total number of microorganisms in the air is 300-1500 cells per 1 m 3 .

Water that meets the requirements of GOST for drinking water and is used for washing milk dishes and equipment contains a small amount of microorganisms. The water of open reservoirs or contaminated water contains fluorescent bacilli, coccal microflora, E. coli, putrefactive bacteria, etc. Milking machines and milk storage tanks are the main source of contamination of milk with psychrotrophic bacteria, mainly Pseudomonas. Psychrophilic microbes multiply in a milky-aqueous environment on poorly washed and disinfected facilities, being in the active phase of reproduction. They do not have an adaptation period - lag phase. In poorly washed and not dried equipment, lactic acid bacteria, Escherichia coli, micrococci, putrefactive microorganisms, etc. also multiply.

The hands and clothes of farm workers can become a source of contamination of milk with pathogens (E. coli, staphylococci, streptococci, etc.) of various diseases. Farm workers who come into contact with milk are required to strictly follow the rules of personal hygiene that prevent the contamination of milk with microorganisms.

In raw milk, even if the sanitary and hygienic conditions of its teaching are observed, a certain amount of bacteria is found. If sanitary and hygienic conditions are not observed, milk can be abundantly infected with microbes located on the surface of the udder, falling from the teat canal, from the hands of milkers, milking equipment and utensils, from the air, etc. The total number of bacteria can vary from 4.6 x10 4 to 1.2 x10 6 in cm 3. . The microflora of fresh raw milk is diverse. It contains lactic acid bacteria, mass acid bacteria, groups of Escherichia coli, putrefactive and enterococci, as well as yeast. . There may be pathogens of various infectious diseases (dysentery, brucellosis, tuberculosis, foot and mouth disease) and food poisoning (Staphylococcus aureus, Salmonella, Listeria, Yersinia)

Freshly milked milk contains antimicrobial substances lactenins, lysozymes, etc., which in the first hours after milking delay the development of bacteria in milk. - bactericidal phase. , which decreases with time and the faster, the more bacteria in the milk and the higher its temperature. Freshly milked milk has a temperature of about 35°C. The duration of which is 3 hours, at 10°C - up to 20 hours, at 5°C - up to 36 hours, at 0°C - up to 48 hours. To prolong the bactericidal phase, the milk must be cooled as soon as possible. In milk stored at a temperature below 8-10 ° C, most lactic acid bacteria almost do not multiply, which contributes to the development of cold-resistant psychophilic bakuteria, mainly of the Pseudomonas genus, capable of causing the decomposition of proteins and fat, while the milk acquires a bitter taste. Rancidity in raw milk is also caused by bacteria of the genus Alcaligenes and the spore bacterium Bacillus cereus. At the same time, the total contamination with microorganisms reaches 10 6 - 10 8 bacteria.

Physical and chemical changes in the composition of milk can be associated with the appearance of somatic cells. By origin, these are udder and blood cells. Udder cells are formed in the udder in the process of natural aging and renewal and are an integral part of milk. In the milk of a healthy cow, they make up 60-70% of the total number of somatic cells. The rest is represented by blood cells - leukocytes. Inflammatory phenomena in the udder (mastitis caused by staphylococci) are associated with an increased content of leukocyte somatic cells. Therefore, an overall high level of somatic cells serves as an indicator that milk is obtained from sick cows.

Currently, the determination of the number of somatic cells in milk is recognized worldwide as an indicator of the sanitary state of milk. SanPin 2.3.2.1078-01 sets the upper limits of the allowable content of somatic cells in 1 cm 3 - in milk of the highest orta, no more than 5x10 5, in milk of the first and second grade - no more than 1x 10 6.

To keep it fresh, milk at a dairy farm or collection point is cooled to a temperature of 5-3 ° C and delivered to dairies in a chilled state. They are cleaned of mechanical impurities and impurities, pasteurized or sterilized, cooled, poured into flasks, tetra-packs or other containers and sent for sale.

The purpose of pasteurization is destruction of pathogenic bacteria in it and possibly a more complete reduction in the total contamination of bacteria. Drinking milk is usually pasteurized at 76°C for 15-20 seconds. The mode of pasteurization of milk used for the manufacture of fermented milk products is more stringent. The quality of processing is determined by a negative reaction to phosphatase.

Pasteurization retains a certain amount of vegetative cells of thermophilic and heat-resistant bacteria, as well as bacterial spores. In the residual microflora of milk, mainly lactic acid streptococci of fecal origin (enterococci) are found, in small quantities - spore bacilli and micrococci.

In accordance with SanPiN 2.3.2.1078-01, the amount of MAFAnM in pasteurized milk in consumer packaging should not exceed 1x10 5, in flasks and tanks - 2x10 5 in 1 cm 3. Bacteria of the Escherichia coli group are not allowed in 0.01 cm 3, Staphylococcus aureus - 1 cm 3 (for milk in consumer packaging), in flasks and tanks - 0.1 cm 3, pathogenic microorganisms, including Salmonella and Listeria should be absent in 25 cm 3 Flask milk should be boiled before drinking. Sterilized milk can be stored for a long time, it is not subject to microbial spoilage, since its microflora is destroyed during the sterilization process.

Sterilized condensed milk produced in the form of canned food. The microflora in this milk should be absent, but spoilage of milk is sometimes observed. It manifests itself in the form of swelling (homeless) cans, which is caused by heat-resistant spore-forming anaerobic bacteria Clostridium putrificum, fermenting lactose with the formation of CO 2 and H 2 and butyric acid bacteria. Milk coagulation is caused by heat-resistant aerobic spore bacteria (Bacillus coagulans, Bas. Cereus), which produce an enzyme like rennet.

Condensed milk with sugar also released in hermetically sealed jars, but it is not sterilized. The stability of this product is achieved by an increased content of solids, especially a large amount of sucrose - a high osmotic pressure is created. Micrococci predominate in the microflora of condensed milk, rod-shaped bacteria (often spore-forming (and also yeast) are found in smaller quantities. According to SanPiN 2.3.2.1078-01, 1 g of whole condensed milk with sugar can contain no more than 2x10 4 cells, bacteria of the Escherichia coli group ( BGKP) are not allowed in 1.0 cm 3 .

The most common defect of this milk during long-term storage is the formation of so-called "buttons" - seals of different colors (from yellow to brown). The causative agent of this is chocolate-brown mold of the genus Catenularia. This fungus has a significant proteolytic capacity and can grow with minimal air and high sugar concentration at temperatures above 5°C. Sometimes jar bombing caused by osmotic yeast that ferments sucrose. This reduces the sugar content and increases the acidity.

Powdered milk. Due to low humidity (in sealed containers no more than 4 5, in non-hermetic containers - no more than 7%), it is preserved without microbial spoilage for 8 and 3 months, respectively. In powdered milk of the highest grade there should be no more than 5x10 4 cells, BGKP should be absent in 0.1 cm 3, Staphylococcus aureus - 1.0 cm 3.

Cream. Fresh cream compared to milk is less contaminated with microorganisms, since most of their separation of milk passes into skimmed milk. The composition of the microflora of cream is usually similar to the composition of raw milk. During storage (below 10°C), raw cream may be subject to spoilage similar to the spoilage observed during storage of chilled raw milk.

Pasteurization of cream at 80-87°C (depending on fat content) destroys up to 99% or more of microorganisms. The residual microflora is dominated by thermophilic lactic acid bacilli and bacterial spores.

In accordance with sanitary standards, 1 cm 3 of pasteurized cream should contain no more than 1x 10 5 cells in consumer packaging 2x 10 5 - in flasks; BGKP is not allowed in 0.01 cm 3, pathogenic microorganisms, including Salmonella and Listeria, in 2 cm 3. The shelf life of pasteurized cream is set at 36 hours at a temperature of (4 ± 2) °C.

Dairy products play an important role in human nutrition, since, in addition to nutritional value, they have dietary, and some - medicinal value.

Compared to milk, fermented milk products have an increased shelf life. Besides. they are an unfavorable environment for the development of many pathogenic bacteria. This is due to the increased acidity of the products and the presence of antibiotic substances produced by some lactic acid bacteria.

In the conditions of industrial processing, milk in the manufacture of various fermented milk products is pre-pasteurized and then fermented with specially selected starter cultures from pure or mixed cultures of lactic acid bacteria.

Yogurt (ordinary), sour cream, cottage cheese. These fermented milk products include mesophilic homofermentative lactic streptococci (Streptococcus lactis S. cremoris) and aroma forming streptococci (S. lactis subsp. Diacetilactis).

In the manufacture of cottage cheese, in addition to sourdough, rennet is used, which activates the process.

In the production of amateur sour cream, a mixture of mesophilic streptococcus (S. lactis) and thermophilic (S. thermophilus) is used. Freshly produced sour cream, cottage cheese, liquid sour-milk products, except for thermized ones, when sold in a trading set, are not allowed to be stored for more than 72 hours at a temperature of (4±2) °C. With longer storage, these products can develop psychrophilic yeast, bacteria of the genus Pseudomonas Alcaligenes, molds - microorganisms that enter the product (from production equipment, hands and clothes of workers, from the air. This causes defects in the taste and smell of products, as well as other types damage.

Southern and Bulgarian curdled milk (yogurt). For these yogurt, a symbiotic sourdough is used, containing thermophilic lactic streptococcus ( S.thermophilus ) and Bulgarian stick (Lactobacillus bulgaricus). Bulgarian stick enriches the flavor of curdled milk, and thermophilic streptococcus softens its taste. Bulgarian stick produces antibiotic substances that suppress the putrefactive intestinal microflora. Acidophilic and Bulgarian sticks are active acid-formers, therefore, during short-term storage, the development of psychrophilic bacteria of the genus Pseudomonas, spoilage pathogens, in them is difficult.

The latest regulatory documents in yogurt (GOST R 51331-99) and cottage cheese (GOST R 52096-2003) determine the concentration of starter lactic acid bacteria at the end of storage; 10 6 .

Acidophilic curdled milk a product similar to Bulgarian yogurt: in addition to thermophilic lactic acid streptococcus, acidophilus bacillus is included in the composition of the sourdough.

For acidophilus, a mixture of three starters is used: acidophilus bacillus, starter for cottage cheese and kefir starter in a ratio of 1:1:1.

Kefir In its preparation, not pure cultures of microorganisms are used, but a natural symbiotic kefir ferment - pasteurized milk fermented by the so-called kefir fungus.

Kefir- a product of combined fermentation: lactic acid and alcohol. The alcohol content can reach 0.2-0.6%, the resulting carbon dioxide gives the product a refreshing taste. The latest research by scientists has established that 40% of the microflora of kefir is able to pass through the gastrointestinal tract and conclude that kefir is a probiotic product. In addition, it was found that kefir fungi contain a polysaccharide that has an antitumor effect.

In recent years, a new direction has been developed - the creation of functional fermented milk products that contribute to the maintenance and restoration of human microbial ecology, especially the microflora of the gastrointestinal tract.

According to the international classification, depending on the ability to restore human microflora, it is customary to distinguish products: probiotic, prebiotic and synbiotic.

Probiotic Products contain in their composition live lactic acid bacteria and biphytobacteria - probiotics.

prebiotic products contain in their composition prebiotics - substances that can have a beneficial effect on the human body through selective stimulation of the growth and activity of representatives of the normal intestinal microflora. Thus, due to the action of the enzyme β-galactosidase produced by thermophilic streptococcus on milk sugar, important bifidogenic products are formed that increase the activity of bifidobacteria and stimulate their development.

The most pronounced effect can be obtained by a rational combination of probiotics and prebiotics. Such products are called - synbiotics.

Taking this into account, technological processes have been developed for the production of fermented milk products with bifidobacteria, such as bioyogurt, biokefir, bioryazhenka, biosour cream, etc., produced at the country's dairy plants. An example of another direction is the creation of specialized biologically active additives (BAA) using lactic acid bacteria and their metabolic products. The production of dietary supplement "Acipol" was mastered, which is a mixture of four strains of acidophilus bacillus dried by sublimation and a specific water-soluble polysaccharide of kefir fungus.

Butter is made from pasteurized cream. The number of bacteria in them is usually not large. These are mainly heat-resistant lactic acid bacteria, bacterial spores. The number and species composition of microorganisms in butter depend on the moisture content (plasma) in it and the methods of its manufacture.

Sweet cream unsalted butter contains a variety of microflora. It consists of residual microorganisms (secondary microflora that got into the oil during production from production equipment, from the air during packing and packaging. These are mesophilic and psychrophilic spore and non-spore rod-shaped bacteria, enterococci micrococci, among which many are able to break down milk fat and proteins. Quantity bacteria and varies widely - from a thousand to hundreds of thousands per 1 g, depending on the type of oil.The contamination of the surface layer of the oil block is usually higher than in its thickness.

Sour cream butter is made from pasteurized cream fermented with pure cultures of lactic acid streptococci (S.lactis and S.cremoris). Aromatizing streptococci are also introduced into the starter culture. Naturally, sour-butter, compared to sweet-butter, contains significantly more bacteria, mainly lactic acid, yeast is also present. The number of bacteria in sour cream butter, according to many researchers, reaches millions and tens of millions per 1 g. Extraneous microflora is insignificant; its development is delayed by lactic acid, which is formed by lactic acid bacteria.

Cheese. Cheese properties- taste, aroma, texture, pattern - are formed as a result of complex biochemical processes, in which the main role belongs to microorganisms.

The quality of the finished product is greatly influenced by raw materials - milk, and above all its purity - the degree of contamination with microorganisms undesirable for cheese making. Cheeses are mainly made from pasteurized milk. Coagulation of milk (coagulation of casein) is carried out by fermenting it with lactic acid bacteria and introducing rennet. When developing each cheese, certain technological methods and modes are used. Some of them promote the development of microorganisms, others inhibit their growth.

In the cheese mass, in addition to the starter microflora, there are representatives of the residual microflora of pasteurized milk and microbes that have come from outside. These are groups of Escherichia coli, putrefactive, mayalic, mesophilic and thermophilic lactic streptococci and coli, micrococci, yeast.

The maturation of cheeses proceeds with the active development of microbiological processes. In the very first days of ripening, starter lactic acid bacteria rapidly develop in the cheese, the number of their cells reaches billions. Bacteria ferment milk sugar, with the formation of lactic acid, and some also produce acetic acid, carbon dioxide, hydrogen. Accumulated acids inhibit the development of extraneous microflora.

When maturing hard cheeses with a low temperature of the second heating (such as Dutch), mesophilic lactic streptococci of sourdough (S. lactis, S. cremoris) are of primary importance. as well as non-starter streptococci (S.bovis), representatives of the residual microflora of pasteurized milk. In addition, mesophilic lactic acid bacilli that enter the product during its production are also involved in the process.

By the end of cheese maturation, lactic acid bacteria begin to die off, with streptococci most rapidly. The death of bacteria continues during its subsequent refrigerated storage, but less actively than during maturation.

In the process of maturation of cheeses, changes occur not only in milk sugar, but also in milk proteins. In these processes, lactic acid bacteria play a significant role.

Rennet causes the initial breakdown of proteins - their hydrolysis to peptides. A deeper breakdown - to amino acids, fatty acids, amines - is caused by lactic acid bacteria and their proteolytic enzymes.

Develop in ripe cheeses (especially in Soviet and Swiss) and propionic acid bacteria. They ferment lactic acid (its calcium salt) with the formation of propionic and acetic acids and carbon dioxide gas. The accumulation of carbon dioxide in cheeses as a result of the vital activity of lactic acid bacteria causes the formation of cheese “eyes”, which create the pattern of the cheese.

During the maturation of hard cheeses, especially at the initial stage of the process, bacteria of the Escherichia coli group can actively develop, and at the end of ripening - butyric. The growth of these bacteria is accompanied by an abundant release of gases (carbon dioxide and hydrogen), which creates an irregular pattern, cracks and even swelling of the product. The consistency of cheese changes, an unpleasant smell and a sweetish taste, as well as bitterness.

Significantly reduces the quality of cheese an anaerobic spore bacterium - Clostridium putrificus, which has a pronounced proteolytic activity. At the same time, the cheese softens, its consistency becomes smeared, a putrid smell and an unpleasant taste appear .. However, spoilage, especially of hard rennet cheeses, is more often manifested in foresting. Fungi of the genus Penicillium develop, and others (Asporgillius, Cladosporium) also occur. Smallpox mold - Oospora causes crusting. Molding not only does not reduce the commercial appearance of cheese, but also changes in protein substances, TV and fat. Many types of mold are capable of toxin formation. Removing mold from a surface does not guarantee the absence of toxins in the product. One of the sources of infection of cheeses with molds is the chambers for ripening and storing cheeses. The air, walls, racks, the surface of air conditioners are always contaminated with molds to one degree or another. Measures - ozonation and treatment with UV rays., treatment with solutions of sorbic acid - 05-1% (or potassium sorbate) of the surface of cheeses. Covering cheeses with dense films - to create anaerobic conditions against molds.

Production of mold cheeses- which, in addition to lactic acid bacteria, infect with special molds. The peculiarity of the taste of these types of cheese is due to a change not only in milk sugar and protein substances, but also in milk fat, which is broken down by molds with the formation of volatile fatty acids.

In the production of Snack Cheese, filamentous fungi Penicillium candidum and P. camembetti are used (by spraying the surface). In addition to molds, yeasts develop on the surface of the cheese, which have a proteolytic effect.

During the ripening of Roquefort cheese, R. Rogueforti participates. The spores of the fungus are introduced into the cheese mass. To create favorable aerobic conditions for the growth of the fungus, the cheese head is pierced throughout its thickness. During the maturation of cheese, the surface microflora, which includes yeast, micrococci and rod-shaped bacteria, also plays a positive role.

In the production of some cheeses with mucus on the surface (for example, Lithuanian), in addition to the starter microflora, the mucus surface microflora, consisting of lactic acid bacteria, yeasts, micrococci and proteolytic rod-shaped bacterium, whose vital products give the cheese a specific taste, is of great importance for cheese maturation.

Processed cheeses produced mainly from mature cheeses. Their microflora is represented mainly by spore-bearing bacteria; there are micrococci and lactic acid bacteria preserved during the melting of cheese. The number of bacteria in these cheeses is relatively small - a thousand cells per 1 g. During refrigerated storage (up to 4 ° C), significant changes in the microflora are not observed for a long time. Yeast and mold spores are found in the surface microflora. At higher storage temperatures, the number of bacteria increases more or less rapidly depending on the temperature. Butyric acid bacteria are the most dangerous cause of cheese swelling. To avoid this type of spoilage, the antibiotic nisin is introduced into cheeses. Freshly made processed cheeses without fillers are considered satisfactory if they contain no more than 5x10 3 CFU per 1 g, no more than 50 molds and yeasts, BGKP should be absent in 0.1 g (SanPiN 2.3.2.1078-01.

The total bacterial contamination of smoked sausage cheeses usually does not exceed hundreds of cells per 1 g. These are mainly spore bacteria capable of proteolysis and lipolysis. The main type of spoilage of these cheeses is molding.