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MINISTRY OF EDUCATION OF THE RUSSIAN FEDERATION

Kemerovo Technological Institute of Food Industry

MICROBIOLOGY MILK And MOLO H NYH

ETC O DUKTOV

EducationalPaboutsobie

And.BUT.yeryomine

Kemerovo 2004

UDC 637.1: 579

Published by decision of the Editorial and Publishing Council

Kemerovo Technological Institute of Food Industry

Reviewers:

Candidate of Technical Sciences, Associate Professor of the Kemerovo Institute (branch) RGTEU O.S. Gabinskaya;

Candidate of Agricultural Sciences, Associate Professor of the Kemerovo Agricultural Institute L.G. Pinchuk.

Eremina I.A.

Microbiologymilkanddairyproducts: Tutorial. - Kemerovo, 2004. - 80 p.

The textbook is compiled in accordance with the state educational standard of higher vocational education direction 6556900 - "Technology of raw materials and products of animal origin" for the specialty 271100 "Technology of milk and dairy products".

The role of microorganisms in the formation of the quality of dairy products is shown, their biological properties, as well as microbiological processes caused by technically important microflora, pathogenic and opportunistic microorganisms are considered.

The basic principles of microbiological control of the production of various groups of dairy products are outlined.

Content

• ChapterI. The main representatives of the microflora of milk and the processes they cause
• ChapterII. Special microbiology
• Topic 4. Microbiology of raw and pasteurized milk
• Topic 5. Microbiology of starter cultures and fermented milk products
• Topic 6. Microbiology of butter
• Topic 7. Microbiology of cheeses
• Topic 8. Microbiology of canned milk and ice cream
• Topic 9. Microbiology of dairy by-products
• List of recommended literature
• Dictionary of Latin names of microorganisms

Section I. The main representatives of the microflora of milk and the processes they cause

Milk is a good nutrient medium for the development of most microorganisms, both introduced with starter cultures and those entering it from outside.

During the processing of milk in the production of dairy products, the main role is played by the following processes:

· processes splitting lactose through monosugar and pyruvic acid carried out by lactic acid and propionic acid bacteria, bacteria of the Escherichia coli group, yeast and other microorganisms.

· processes splitting dairy squirrel (casein), carried out by lactic acid and proteolytic bacteria, micrococci, yeasts and microscopic fungi.

· Processes decomposition dairy fat occurring as a result of the development of psychrophilic lipolytic microorganisms and microscopic fungi.

All microorganisms found in milk and dairy products dependencies from them roles in formation quality dairy products can be divided into 3 groups:

1 . Technicallyimportantmicroflora. It is divided into useful microaboutflora(microflora of starter cultures: lactic and propionic acid bacteria, bifidobacteria, yeast, acetic acid bacteria) and technically harmful microflora(microflora that causes defects in dairy products).

Some representatives of technically important microflora can play both a positive and a negative role in shaping the quality of dairy products. So, lactic acid bacteria are involved in the process of fermentation of milk, but can also cause souring of the product; yeast is involved in the maturation of kefir and koumiss, acidophilus-yeast milk, however, their development in other products, as well as excessive reproduction in the above products, leads to their swelling; acetic acid bacteria are part of the microflora of kefir fungus and contribute to the formation of a typical taste of kefir, but at the same time they can cause defects in the taste and texture of cottage cheese.

Other representatives of technically important microflora play only a negative role in the production of dairy products (for example: microscopic fungi, psychrophilic and spore-forming bacteria).

2 . Pathogenicandconditionally pathogenicmicroorganisms cause foodborne illness.

Pathogenic microorganisms- pathogens of infectious diseases (brucellosis, tuberculosis, foot-and-mouth disease, etc.) do not multiply in milk and dairy products, but can remain viable for a long time. Of the pathogenic microorganisms in all dairy products, the presence of salmonella is normalized.

Conditionally pathogenic microorganisms are causative agents of food poisoning: toxicoinfections and intoxications. Many opportunistic microorganisms (for example, Bacillus cereus, Clostridium perfringens, Staphylococcus aureus) can multiply in dairy products, affecting their organoleptic characteristics and accumulating toxins. In many dairy products, the presence of Staphylococcus aureus is determined to assess their quality.

3 . Microorganisms - indicatorssanitaryconsistInia

In our country, bacteria of the Escherichia coli group (ECG) have been chosen as sanitary indicative microorganisms for assessing the sanitary condition of milk and dairy products. According to the content of BGKP, the degree of contamination of products with human secretions and, therefore, the degree of their epidemiological danger to the consumer is judged. Therefore, the presence of BGKP is normalized for all dairy products without exception.

The sanitary condition of dairy products that do not contain technically useful microflora can also be judged by the number of mesophilic aerobic and facultative anaerobic microorganisms (QMAFA n M) in them.

Topic 1. Representatives of technically useful microflora and the processes they cause

1.1 Lactic acid bacteria

1.2 Yeast

1.3 Acetic acid bacteria

1.4 Propionic acid bacteria

1.5 Bifidobacteria

1.1 Lactic acidbacterii

Systematic belonging lactic acid ba to terium

In accordance with the Bergi classification of bacteria, lactic acid bacteria belong to the kingdom of prokaryotes, the division of scotobacteria, the class of true bacteria (Eubacteriales), to the families Streptococcaceae (lactic acid streptococci) and Lactobacillaceae (lactic acid bacilli).

The Streptococcaceae family includes the genus Streptococcus and Leuconostoc.

Lactic acid bacteria of the genus Streptococcus are widely used in the production of cottage cheese, sour cream, fermented milk drinks and other products. This genus includes the following species: Streptococcus lactis, Streptococcus cremoris, Streptococcus diacetylactis, Streptococcus acetoinicus, Streptococcus thermophilus. All lactic acid streptococci are gram-positive, have spherical cells, are located depending on the species in pairs, short and long chains.

Of the Leuconostoc genus, only Leuconostoc cremoris, Leuconostoc lactis and Leuconostoc dextranicum are used in the dairy industry. These bacteria, like streptococci, have spherical cells connected in pairs or chains. Many representatives of the genus Leuconostoc form capsules, therefore, during their development on sugar-containing media, mucus is formed.

Until recently, in our country, lactic acid bacilli were usually assigned to the Lactobacterium family (according to Krasilnikov's classification proposed in 1949). However, in the modern Bergi bacteria guide, these microorganisms are assigned to the Lactobacillaceae family, the genus Lactobacillus. Morphologically, these bacteria are rod-shaped, arranged singly, in pairs, or in chains. Gram-positive, spores and capsules do not form.

All lactic acid bacteria cause lactic acid br about ing - ferment lactose and glucose to lactic acid. A feature of lactic acid bacteria is the presence of enzymes in them : -galactosidase hydrolysis of lactose to glucose and galactose, and lactate dehydrogenase, which reduces pyruvic acid, formed during glycolysis, into lactic acid. Depending on the type of pathogen, there are two forms lactic acidfermentation: homo farmntative and heterofermentatyinnoe.

At homofermentative lactic acid fermentation The final product is lactic acid:

C 6 H 12 O 6 2 CH 3 CH 2 OUN E

glucose lactic acid

The causative agents of homofermentative lactic acid fermentation include the following lactic acid bacteria: Streptococcus lactis, Streptococcus cremoris, Streptococcus thermophilus, Lactobacillus bulgaricus, Lactobacillus lactis, Lactobacillus acidophilus, Lactobacillus helveticus, Lactobacillus casei, Lactobacillus plantarum.

At heterofermentative lactic acid fermentation a number of end products are formed (lactic, succinic, acetic acids, ethyl alcohol, carbon dioxide, molecular hydrogen):

C 6 H 12 O 6 CH 3 CH 2 OUNOH UNOHSN 2 CH 2 COOH

glucose lactic acid succinic acid

CH 3 COOH CH 3 CH 2 OH CO 2 H 2 E

acetic acid ethyl alcohol

The causative agents of heterofermentative lactic fermentation are: Streptococcus diacetylactis, Streptococcus acetoinicus, Lactobacillus brevis, Lactobacillus fermentum, all species of the genus Leuconostoc.

Lactic acid bacteria have different enzymatic activities in the fermentation of lactose. The most active acid formers are Streptococcus lactis, Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus helveticus.

Role major species lactic acid bact e riy in formation quality dairy produ to Comrade

Microorganisms	Products for the production of which they are used	The vices that cause
Streptococcus lactis	Cottage cheese, sour cream, drinks with fruit and berry fillings	Atypical taste, flabby texture of acidophilic products, souring of pasteurized milk, cream
Streptococcus cremoris	Cottage cheese, sour cream
Streptococcus diacetylactis, Streptococcus acetoinicus	Cottage cheese, sour cream, sour cream butter	Stimulate the development of heat-resistant lactic acid sticks - causative agents of the defect "excessive acidity"
Streptococcus thermophilus	Ryazhenka, Varenets, yogurt	Atypical taste and texture
lactobacillus acidophilus	acidophilus, acidophilus milk, dairy products for children	Excessive acidity during slow cooling after fermentation
Leuconostoc cremoris	Cottage cheese, sour cream	Lose activity in spring time
Leuconostoc dextranicus		Swelling of kefir with active development

Physiological properties lactic acid bact e riy

All lactic acid bacteria are facultative anaerobes, acidophiles. Most lactic acid bacteria are mesophilic, i.e. the optimum temperature for their development is 30 0 C. Thermophiles (T opt 35-40 0 C) include the following lactic acid bacteria: Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus helveticus, Lactobacillus lactis, Lactobacillus bulgaricus.

Lactic acid bacteria are very demanding on the nutrient medium. They need a complete set of amino acids, B vitamins, nucleic acid components (purine and pyrimidine bases). natural habitat lactic acid bacteria are the surface of plants, the gastrointestinal tract, milk and dairy products, places of decomposition of plant residues, manure, etc.

1 .2 Yeast

Systematic owned and ness yeast

Yeasts are higher fungi that have lost the ability to form mycelium and have turned into unicellular organisms.

They belong to the kingdom of eukaryotes, the department of true fungi, most yeasts are representatives of two classes: ascomycetes and deuteromycetes. In addition, yeasts are divided into sporogenic and asporogenic. In milk and dairy products, sporogenic yeasts of the Saccharomycetaceae family (for example, the genera Saccharomyces, Zygosaccharomyces) and asporogenic yeasts of the Torulopsidaceae family (the genera Torulopsis, Candida, Mycoderma, etc.) are most often found.

The classification of yeast is based on the following features: differences in the nature of their vegetative propagation, the ability to spore formation and sexual reproduction, as well as other morphological and physiological properties.

Many yeasts are pathogens alcohol fermentation e nia - the process of anaerobic oxidation of sugars to ethyl alcohol:

C 6 H 12 O 6 2CH 3 CH 2 OH 2CO 2 E

glucose ethyl alcohol

The ability of yeast to multiply in milk and dairy products is determined by their ability to ferment or oxidize lactose, as well as the presence of microflora in milk with β-galactosidase activity (see clause 1.1.). In this regard, the yeast found in milk and dairy products are divided into 3 gruePpy:

· Yeast, not capable to alcohol fermentation but Paboutconsuming lactose by direct oxidation (grow in milk, but lactose is not fermented). Such yeasts include yeasts of the genera Mycoderma, Torula.

· Yeast not fermenting lactose but fermentandwaving other Sahara. These yeasts can only develop in co-culture with microorganisms that have β-galactosidase activity and hydrolyze milk sugar to glucose and galactose. Such yeasts are most of the yeast species of the genus Saccharomyces.

· Yeast, fermenting lactose. There are not many such yeasts. The following yeast species of this group are most often found in dairy products: Saccharomyces lactis, Saccharomyces fragilis, Torulopsis kefir, Torulopsis sphaerica, Candida pseudotropicalis, etc.

fizi about brain teaser properties yeast

Most yeasts are facultative anaerobes, some yeasts are aerobes. They grow well in an acidic environment (acidophiles). In relation to temperature, yeasts are mesophiles, since the optimum temperature for their development is 25-30 0 C. Higher temperatures stimulate the development of Torulopsis sphaerica yeast and lactose-free yeast. Hexoses, other carbohydrates, alcohols, organic acids are best used as a carbon source. The sources of nitrogen for them are ammonium salts, amino acids, peptides.

natural habitat yeast is the surface of fruits and berries, juice and surface of leaves, nectar, water, soil, skin and digestive tract of people and animals. There are pathogenic and opportunistic forms of yeast that cause candidiasis.

Role yeast in formation quality dairy etc about ducts exceptionally large. They are used in the production of kefir and koumiss, being not only causative agents of alcoholic fermentation, but also producers of B vitamins, antibiotic substances that suppress the development of tubercle bacillus and other pathogenic microorganisms. The waste products of yeast activate the development of lactic acid bacteria. Some yeasts are used in the production of butter, as they prevent the development of microscopic fungi on its surface and thus increase the stability of the oil during storage.

On the other hand, yeast is a pest in the production of many dairy products.

Intensive development of yeast of non-starter origin often leads to swelling, a change in the taste of cottage cheese, sour cream, sweet curd products, abundant gas formation of condensed milk with sugar (bombing cans), the appearance of an alcohol taste and smell, as well as swelling of cheeses.

1.3 UksuWithbut sourbacteria

Systematic belonging acetic bact e riy and them morfol about logical properties

They belong to the genus Acetobacter, which includes 11 species, the type of which is Acetobacter aceti.

Acetic acid bacteria (acetobacteria) isolated from dairy products are mobile gram-negative rods that are arranged singly, in pairs, in chains. Spores and capsules do not form.

Acetobacteria carry out acetic acid fermentation - oxidation of alcohol under aerobic conditions to acetic acid:

CH 3 CH 2 OH O 2 CH 3 COOH H 2 O E

ethyl alcohol acetic acid

Physiological properties uksu With acidic bacteria

Acetic acid bacteria are strict aerobes. The optimum growth temperature is 30 0 C, the temperature limits of development are 5-42 0 C. Acidophiles (optimum pH 5.4-6.3, but can grow at pH 4.0-4.5). Grow on simple and complex nutrient media, most strains do not need vitamins. Ethanol and lactic acid are good carbon sources.

Able to oxidize lactic and acetic acid to carbon dioxide and water (over-oxidation). Many amino acids also oxidize well, they do not hydrolyze lactose.

Pigments do not form, but the cell mass may be pink due to the presence of porphyrins; some strains produce a brown, water-soluble pigment.

On liquid acidified media form a film. In milk, they develop poorly and do not form acids.

microbiology milk dairy product

habitat : on fruits, vegetables, sour fruit juices, vinegar, alcoholic beverages.

Role acetobacteria in formation quality dairy etc about ducts can be both positive and negative.

On the one hand, acetic acid bacteria are part of the natural symbiotic starter for kefir and give kefir a specific taste and aroma with moderate development.

On the other hand, the development of these bacteria in sour cream, cottage cheese, yogurt leads to the appearance of an undesirable smell and taste of acetic acid and mucilage of the product.

1 .4 propionic acidbatotheories

Systematic belonging propionic acid bacteria and them morphological its th stva

Propionic acid bacteria belong to the family Propioni-bacteriaceae, the genus Propionibacterium, which includes 8 species.

In the dairy industry, in particular in cheese making, Propionibacterium shermanii is most often used.

Propionic acid bacteria are small immobile polymorphic rods that do not form spores and capsules.

Cells may be coccoid, elongated, bifurcated, or branched. Arranged singly, in pairs, in short chains, in the form of the letters V or Y, or in the form of Chinese characters

propionic acid bacteria are the causative agents etc about peony about sour fermentation - the process of fermentation of monosaccharides, lactic and malic acids, glycerol, peptones and other substances into propionic and acetic acids, carbon dioxide and water:

3C 6 H 12 O 6 4CH 3 CH 2 COOH 2CH 3 COOH 2CO 2 2H 2 O E

glucose propionic acid acetic acid

Physiological its th stva

Propionic acid bacteria are facultative anaerobes: they can grow under both aerobic and anaerobic conditions, although most strains grow better under strictly anaerobic conditions. Optimum growth is observed at a temperature of 30-37 0 C and a pH of about 7. For their growth, they require the presence of vitamins (pantothenic acid, thiamine and biotin), proteins, amino acids in the medium, but they can also develop on media with the introduction of inorganic nitrogen compounds (for example, ammonium salts). In milk, propionic acid bacteria develop slowly and coagulate it after 5-7 days.

habitat : gastrointestinal tract of ruminants, milk and dairy products.

Role in formation quality t wa dairy products

They are used in the production of hard cheeses with a long ripening period: they ferment lactic acid, which is formed during the fermentation of lactose by lactic acid bacteria, into propionic and acetic acid. These acids give cheeses their tangy taste, and the carbon dioxide produced during fermentation forms the cheese's texture. In addition, propionic acid bacteria, being active producers of vitamin B 12, enrich cheeses with this vitamin.

1 .5 bifidaboutbacteria

Systematic belonging beef and prebacterium, them morphological and physiological its th stva

Bifidobacteria belong to the family Actinomycetaceae, the genus Bifidobacterium, which includes more than 20 species. The type species is Bifidobacterium bifidum.

Bifidobacteria are extremely variable small rods - straight, curved, branched, forked V - or Y-shaped, club-shaped, spatulate. Gram-positive, spores and capsules do not form.

In relation to oxygen, bifidobacteria are strict anaerobes, however, in the process of cultivation, they acquire the ability to develop in the presence of a small amount of oxygen. The optimal temperature is 36-38 0 С, the temperature limits of growth are 20-50 0 С. The optimal value of active acidity is 6-7.

Bifidobacteria are cultivated in milk, hydrolyzed milk or casein hydrolyzate, as well as in liver broth with the addition of growth substances (yeast autolysate, corn extract, cysteine, etc.).

Most strains of bifidobacteria do not ferment milk or ferment it after 4 days or more. However, in the process of cultivation, the biochemical activity of these bacteria increases and milk coagulation occurs after 24-36 hours.

Bifidobacteria ferment glucose, galactose, fructose, lactose, etc. When glucose is fermented, acetic, lactic acids, a small amount of formic and succinic acids are formed.

habitat : Bifidobacteria are obligate intestinal microflora.

Perform row useful for organism fun to tions :

· Have a positive effect on the structure of the intestinal mucosa and its adsorption capacity;

Actively synthesize vitamins of group B, ascorbic acid, vitamin K;

Form some essential amino acids from inorganic nitrogen compounds (for example, alanine, valine, asparagine);

Create an acid reaction in the intestines;

· Possess antagonistic activity against pathogenic microorganisms - causative agents of intestinal infections;

Promote better absorption of calcium salts, vitamin D, iron.

In connection with the foregoing, bifidobacteria are currently found wide application in the creation of new dairy products for children and preventive nutrition, and are also used as probiotics for animals, as they contribute to the normalization of the intestinal microflora.

Questions for self-test R ki

1. What is systematic belonging lactic acid batoterium?

2. Describe morphological properties lactic acid streptococci, leuconostocs, lactic acid Palocks.

3. AT how difference homofermentative lactic acid fermentation from getheroenzymatic?

4. List kinds homofermentative lactic acid bacteriy.

5. What kind kinds heterofermentative lactic acid bacteria To you andhknown?

6. Where inhabit lactic acid batotheories?

7. What is role lactic acid bacteria in formation toaqualities dairy produtoComrade?

8. What kind yeast meet in milk and dairy produtomax?

9. On the what kind groups share yeast in dependencies from ableaboutsti ferment latotosu?

10. What is role yeast in formation quality dairy etcaboutducts?

11. AT what product acetic bacteria are included in compound Paboutuseful microflaboutry?

12. What is role propionic acid bacteria in formation qualityestva youRbreath cheeses?

13. List morphological and physiological properties bifidobacteriy.

14. What role perform bifidobacteria in organihme?

Topic 2. Representatives of technically harmful microflora and the processes they cause

2.1 Putrefactive bacteria

2.2 Microscopic fungi

2.3 Bacteriophages

2 .1 putridbacterii

rotting ( ammonification ) - the process of deep decomposition of proteins by microorganisms.

The decomposition of proteins occurs in steps:

· Under the action of extracellular proteolytic enzymes, proteins are cleaved first to peptones, then to polypeptides and then to amino acids;

· The resulting amino acids diffuse into the cells and can be used for both constructive and energy metabolism.

Split amino acids happens through deaminersania(cleavage of the amino group with the release of ammonia) and decarbotosilyation ( cleavage of the decarboxylic group with the release of carbon dioxide). As a result, organic acids are formed (for example, butyric, acetic, propionic, hydroxy and keto acids), as well as high molecular weight alcohols.

In the future, the formation of end products depends on the conditions of the process and the type of microorganism that causes decay.

Aerobic decay

Occurs in the presence of oxygen. The end products of aerobic decay are, in addition to ammonia and carbon dioxide, water, as well as hydrogen sulfide and mercaptans (which have the smell of rotten eggs).

An a aerobic decay

Occurs under anaerobic conditions. The end products of anaerobic decay are the products of decarboxylation and deamination of amino acids: indole, cresol, phenol, skatole (bad smelling substances), diamines, the derivatives of which are cadaveric poisons and can cause food poisoning, as well as ammonia, carbon dioxide.

pathogens decay

The most active causative agents of decay are bacteria. Among them there are spore-forming and non-spore-forming, aerobic and anaerobic bacteria. Most of them are mesophiles, but psychrophiles and thermophiles are also found. Many putrefactive bacteria react negatively to the acidic reaction of the environment and the content of table salt in it.

Putrefactive bacteria are widespread in nature: they are found in soil, water, air, the intestines of humans and animals, and on food products.

Vozb at parents aerobic decay

Aerobic spore-forming bacteria belong to the family Bacillaceae, genus Bacillus. These are Gram-positive rods that produce heat-resistant spores. Sticks, depending on the type, can be located singly, in pairs and in chains. Bacillus subtilis, Bacillus polymyxa, Bacillus megaterium, Bacillus coagulans, Bacillus stearother-mophilus are most often found in milk and dairy products. Many aerobic spore-forming bacteria cause defects in dairy products (bitter taste, premature coagulation of milk without increasing acidity, etc.).

Non-spore facultative anaerobic putrid bacterii represent the family Enterobacteriaceae of the genera Proteus (Proteus vulgaris) and Ecsherichia (Ecsherichia coli). They are Gram-negative, non-spore-forming rods that are singly arranged. Capsules do not form. They cause defects in dairy products: impure taste, bitter taste, brown spots on the rind of Dutch cheese, etc.

Non-spore putrid pigment-forming bacteria species Pseudomonas fluorescens (fluorescent stick), Pseudomonas aerogenosa (pseudomonal stick), Serratia marcescens (wonderful stick). They are Gram-negative rods and do not form spores or capsules. They are located singly. Psychrophiles.

They cause color defects, change the taste and smell of dairy products during long-term storage in a chilled state.

pathogens anaerobic decay belong to the family Bacillaceae, genus Clostridium (butyric acid bacteria).

The following species are most commonly found in milk and dairy products: Clostridium perfringens, Clostridium putrificum, Clostridium sporogenes, Clostridium butiricum, Clostridium subterminalis. These are large, mobile gram-positive rods that form resistant spores.

When spores are formed, the cells take the form of a spindle (if the spores are located in the center of the cell) or the shape of a drumstick. Sticks can be arranged singly and in chains.

The main feature of butyric acid bacteria is that they belong to strict (obligate) anaerobes, i.e. can grow and develop only without access to air (oxygen is a poison for them).

Clostridium causes defects in the taste, smell and texture of dairy products. So, in the production of cheeses, these microorganisms cause their late swelling: the cheese acquires an irregular slit-like pattern, a softened, spongy texture, and an unpleasant greasy smell.

In addition to the fact that clostridia actively decompose proteins, they are pathogens butyric fermentation - anaerobic oxidation organic matter(carbohydrates, alcohols, amino acids) into butyric acid:

C 6 H 12 0 6 CH 3 CH 2 CH 2 COOH 2CO 2 H 2 E

glucose butyric acid

Butyric acid gives dairy products a rancid taste, and the gases formed (carbon dioxide, molecular hydrogen) cause bombing of canned milk cans.

2.2 Microscopeandcalmushrooms

Microscopic fungi are widely distributed in the production of dairy products. They cause molding of products during storage.

The most common microscopic fungi of the following genera: Oidium (Oidium lactis), Aspergillus, Penicillium, Alternaria, Cladosporium, Catenularia.

Mushrooms belong to the kingdom of eukaryotes, the kingdom of Mycota (Mycetes), the department of true fungi.

Mushrooms are aerobes, but can also grow in the depth of the product in the presence of voids and minimal air access. Mesophiles, but can develop in a very wide temperature range (thermotolerant), for example, at low temperatures - from 5 to 2 0 C. They are acidophiles, tk. prefer an acidic environment. Mushroom spores die during pasteurization of milk, but are resistant to disinfectant solutions.

All microscopic fungi actively decompose proteins (see item 2.1) and milk fat.

Oxidation fat microscopic mushrooms begins with the hydrolysis of fat under the action of lipolytic exoenzymes to glycerol and higher fatty acids. This process does not provide the microorganisms with energy, so the resulting hydrolysis products are used as an energy material. The process of oxidation of glycerol and higher fatty acids occurs only under aerobic conditions. Glycerin quickly oxidizes to carbon dioxide and water. Oxidation of higher fatty acids is slow. During the oxidation process, intermediate products are formed: ketones, aldehydes, hydroxy acids, which give the oxidized fat a rancid taste.

Some fungi in the process of growth on food products form toxic substances: myco- and aflatoxins, therefore, they can be causative agents of food intoxication.

Some Penicillium species such as Penicillium roqui-forti, Penicillium camamberti, Penicillium candidum are called "noble molds". They are used in the production of some types of soft cheeses, giving the cheese a peculiar taste due to the change in milk sugar, proteins, milk fat and the formation of volatile fatty acids.

2.3 Bacteriophagi

Bacteriophages are viruses of bacteria. They do not have cellular structure, and the size of their particles is measured in nanometers (1 nm=10 -9 m). Bacteriophages are composed of a nucleic acid covered with a protein coat. They have a club-like shape. The main property of bacteriophages is their specificity.

Phages are resistant to high temperatures. They withstand milk pasteurization at 75 0 С for 15 seconds.

They tolerate freezing and long-term storage (for years) in dried substrates.

Phages are highly sensitive to acids. Ultraviolet irradiation and ionizing radiation cause their inactivation, and at lower doses - mutations.

Bacteriophages cause lysis (dissolution) of bacteria used in the production of dairy products, as a result of which the terms of product development increase and its quality deteriorates.

In the production of fermented milk products, the most important are phages that infect mesophilic lactic streptococci: Streptococcus lactis, Streptococcus cremoris, Streptococcus diacetilactis. Bacteriophages that infect Streptococcus thermophilus and lactic acid bacilli have been found. However, among these microorganisms, bacteriophages are very rare.

Distinguish 2 kind phages: vir at tape andmoderate .

When exposed virulent phage its development cycle in the cell ends with cell lysis and the formation of phage progeny.

When cells are infected moderate phages(Prophages) the nucleic acid of the phage is integrated into the genetic apparatus of the cell without harming it. When bacteria multiply, not only the DNA of the cell is synthesized, but also the nucleic acid of the phage. The progeny of a cell containing a prophage is called lysogenic cult at Roy . Under the action of external factors on a lysogenic culture, a temperate phage can become virulent and cause lysis of bacterial cells.

Lysogenic strains of lactic acid bacteria are permanent habitat bacteriophages and the main source of their entry into production. Sources of infection of production with bacteriophages are also milk, starter cultures, fermented milk products, equipment, air, whey.

Main conditions, conducive development bacteriofagi, are: continuous maintenance of the technological process; acid reaction of the medium, addition of CaCl 2 ; spraying serum; mixing.

Main way warnings development ba to theriophage :

· Maintenance aseptic conditions at production starter cultures. Aseptic production of starter cultures provides for absolute sterility, sufficiently high heating of milk (carried out at a temperature of at least 90 0 C), the most thorough washing and disinfection of all installations for the production of starter cultures.

· Frequent change starter cultures. Starter cultures should be used within a few days and then starter cultures with similar properties should be used. For a shift, you need to have from 3 to 8 starter cultures.

· alternation in leaven strains insensitive to big quantity types bacteriophagov.

· Exception from starter cultures landsogenic strains.

· Application nutritional environments, inhibitory development bacteriaaboutphage. Based on the fact that the virulence of phages depends on the presence of calcium. This is due to the fact that the particles of phage and bacteria have the same electric charge and in the absence of calcium ions they repel each other.

· Addendum in Wednesday immune milk, those. milk obtained from cows immunized with bacteriophages and containing specific anti-phage antibodies.

· Prevention splashing wheytki.

· Careful washing and disinfection equipment, walls premises solutions chloride IzveWithti.

Questions for self-test R ki

1. What such decay? How leakedano this process?

2. What present yourself processes deamination and soundboardRboxing amineaboutacids?

3. What kind final products arrazuyutsya at aerobic rotting?

4. List products, which formed in result enaaerobic decay?

5. What kind putrid spore-forming aerobic bacteria To you andhknown?

6. rotting what kind cause indisputable facultative anaerobic putrid bacterii?

7. What chemism butyric fermentation? Describe microorganisms-excitationandbodies this process.

8. What kind microscopic mushrooms more often Total meet in they sayaboutke and dairy products? What kind processes they inscall?

9. How way leaks process oxidation fat microskaboutpeak mushrooms?

10. What such bacteriophages? AT how difference virulent and mindefinancial phages?

11. To give definition " lysogenic culture" batoterium.

12. List main way warnings development phages in production milk and dairy etcaboutducts.

Topic 3. Pathogenic, conditionally pathogenic, sanitary-indicative microorganisms

3.1 Pathogenic microorganisms - causative agents of infections. Chemical composition and properties of microbial toxins

3.2 Conditionally pathogenic microorganisms - causative agents of food poisoning. Food poisoning (toxicosis)

3.3 Microbiological quality control of dairy products

3.1 Pathogenicmicroorganisms - pathogensinfetotions.

Chemicalcompoundandpropertiesmicrobialtoxandnew

The causative agents of infectious diseases are pathogenic microorganisms.

Main properties P a togenic microbes are :

· pathogenicity- the potential ability of a microorganism of a certain type to take root in a macroorganism, multiply in it and cause a certain disease. Pathogenicity is a species characteristic of pathogenic microorganisms. To assess and compare the pathogenicity of individual strains of pathogenic microbes, the concept of " virulence" - the degree of their pathogenic effect. Virulence is not a constant feature of pathogenic microbes, and under the influence of various environmental factors, it can be increased, decreased, and even lost.

Endotoxins (internal toxins) are strongly associated with the microbial cell and are released into the environment only after the death of the microorganism. Endotoxins are usually produced by Gram-negative bacteria. By chemical nature it is a lipopolysaccharide complex that is part of the lipopolysaccharide complex of the cell wall. By character actions on the organism endotoxins do not differ in strict specificity and cause general signs of intoxication of the body: headache, fever, weakness, shortness of breath, vomiting, intestinal disorders. Endotoxins are resistant to high temperatures: they withstand prolonged boiling and even autoclaving for 30 minutes.

Exotoxins (external toxins) are released by microorganisms into the environment in the course of their vital activity. By chemical nature it's squirrels. They have a strict specificity of action on the body: they act only on certain cells and tissues (nerve cells, heart muscle, etc.). They are destroyed at 60-80 0 С within 10-60 minutes.

food infections

The occurrence of infectious diseases, their course and outcome depend not only on the amount of the pathogen entering the macroorganism and biological properties pathogenic microbe, but also to a decisive extent from the stability and resistance of the macroorganism to infection, i.e. on the state of his immunity.

Immunity- this is a protection system, i.e. a set of factors and mechanisms aimed at maintaining the genetic constancy of the internal environment of the macroorganism. From the point of view of infectious pathology, immunity is the immunity of the body to infection by pathogenic microorganisms.

Sources infections are sick and recovered people and animals that release pathogenic microbes into the environment. Exist two major way transmission excitationatparents infectious diseases: by direct contact with the source of infection and by indirect contact through intermediaries. The period from the moment of infection to the appearance of the first symptoms (signs) of the disease is called andncubation period.

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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, necessary for the body nutrients. 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 acid 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.

In most cases, koumiss is prepared in a handicraft way - in lime 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, reaches 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 oil from raw materials, equipment, 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 occurs: 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 of raw materials prevent defects in cheeses and make it possible to obtain a product 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?

Introduction

Microbiology of milk. Microbes get into the milk already at the time of milking. The origin of milk microflora is very diverse. Some microbes live in the teat canals of the udder and are therefore always present in the milk produced. In addition, a lot of microbes get into milk from the surface of the udder, animal hair, from the hands of milkers, from manured bedding, inventory, etc., microbes can be introduced into milk by flies. Due to these sources, the number of microbes in 1 ml after milking increases from several thousand to tens and hundreds of thousands after processing - filtering, cooling and spilling. As a result, a very rich microflora is formed. Rapid cooling is a mandatory operation, otherwise the development of microflora in uncooled milk occurs quickly. This is facilitated by the favorable chemical composition of milk. In uncooled milk, the number of microflora increases by 2-3 times in 24 hours. When cooled to 3-8 ° C, the opposite picture is observed - a decrease in the number of microorganisms occurring under the influence of bactericidal substances contained in freshly milked milk. The period of delay in the development of microbes or their death in milk (bactericidal phase) is the longer, the lower the temperature of the stored milk, the less microbes in it. This phase usually lasts from 2 to 40 hours.

In the future, there is a rapid development of all microbes. However, lactic acid bacteria, if they were previously even in the minority, gradually become predominant. This is explained by the fact that they use milk sugar, which is inaccessible to most other microorganisms, and also by the fact that lactic acid and the substances secreted by some of them - antibiotics (nisin) inhibit the development of all other microbes. Gradually, under the influence of accumulated lactic acid, the reproduction of lactic acid bacteria also stops. In milk that has undergone fermentation, conditions are created for the development of mold fungi.

The most actively developing are oidium, penicillium and various yeasts. By consuming acids, desalination of products, mold fungi create the possibility of secondary colonization of the object with putrefactive bacteria. Ultimately, complete putrefactive spoilage of milk occurs.

In pasteurized milk, briefly heated to 63-90 ° C, the sequence of changes in microflora changes dramatically. Almost all lactic acid bacteria die, and the bactericidal substances of milk are completely destroyed. At the same time, heat-resistant and spore forms of microorganisms are preserved. Therefore, after some time, rapid reproduction of the preserved diverse microflora can begin in such milk. The absence of bactericidal substances, the small number or complete absence of lactic acid bacteria make milk “defenseless”. Under these conditions, milk may not turn sour, but even a slight contamination with putrefactive or pathogenic bacteria leads to spoilage, making it dangerous for consumption. In this regard, it is clear why when trading pasteurized milk, it is necessary to strictly comply with sanitary and hygienic requirements and observe temperature storage conditions.

In recent years, a lot of sterilized milk has come into the market. During sterilization, microflora is completely destroyed and milk is given high storage stability. For the preparation of sterilized milk, low-contamination, absolutely fresh, pre-homogenized raw milk is used. A single sterilization is carried out at 140°C for several seconds. Therefore, in All biological properties are preserved in milk, even vitamins - C, B1, B6, B12 are little destroyed.

When using low-quality milk, spores of hay and potato bacilli, cereus bacilli, etc. can persist. They can cause spoilage of sterilized milk, decomposing proteins in it.

In addition to the normal microflora of milk discussed above, one should take into account the possibility of the formation of an unusual microflora in it, i.e., abnormal. It includes pathogens of various infections - typhoid fever, dysentery, brucellosis, etc., as well as microbes that cause the appearance in milk of a bitter, salty, soapy taste, blue or reddish color, etc.

Microbiology of dairy products. Condensed milk is a stable product. In the process of heating and sterilization of milk packaged in cans, most of the microorganisms in it die off. Only a few spores remain viable.

Microbiological spoilage most often occurs when using unsuitable, i.e., heavily contaminated with microbes, raw materials. The development of spore bacteria and less often thermophilic fungi leads to fermentation and putrefactive processes in condensed milk.

Less stringent requirements for contamination with microflora and acidity are imposed on raw milk used to produce sweetened condensed milk. The action of the second preservative factor, the high osmotic pressure created by sugar, prevents the germination and development of spores. Such milk is rarely subjected to microbiological spoilage.

Powdered milk has a more abundant microflora than condensed milk. This is due to the short duration of heating and the low temperature during drying. Milk powder preserves all types of spore microorganisms, heat-resistant non-spore species of micrococci, streptococci, some lactic acid bacteria, mold spores. This normal microflora can cause spoilage - souring, molding, etc. - only with significant moistening of milk powder.

The detection of non-heat-resistant forms in milk powder - Escherichia coli and pathogenic streptococci - may indicate the use of low-quality raw materials, non-compliance with the thermal processing regime, violation of sanitary standards during packaging and packaging.

Microbiology of sour-milk products. It is determined primarily by the composition of the used factory starter cultures, the microflora of the milk used and the sanitary and hygienic condition of the production equipment - milk containers, pipelines, etc.

For the preparation of sour-milk products, starters of a pure culture of one or another type or a mixture of pure cultures of several types of lactic acid bacteria are introduced into pasteurized chilled milk. For the production of kefir and koumiss, starters are used, which also contain yeast.

The use of pure cultures of various pathogens of lactic acid fermentation ensures the production of high quality finished products with certain stable properties. The admixture of random microflora degrades the quality of these products.

The microflora of cheeses is represented mainly by microorganisms that took part in the fermentation of milk and in the processes of maturation. The microflora that developed from the starter is only partially preserved, since a significant part of it dies during the long second heating of the cheese grain (up to 40-57 ° C). Up to 100 million cells are stored in 1 g of cheese grain. Subsequently, during pressing, their number increases several times. The formation of a crust on cheese, salting prevents the development of microflora on the surface. Further development of microbiological processes - lactic acid and propionic acid fermentation - occurs during the maturation of cheeses. These anaerobic processes develop inside and gradually capture the peripheral parts of the cheese. Depending on temperature, humidity, salinity, density of heads, amount of residual sugar and other factors, this or that process predominantly takes place, on which the specific consumer advantages of cheeses depend. By the end of maturation, the number of lactic acid bacteria decreases and the number of propionic acid bacteria increases. The weak proteolysis of proteins caused by them, the accumulation of various acids, the formation of eyes due to moderate carbon dioxide form the taste, aroma, texture and pattern of cheese dough.

In soft, slimy cheeses, unlike hard cheeses, the ripening process proceeds from the surface inwards. Various aerobic and conditionally anaerobic bacteria and mold fungi participate in maturation. The total number of bacteria in 1 g of cheese is billions of cells.

Some spore microorganisms, for example, butyric ones, can also be found in cheeses. Abundantly releasing carbon dioxide and hydrogen, they can cause the formation of an irregular pattern, swelling, cracking of cheese heads, and give them an unusual taste. When storing cheeses in conditions of high humidity, in places where the rind is damaged, they can be affected by mold fungi. Spoilage gradually develops in depth and is accompanied by softening of cheeses, the formation of a fluffy coating on the surface, and the appearance of an unpleasant odor.

1. Yeast found in the production of milk and dairy products. Their role in shaping the quality of dairy products

The main microflora of fermented milk products is lactic acid bacteria and yeast. Microorganisms are isolated in laboratories pure form and specially grown (cultivated). Such micro-organisms grown for specific purposes are called "cultures" (culture of lactic streptococcus).

Milk fermented by introducing certain cultures of lactic acid bacteria or yeast into it is called ferment and is intended for fermentation of milk in the production of fermented milk products. The following pure lactic acid cultures and yeasts are used for the preparation of starter cultures: lactic streptococcus (S. Lactis), Bulgarian bacillus (L. Bulgaricus), acidophilus bacillus (L. acidophilus), aroma-forming bacteria (S. diacetylactis, L. cremoris, S. acetoinicus, S. cremoris) and milk yeast (Torula) fermenting lactose, bifidobacteria and other probiotic cultures.

Lactic acid streptococci increase the acidity of milk up to 120 °T, lactic acid sticks (Bulgarian and acidophilus) - up to 200-300 °T and are the most powerful acid-forming agents.

For the preparation of industrial starters, starters of pure cultures of lactic acid bacteria are used, which can be liquid and dry. On liquid or dry sourdough, a primary (laboratory) sourdough is first prepared. To do this, a portion of liquid or dry starter is added to sterile milk, mixed and kept in thermostats at a temperature that is optimal for this type of culture.

A secondary (transplant) starter is prepared from the primary (laboratory) starter; for this, 5% of the primary starter is added to chilled milk and kept at the fermentation temperature. The secondary starter can be used as the main starter to obtain a production starter.

The acidity of the production starter on lactic acid streptococci should be 90-100 °T, on lactic acid sticks 100-110°T.

Before using the starter, its organoleptic characteristics are checked. A benign starter should quickly ferment milk, have a clean taste and smell.

The clot should be homogeneous, sufficiently dense, without gas formation and released serum.

Kefir fungi (grains), whose microflora is a symbiosis of lactic acid streptococci and rods, aroma-forming bacteria and lactic yeast, mycoderma and acetic acid bacteria, are used to prepare laboratory starter in the production of kefir.

The activity and purity of starter cultures largely determine the quality of the finished product.

With a decrease in the activity of starter cultures (the duration of clotting), milk does not ferment or a flabby clot forms. With the development of heat-resistant lactic acid sticks, excessive acidity of the product appears. Yeast involved in the maturation of kefir, koumiss, acidophilus-yeast milk, with excessive reproduction, causes swelling of these products. The ingress of acetic acid bacteria into sour cream, cottage cheese can cause texture defects.

Milk and most dairy products are a breeding ground for various microorganisms, both pathogenic and spoilage microorganisms.

Milk obtained from sick animals is dangerous to health, it can cause infectious diseases, staphylococcal toxicosis and other food poisoning.

Fresh milk obtained from healthy animals has bactericidal properties. The bactericidal phase lasts from several minutes to 45 minutes if the milk is at a temperature not higher than 0 ° C. Then the number of microorganisms begins to increase, and the faster, the higher the storage temperature of milk.

Raw milk can contain micrococci, streptococci, as well as Klebsiella, Yersinia, Proteus and Escherichia coli (coliforms), etc. If the storage and sale conditions are violated, microbes in milk and dairy products multiply rapidly, which leads to an unpleasant taste, changes in the properties of milk and his damage.

When lactic acid bacteria begin to predominate and acidity increases, the milk turns sour, the development of many other bacteria is suppressed. Then the lactic acid microflora gradually dies off, creating conditions for the growth of yeast, mold fungi, and then rotting microorganisms.

Pasteurization of milk is carried out in order to destroy pathogenic microorganisms and reduce the total contamination of milk. Milk is pasteurized at 76 ° C with a holding time of 15-20 s. After pasteurization of milk, a certain amount of thermophilic and heat-resistant bacteria (including enterococci) and spores remain. Such milk should be stored at a temperature of +4 °C for no more than 36 hours. Sterilized milk contains practically no microorganisms and can be stored for a long time.

Dairy products(sour cream, cottage cheese, kefir, curdled milk, etc.) have greater storage stability than milk. They are an unfavorable environment for the development of many pathogenic bacteria. This is due to the increased acidity of the products and the antibiotic properties of some starter cultures.

In the manufacture of fermented milk products, starters are used that contain pure cultures of lactic acid streptococci, Bulgarian and acidophilus bacilli, or mixtures thereof. For the production of kefir, the so-called kefir fungus is used - a symbiosis of yeast and other microorganisms.

Cheeses are obtained by fermenting milk with lactic acid bacteria, and then introducing rennet, which activates the coagulation of milk. Next, the process of maturation of the cheese takes place - under the action of the microbes of the starter, lactic acid and propionic acid fermentation occurs. As a result, milk sugar is fermented, proteins are partially broken down, and a specific taste and aroma appear. The carbon dioxide released during these processes forms cheese eyes.

In the production of some soft cheeses, cultures of mold fungi from the genus Penicillium are used.

Cheese spoilage is most often due to mold, the development of butyric acid bacteria leads to bloating, and some lactic streptococci to bitterness.

Ways of penetration of microbes into milk during manual and machine milking.

Milk is produced in the mammary gland of mammals. According to I. P. Pavlov, milk is “an amazing food prepared by nature itself.”

Milk serves as a good nutrient medium for the development and reproduction of all kinds of microorganisms, so one or another number of microbes can always be found in it.

The udder always contains bacteria that have passed here through the teat canal. There are more microorganisms in the nipple canal, in the milk tank and less in the excretory ducts and pier. alveoli.

Some of the microbes that have penetrated here die under the action of cidal substances, while the other part remains viable.

In milk obtained in compliance with all aseptic rules,

i.e. preventing external contamination, bacteria are still detected - from several tens to several hundreds in 1 ml.

If there is no proper udder care, then there can be much more microorganisms in the milk.

There are especially many microorganisms at the inlet of the nipple in contact with external environment. They accumulate here, form a cork. There may also be pathogenic species.

This prevents contamination of all milk and the environment.

A large number of microorganisms are present in milk with inflammation of the udder - Mastitis.

Microbes can penetrate into the udder from the outside through the teat canals and by the hematogenous route.

The microflora of the udder is usually divided into obligate and facultative.

Obligate Microorganisms have adapted to existence in milk and can always be found there. For example, coccal forms, which are practically harmless, because they cause slow changes in milk.

Facultative microbes get inside the udder and stay there temporarily. These include various cocci (micrococci, streptococci), close to intestinal lactic acid bacteria. They have the ability to liquefy gelatin and give milk a bitter taste.

With mastitis, in addition to cocci, E. coli and other microorganisms are found in milk.

The integument of the animal (skin, udder surface) contains a large amount of microorganisms that can enter the milk during milking.

The dirtier the skin of the animal, especially the udder, the more microorganisms enter the milk. for example, when wiping the udder with a dry towel, about 50 thousand microbes were found in 1 ml of milk, and only 3 thousand with a wet towel.

Microorganisms get to the surface of the skin from bedding, food, air, etc.

All this shows how important it is to keep the udder, body surface and barnyard clean.

Manure is one of the main sources of milk microorganisms.

Litter, especially if it is scattered shortly before milking or during milking, has a great influence on contamination and bacterial contamination of milk.

There are a lot of microbes in straw bedding, among which there are mold and bacteria that spoil milk. There are especially many microorganisms in old, rotten straw.

In this regard, the best litter material yavl. peat and fresh straw.

It has been established that in 1 g of straw litter there are on average 115 million microbes, and in 1 g of peat - about 27 million.

In addition, peat absorbs more water and gases. A number of microbes, for example, from the intestinal group, in peat litter, according to A.K. Skorokhodko, die within 6-8 days.

In some foreign countries (Germany) in cowsheds, the bedding is regularly sprinkled with superphosphate in order to eliminate the unpleasant smell of rotting bedding and to more quickly decompose the straw.

Feeds, especially dusty ones, are also a source of milk contamination if they are distributed during milking.

Microorganisms can get into milk from the air along with dust. Their content will depend on the number of microbes in the indoor air and barnyards.

Cleaning of premises should be carried out in a wet way, which dramatically reduces the number of microbes, and hence the possibility of getting into milk.

Hands of a milkmaid. A person can also inseminate milk with microbes if hygiene rules are not observed. On the surface of the skin of people, especially under the nails, there are a lot of microbes. Among them may be pathogenic microorganisms.

The milkmaid's hands should be clean, dry, nails cut short.

Therefore, before milking, it is necessary to thoroughly wash your hands with a brush and soap.

Milk utensils that are not washed enough can cause microbial contamination of the milk.

The purity of the water used to wash dishes also plays an important role in the bacterial contamination of milk.

In addition to saprophytes, water may also contain pathogenic microbes.

Therefore, water for washing milk dishes is periodically examined in the laboratory.

If a large number of microbes are found, the water is boiled or chlorinated before drinking.

Flies are a dangerous source of microbial contamination of milk, both during milking and subsequent storage of milk. Flies have thousands of microbes on their bodies.

Sitting on various garbage and feces, and then on milk utensils and milk, flies contaminate milk with various microbes, including pathogens.

Therefore, a systematic fight against flies in the barn is necessary: ​​thorough cleaning, washing, whitewashing, disinfection and disinfestation of both milk collection points and farms.

Bacterial contamination of milk with machine milking can be significantly less than with manual milking.

This requires thorough cleaning and disinfection of equipment - milking machines, filters and used utensils.

During machine milking, milk enters the closed system, which protects it from the ingress of microbes from the outside.

If the maintenance of milking equipment is careless, with poor organization of machine milking, many microbes remain on the walls of the tube and other parts of the machine, which leads to a deterioration in the sanitary quality of milk.

Careful processing of milking equipment with warm (50 ° C) water with the addition of 1% soda, the use of desmol and other des. substances followed by rinsing with warm water significantly reduces the bacteria content in milk.

Milk produced by a well-washed milking machine is stored longer. The work of milkmaids is facilitated and they need less. The possibility of infection of milk through hands is excluded.

The advantages of machine milking are obvious.

Straining milk

It aims to trap particles of dirt, manure, and with them microbes. However, a positive result will be achieved if straining is carried out immediately after milking, until the impurities have had time to dissolve in the milk.

centrifugation

It can also be used to purify milk. It is necessary to periodically clean the centrifuge (from mucus) and disinfect it after 1-1.5 hours.

Thus, the above data show how important it is to strictly observe zoohygienic and other sanitary rules in the dairy business.

Changes in the microflora of milk during storage.

The composition and number of microbes change during storage. These changes depend on the temperature and duration of storage, as well as on the composition of the microflora of the milked milk.

The dynamics of microbiological processes in milk from the moment it is received to its full use as a food product can be divided into several phases.

Bactericidal (cidal, antimicrobial or static) phase.

It is typical for freshly milked milk and chilled. In such milk, microbes not only do not multiply, but there is also a slight decrease in their number.

Such a delay in the development of bacteria and a decrease in their number occurs under the influence of several factors.

The antimicrobial properties of milk are due to Gamma - and beta - globalins, lysozyme, lacteins, bacteriolysins, antitoxins, agglutinins and other substances that come from the blood or are formed by the mammary gland.

It is noted that in the early period of lactation there are more antimicrobial substances in milk than at the end of lactation.

It is known, for example, that Lysozyme inhibits the growth of both saprophytes and pathogenic microbes.

The activity of antimicrobial substances depends on the degree of contamination of milk with bacteria, the speed of cooling, the temperature of cooling and storage.

When milk is heated, the activity of bactericidal substances increases, and at 56 ° C and above, they are inactivated.

Thus, the duration of the antimicrobial phase depends on two main factors: the degree of purity of the milk and the storage temperature.

The less bacteria in the milk, the faster it cools and the lower its cooling temperature, the longer the bactericidal phase.

For example, milk obtained under normal conditions at to 13-14 ° had a bactericidal phase of 19 hours, and obtained aseptically - 36 hours.

Or, according to R.V. Davidov, the antimicrobial phase of usually obtained milk was at 0o - 48 hours, at 5oC - 36 hours, at 10oC - 24 hours, at 25o - 6, at 30o - 3, and at 37oC - only 2 hours.

Thus, to prolong the antimicrobial phase, milk must be rapidly cooled.

The increase in the antimicrobial phase is of great practical importance, since it allows milk to be stored longer and delivered fresh to consumers.

In practice, two methods are used to extend this phase: elimination of sources of milk contamination and the second - immediate cooling of milk after milking.

Farms have special baths and installations for this.

After the end of the Antimicrobial phase, when the action of substances that inhibit the development of microorganisms has already ceased, the development of all microbes that have entered the milk begins.

This period is usually called the Phase of development of mixed microflora.

At the beginning of the phase, various groups of microorganisms develop - putrefactive, lactic acid, staphylococci, etc., but mainly ammonifiers. Along with this, there is an increase in the number of lactic acid bacteria. The duration of the phase is 12-18 hours.

At the beginning, lactic streptococci develop (Str. Lactis and others). Lactic acid accumulates in milk, which has a harmful effect on putrefactive microorganisms, which gradually die. As a result of low pH and the accumulation of microbial waste products, streptococci also die. The rod-shaped forms of lactic acid bacteria remain, i.e., at the end of this phase, some lactic acid bacteria are replaced by others. The lactic acid bacteria phase lasts 3-4 weeks.

Mushrooms and yeast use part of the lactic acid as food, and part is neutralized.

The acidity of milk gradually decreases, the pH rises and the environment becomes suitable for the development of putrefactive microflora and butyric acid bacteria.

Milk becomes completely unsuitable for nutrition.

The described change in the phases of the microflora is typical at t = 10°C and above, since lactic acid bacteria develop at +10° and above.

For a different t, the phase change may proceed differently. At tо from 5 to 10о, putrefactive, fluorescent microbes and micrococci develop.

Canned milk products - sweetened condensed milk, sugar-free condensed milk, milk powder, etc. - can be stored for a long time without a significant increase in the content of microbes in them.

Milk canned food is prepared by heat treatment, removing moisture from the product, drying and adding sugar. The usual constituents of milk are not destroyed.

Condensed milk is sterilized at TO 115-118оС – 15 min. Or to pasteurized milk condensed to 1/3 of the original volume Sugar is added (Not less than 43.5%).

When drying milk, a significant part of the microbes dies.

Sanitary and microbiological characteristics of milk.

For milk there is GOST. Milk and cream are produced by city piers. pasteurized plants, they should not contain germs.

Depending on the number of microbes and colitis, milk is divided into two groups A and B.

Gr. A - pasteurized milk in bottles and bags should contain no more than 75 thousand microbes in 1 ml and 1 E. coli per 3 ml of milk is allowed.

Gr. B - pasteurized milk in flasks and tanks - the total number of microorganisms in 1 ml is not more than 300 thousand, and the colititer is 0.3 ml.

Group A milk can be used for human consumption without boiling. Group B milk is boiled.