Lactic acid bacteria refer to Lactic acid bacteria (streptococci). General concepts about lactic acid bacteria

Taxonomy. Lactic acid bacteria belong to the department Firmicutes (Gram-positive eubacteria with a cell wall). They have two families: Lactobacillaceae And Streptococcaceae. Typical species of the genus Streptococcus is Streptococcus lactis, sort of Lactobacillus- Lactobacillus lactis.

Morphology and physiology. This is a morphologically heterogeneous group of bacteria - includes rod-shaped and spherical organisms. All lactic acid bacteria are gram-positive and do not form endospores (with the exception of Sporolactobacillus inulinus) and are overwhelmingly immobile.

These are facultative anaerobes. Carbohydrates are used as an energy source and form lactic acid. Lactic acid bacteria are only capable of fermentation; they do not respire. All lactic acid bacteria have complex requirements for growth factors: B vitamins, amino acids, as well as purines and pyrimidines. Consequently, lactic acid bacteria are a kind of “metabolic invalids” who, probably as a result of specialization (growth in milk and other media rich in nutrients and growth substances), have lost the ability to synthesize many metabolites.

A distinctive physiological feature of lactic acid bacteria is their high resistance to acid, which is a consequence of their characteristic energy metabolism. The ability of lactic acid bacteria to form and tolerate fairly high concentrations of lactic acid has important selective significance, since this property gives them the opportunity to successfully compete with most other bacteria in nutrient-rich environments.

Lactic acid bacteria can be divided into two physiological and biochemical subgroups, differing in the products that are formed from glucose as a result of fermentation:

1. Homofermentative lactic acid bacteria form almost only one lactic acid. These include bacteria species Streptococcus lactis, Streptococcus cremoris, Lactobacillus bulgaricus, Lactobacillus lactis and etc.

2. Heterofermentative lactic acid bacteria form a mixture

lactic acid, ethanol and CO2, and sometimes acetic acid. These include Leiconostoc mesenteroides, Lactobacillus brevis, Bifidobacterium bifidum and etc.

Distribution in nature The growth of lactic acid bacteria is determined by their complex nutrient requirements and the way they obtain energy. They are almost never found in soil or bodies of water. In natural conditions they are found:

In milk, dairy products, in milk processing areas ( Lactobacillus bulgaricus, Lactobacillus lactis and other lactobacilli; Streptococcus lactis);

On the surface of plants as epiphytic microflora and on decomposing plant debris ( Lactobacillus plantarum, Lactobacillus brevis, Leiconostoc mesenteroides);

In the intestines and on the mucous membranes of humans and animals as representatives of normal microflora ( Lactobacillus acidophilus, Bifidobacterium bifidum, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus faecalis, Streptococcus bovis and etc.).

Due to the fact that lactic acid bacteria are used for preparing food products and act as pathogens of human and animal diseases, they represent a group of great economic importance.

Lactic acid bacteria are used to prepare:

1) silo;

2) sauerkraut, cucumbers, etc. ( Leuconostos mesenteroides And Lactobacillus plantarum);

3) lactic acid products. Sterilized or pasteurized milk or cream is fermented by adding pure cultures of lactic acid bacteria as a starter. To prepare various lactic acid products, appropriate microbial starters are used.

For example, bacteria are used to make yogurt Streptococcus thermophilus And Lactobacillus bulgaricus; for making kefir - Lactococcus lactis, Lactobacillus kefir, Lactobacillus kefiranofaciens; sour cream – Lactococcus cremoris, Lactococcus lactis, Leuconostoc lactis And Leuconostoc mesenteroides subsp. cremoris;

4) raw smoked sausages. The lactic acid formed during fermentation gives a certain taste and also lowers the pH, which protects those types of sausages that are not cooked from spoilage;

5) sour dough when making bread. The resulting lactic acid is used to rise the dough and also gives the bread a specific sour taste;

6) obtaining pure lactic acid, which is used in the leather, textile, pharmaceutical, food industries and for the production of biodegradable materials (polylactides) used for food packaging.

Lactic acid bacteria can also play a negative role, causing spoilage of beer, fruit juices, meat and other products. This group also includes bacteria pathogenic for humans and animals, which are classified as streptococci.

Pathogenic properties of streptococci are caused by the formation of either exotoxins or the formation of heat-stable endotoxins. In addition, pathogenic streptococci produce virulence enzymes: hyaluronidase, deoxyribonuclease, ribonuclease, neuraminidase, proteinase, streptokinase, amylase, lipase, etc.

Exogenous and endogenous infection with streptococci is possible.

Exogenous infection with streptococci(from sick people, animals, infected products and objects) occurs through the outer skin and mucous membranes, as well as when streptococci penetrate into the intestines with food. The main route of infection with streptococci is airborne.

Endogenous infection opportunistic streptococci - inhabitants of the human body - is possible as a result of weakening of the body's immunity.

Streptococcal infections are divided into suppurative And non-suppurative . Suppurative diseases caused by streptococci include acute infections of the upper respiratory tract (in particular, pneumonia), erysipelas, or erysipelas, and sore throat. Upon penetration into the bloodstream, streptococci cause O a difficult septic process is poured in. The group of non-suppurative diseases includes scarlet fever, rheumatism, etc.

Pathogenic species include viridans streptococci Streptococcus pneumoniae. They often cause pneumonia, as well as sore throat, sinusitis, acute catarrh of the upper respiratory tract and other diseases.

Bacteria species Streptococcus viridans- permanent inhabitants of the oral cavity and pharynx of healthy people. They belong to viridans streptococci. They have weak virulence for humans and animals. They are found in purulent and inflammatory lesions of teeth and gums and cause subacute endocarditis.

Bacteria species Streptococcus pyogenes cause erysipelas, abscesses in wound infections. They belong to hemolytic streptococci.

3 Normal human microflora, its significance for the body

According to the journal Science ( science) for 2010, to date scientists have identified a set of bacteria and viruses that live in close symbiosis with humans, and in fact - we are like "Microbiome". As it turns out, 9 out of 10 cells in the human body are bacterial. According to various sources, the human microflora includes: 500 before 1000 different types(many of them are still unknown). Mostly they are friendly to the organism that is considered their “home”, and only a few lead to disease.

As part of normal microflora distinguish:

Permanent, or resident microflora - is represented by a relatively stable composition of microorganisms, usually found in certain places of the human body in people of a certain age;

Transient, or temporary microflora - enters the skin or mucous membranes from the environment, without causing diseases and not permanently living on the surfaces of the human body. It is represented by saprophytic opportunistic microorganisms that live on the skin or mucous membranes for several hours, days or weeks. The presence of transient microflora is determined not only by the supply of microorganisms from the environment, but also by the state of the host’s immune system and the composition of the permanent normal microflora.

Composition of transient microflora may vary depending on:

From age;

Environmental conditions;

Working conditions, diet;

Previous diseases;

Injuries and stressful situations.

The normal microflora of individual biotopes has the following basic properties:

1) it is quite stable;

2) is represented by several species, among which dominant species and filler species are distinguished;

3) each ecological niche has its own species composition. Some biotopes are stable in their composition, while others (transient microflora) are constantly changing depending on external factors;

4) microorganisms that make up the normal flora form a biofilm;

Biofilm represents a clear morphological structure - it is a polysaccharide framework consisting of microbial polysaccharides and mucin, which is produced by the cells of the macroorganism. In this framework, microcolonies of bacteria are immobilized - representatives of normal microflora, which can be located in several layers. The thickness of the biofilm ranges from 0.1 to 0.5 mm.

5) the normal microflora includes both anaerobic and aerobic bacteria; anaerobic bacteria predominate, the ratio of which in most biocenoses is 10: 1-100: 1.

6)!!! The colonization of various areas of the body by bacteria begins at the moment a person is born and continues throughout his life.

7) The formation of the qualitative and quantitative composition of normal microflora is regulated by complex antagonistic and synergistic relationships between its individual representatives within biocenoses.

Normally, many tissues and organs of a healthy person are free of microorganisms, i.e., sterile. These include:

Internal organs;

Brain and spinal cord;

Alveoli of the lungs;

Inner and middle ear;

Blood, lymph, cerebrospinal fluid;

Uterus, kidneys, ureters and urine in the bladder.

The sterility of organs and tissues is ensured by the presence of nonspecific cellular and humoral immunity factors that prevent the penetration of microbes into these tissues and organs.

On all open surfaces and in all open cavities, a fairly stable microflora is formed, specific to a given organ, biotope or its area - epitope. Richest in microorganisms.

Korzhova Ekaterina

The research work was prepared for the scientific and practical conference of the Nizhnevartovsk region "XXI century. In search of perfection." Took second place. Included in the collection of materials from the NPC students of the Nizhnevartovsk region

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Introduction

Bacteria are the oldest group of living organisms. Their study began three centuries ago. Lactic acid bacteria can rightfully be called the most common and often mentioned in ordinary everyday life. A person encounters them every day when he reaches out to the counter with lactic acid products in a store.

In the course of becoming familiar with the content of the work, someone will not want to buy this or that fermented milk product, and he will not regret it at all.

Perhaps many people do not want to buy a drug at the pharmacy to restore intestinal microflora after taking antibiotics, but will replace it with a glass of freshly prepared homemade kefir or yogurt.

An obese person will not run to get coded or buy diet pills, but will remember the old proven method - kefir after six.

Women will save money on cosmetics if they take into account information about the therapeutic effects of lactic acid bacteria on skin, hair and nails.

Target work: to reveal the role of lactic acid bacteria in human life.

Tasks the following were supplied:

Study of prokaryotes using lactic acid bacteria as an example.
A summary of material that serves as evidence of their use in the food, cosmetic and medical industries.
Study of the composition of lactic acid products.
Identification of “useful” and “harmful” lactic acid products for human health.
Mastering the technique of preparing lactic acid products (kefir and yogurt) at home.

Object of study selected lactic acid bacteria.

Subject of research - lactic acid products, obtained from these bacteria.

The work consists of two parts.

IN theoretical partIssues related to the history of discovery, forms, and types of bacteria are covered. Information about the most important fermented milk products and their widespread use in human life has been collected and processed.

IN practical partData are provided on the qualitative and quantitative composition of the most common and attractive lactic acid products. The results of the study formed the basis for producing healthy products at home: kefir and yogurt. Experiments have proven that these are real “live” products. Having made calculations, we came to the conclusion that receiving them at home is not only useful, but also profitable.

In the process of preparing the work, various sources of information were used. The most complete and interesting was obtained from biological and medical sites.

History of the discovery of bacteria (prokaryotes).

Bacteria - These are very ancient organisms that occupied all habitats. But they were discovered relatively recently, in the 17th century.
The first person to see microorganisms wasDutchman Antonio van Leeuwenhoek.Interested in the structure of flax fiber, he polished several rough lenses for himself. Placed them in silver frames. Thus, the first magnifying glass appeared. With the help of such a magnifying glass, Leeuwenhoek saw bacteria for the first time. Here is an excerpt from his letter to the Royal Society of London: “On April 24, 1676, I looked at the water... and with great surprise I saw in it a huge number of the smallest living creatures...”. This is how the science of microbiology was born.

The first one to see microflora fermented milk products, wasFrenchman Louis Pasteur. Examining sour milk under a microscope, Pasteur discovered very small “balls” and “sticks” in it. Observing them, Pasteur became convinced that the “balls and sticks” in sour milk were growing, and their number was rapidly increasing. “Therefore, they multiply,” Pasteur decided. By adding a tiny amount of sour milk containing “balls and sticks” to fresh milk, Pasteur caused it to sour, that is, lactic acid fermentation. These studies have generated great interest in this topic. Through the efforts of scientific microbiologists, both the physiology of the microorganisms themselves and the biochemical processes of fermentation and putrefaction caused by bacteria were studied. The normal inhabitants of even good milk are lactic acid bacteria and yeast. In warm milk, bacteria multiply very quickly: every half hour they can split in half and produce two new ones. Thus, within a short time, the number of bacteria in 1 mm of warm milk can reach several million, which will affect its quality - it will turn sour if lactic acid bacteria predominate in it, or acquire an unpleasant taste if unwanted bacteria, such as peptonizing bacteria, develop.

Shapes of bacteria

The forms of bacteria are quite diverse. Here is an incomplete list of known forms discovered by microbiologists using an electron microscope. (photos of bacterial forms, see appendix)

Types of bacteria.

Bacteria are classified according to different parameters.

By functions performed:

Rotting bacteria
Soil bacteria
Lactic acid bacteria
Acetic acid bacteria
Alcohol fermentation bacteria
Pathogenic (disease-causing) bacteria

By food type:

Heterotrophic
Autotrophic (chemosynthetics and photosynthetics)

In relation to oxygen:

Aerobic
Anaerobic

Lactic acid bacteria are representatives of prokaryotes.

Lactic acid bacteria, like all prokaryotes, do not have a nucleus. The carrier of hereditary information is a spiral strand of DNA localized in the cytoplasm. From the environment, the internal contents are limited by the membrane and a thin cytoplasmic membrane.

All lactic acid bacteria belong to two genera:

Genus Streptococcus species Streptococcus Lactisare oval-shaped cocci 0.8-1.2 microns that form chains of varying lengths. When aging, the chain fragments.
Species Streptococcus diacetilactis- these are smaller cocci, the diameter of which is 0.5-0.7 microns. They form chains of varying lengths, the waste products of which impart flavor to the product.
Genus Lactobacillus - are rod-shaped cells: 6-8 microns long, forming short chains. Non-spore-forming.

The most widespread:

Lactobacillus bulgaricum.
Lactobacillus acidophillum.

Fermented milk products and their importance in human life.

Fermented milk products are included in the diet of any person. Depending on the combination of genera and species of lactic acid bacteria, various fermented milk products are obtained from them. Milk is an amazing invention of nature. Man has long appreciated the nutritional and medicinal properties of milk and not only learned to use this product, but also significantly improved it. Various fermented milk products began to be produced from milk. For example: yogurt, kefir, yogurt, sour cream, cottage cheese, butter. Over time, many questions have arisen about the qualitative composition and effect of fermented milk products on the human body.

Brief information about the composition of fermented milk products

The product's name	Compound
Milk	With a pure cow, one milliliter of fresh milk contains about 100,000 bacteria , of which a share putrid accounts for approximately 96% and share lactic acid bacteria - 4%.In this regard, it is not advisable to drink fresh milk; accordingly, it is necessary to drink mature milk; it should sit for a day at a temperature of 8-10°C. During this time the attitude changesputrefactive and lactic acid microflora: 4% putrefactive and 96% lactic acid bacteria.
Kefir	Kefir grains are a complex symbiosis (coexistence) of microorganisms formed during a long process of development. Aged microorganisms behave like a whole organism. They grow together, reproduce and pass on their structure and properties to subsequent generations. White or slightly yellowish kefir grains have a specific sour taste. Their main microflora consists oflactic acid bacilli, streptococci and yeast.They determine the specific taste and aroma of kefir, its nutritional properties. During the life of the kefir grain, the microorganisms that make up its composition cause changes in the milk. Under the influence of lactic acid streptococci and rods, lactic fermentation occurs, yeast causes alcoholic fermentation. Thanks to these processes, the constituent elements of milk undergo changes, especially milk sugar. The resulting carbon dioxide and alcohol activate the activity of the stomach, accelerate the digestion process, and stimulate the appetite. Lactic acid has a beneficial effect on the intestinal microflora and delays the development of putrefactive bacteria.
Sour cream	To make sour cream you need cream. In this case, cleanbacterial cultures,which includelactic acid and creamy streptococci And aroma-producing bacteria.
Cottage cheese	Cottage cheese is fermentedpure cultures of lactic acid streptococci and aroma-producing bacteria. Sourdough usually has a sour milk taste, without any odors, gas formation, or protruding whey. Cottage cheese cannot withstand long-term storage, as lactic acid bacteria and molds multiply quickly in it.
Yogurt	In yogurt, a variety discovered by I. I. Mechnikov is used as a starter.lactic acid bacteria - Bulgarian bacillus. When making yogurt, the starter consists of pure culturesthermophilic streptococcus and bulgaric bacillus, contained in equal proportions. If this ratio is violated, the product may acquire a sharply sour taste, a grainy structure, or quickly release whey.

Medical scientists consider kefir and yogurt to be the most useful fermented milk products. They are widely used not only as valuable food products, but also as medical and cosmetic preparations.

The mysterious history of kefir and its medicinal properties.

There are many legends, rumors and mysteries associated with this product, which is quite familiar to our modern life. The origins of kefir grains are shrouded in mystery. Some associate its origin with the ancient peoples who inhabited Tibet and, accordingly, call it the Tibetan fungus. According to this version, the fungus occupied a place of honor among other mysteries of Tibetan medicine. It was brought to Europe from India by a certain Polish professor, who was cured of stomach and liver cancer with the help of kefir. According to others, the birthplace of the kefir grain is the mountain villages of North Ossetia, where the fermented milk product itself still plays an important role in the national cuisine. Muslims inhabiting the North Caucasus considered kefir grains to be a gift from the Prophet Muhammad himself and jealously guarded the secret of the production of the divine drink. In the mid-19th century, rumors about its amazing healing properties and wonderful taste reached Russia. How kefir fungus finally got into our country is unknown. There were rumors about the successful actions of the most famous detectives in the service of the government. No less popular was the story about the prince in love and the Russian girl Irina, who received the treasured recipe as a gift in honor of reconciliation after a quarrel with the prince.
Be that as it may, by 1907, the famous breeder Balandin, at the request of the All-Russian Society of Doctors, established the production of kefir in Russia. Following the example of Europe, kefir clinics began to appear and gain popularity in our country, where they admitted patients with rickets, anemia, dropsy, lung diseases, various gastrointestinal and gynecological diseases. It has been proven that the use of lactic acid productsaccelerates the removal of various radionuclides.A real fermented milk product necessarily contains live microorganisms (lactic acid bacteria), which make up the bulk of the microflora of the human digestive tract. An imbalance of microflora, called dysbiosis, can lead to all sorts of diseases: gastric and duodenal ulcers, allergies, gastritis. One of the most unpleasant consequences of dysbacteriosis is a decrease in the body’s immune functions; it entails protracted treatment of diseases and the development of complications. Due to impaired digestive functions, fatigue increases, fatigue and lethargy appear. Dysbacteriosis is common in both adults and children. The cause of their occurrence may be stress, unfavorable environmental conditions, poor-quality drinking water and food. The intestinal microflora is also disrupted after taking antibiotics, which kill bacteria necessary for the body.Treat dysbacteriosisit is necessary to take medications, but to prevent itFermented milk products help, first of all kefir and biokefir and bifidok prepared on its basis. These drinks, equivalent in composition, are improved kefir with the addition of bifidobacteria - microorganisms characteristic of humans that help the digestion process (they account for, for example, about 90% of the microflora of the large intestine). The Japanese use kefir for preventiontreatment of ancogynesis of the stomach and intestines. Lactic acid products “healthy” the intestinal microflora and treat gastritis. To treat gastritis with high acidity, fresh (one-day old) kefir (contains traces of alcohol) is used, and with low acidity - three-day old kefir. Alsolactic acid bacteriasuppress the development of putrefactive bacteria, which cause colitis: Shigella, which causes dysentery, and Salmanella, which causes typhoid fever.

Kefir has become widespread in cosmetology. Many balms, masks, shampoos, and creams are made on its basis. For example, a simple recipe for making a hair mask, useful in the spring, when hair becomes brittle and dry.

Lactic acid products create a fatty film that protects hair from damage by the alkaline solution formed when soap is dissolved in water. You need to take, say, yogurt or kefir, moisten your head generously, cover it with a plastic scarf, and top it with a terry towel. After 25-30 minutes, rinse your hair in the foam of toilet soap, such as “Children’s”, rinse thoroughly with just warm water, and then with acidified water (1 tablespoon of vinegar per 2 liters of water).

If you have problems with freckles, then a mask of fresh kefir can also come in handy. The brightness and number of freckles can be reduced if you wipe your face with fresh kefir every day.

The fungus between the toes can be removed by daily soaking a gauze cloth in a kefir solution and wrapping the feet at night. This procedure will not only help get rid of nail fungus, but also promote the growth and strengthening of nails, softening the skin on the feet.

Yogurt and its medicinal properties.

Yogurt is a European synonym for the Ossetian word “kefir”, a fermented milk product. It is made into yogurt by special bacteria - the so-calledBulgarian bacillus and Staphylococcus thermophilus. Fermented milk products obtained with the help of other microorganisms, accordingly, are not yoghurts. True “just yogurt” may not appeal to everyone. It tastes downright sour. However, this is the most natural product that promotes digestion. Natural yogurt is an effective means of restoring intestinal microflora. Yogurts are recommended for people who have been taking antibiotics for a long time, which destroy any bacteria. They, antibiotics, don’t care whether the bacteria are harmful or beneficial. Yogurt helps preserve beneficial microflora in the body, without which the intestines cannot function normally. Yogurt is used in the treatment of gastrointestinal diseases, colitis, cholecystitis, tuberculosis, furunculosis, childhood chest asthma and other diseases. Eating this product helps improve digestion and metabolism. For those who have had a little too much during the holiday feast, yogurt will help relieve hangovers and headaches. Yogurt is valuable not only as a food product. It is used to make perfumes that improve hair and skin. The West has long realized that yogurt is perhaps the healthiest fermented milk product, so Europeans consume it in huge quantities - from 13 to 35 kilograms per year per person.

What is “live” and “dead” yogurt?

When buying yogurt, you should remember that among them there are “live” and thermally processed ones. Only “live” yogurts bring benefits to the body, that is, prepared on the basis of milk using a special starter (a set of lactic acid bacteria of certain strains). It provides probiotic microflora, which is the enemy of microorganisms that cause various diseases and nutritional disorders. Thanks to lactic acid bacteria, “live” yogurt, like all fermented milk products of this kind (kefir, yogurt), stops putrefactive processes in the intestines and increases the body’s resistance to infections. Real “live” yogurt has a shelf life of no more than three weeks and should only be stored in the refrigerator. Often on the packaging of such a product there is a special marking indicating the content of live yogurt culture. Heat-treated yoghurts have a longer shelf life, and this is achieved through heat treatment of the product, during which the starter cultures are killed. In fact, these are no longer yoghurts, but yoghurt-based drinks. At first, the domestic market was flooded with just such imported products, which were called yoghurts, but in fact were not such. However, manufacturers’ statements that their yogurt is “more alive than all living things” do not guarantee that the product you purchased has beneficial properties. And first of all - because of the peculiarities of its transportation and storage. Yogurt is a very delicate product, and it is impossible to bring it from afar without a special refrigerator. “Live” yogurt that does not contain preservatives runs the risk of spoiling on a long journey. Once the temperature rises a few degrees, yogurt bacteria begin to multiply rapidly - and eventually suffocate from lack of oxygen. This yogurt reaches the buyer sour and “dead”. Therefore, “live” yoghurts taken from a store counter are often no longer real. Nowadays, the concept of “long-lived yogurt” is being actively promoted in the consumer environment. From what kind of “good intentions” of the food industry such long-lived yoghurts are born does not need much explanation. It is important to remember something else: the content of active microorganisms cannot remain at the level that provides a preventive and health-improving effect for a long time. If the packaging has a one-month expiration date, it means it is “long-lived” yogurt. That is, there is no beneficial microflora in it.

What is yogurt made from?

Currently they produce three types of yoghurts:

Yogurt as such (i.e. without fruit or flavor additives),

Fruit or vegetable yogurt

Flavored yogurt.

Just yogurt, as already said, is a pure white milk drinkwithout any additives, it is as healthy as possible compared to other types of yogurt.

In fruit or vegetable yogurt, up to30% flavoring additives.When you buy yogurt, for example, with pear flavor, you get a lactic acid product that, of course, never contained any pear. Actually, pear essence is butyl acetates (butyl esters of acetic acid). Yogurt manufacturers claim that these esters are absolutely harmless. However, you need to know that butyl acetate is a solvent that is used in the production of paints and varnishes.

Flavored yogurt differs from plain yogurt in that it contains:various flavors- natural or identical to natural. By purchasing yogurt, for example, with apricot flavor, you get the same healthy lactic acid product with food additives that are approved and safe for use.

Yogurts with fruit fillings - pieces or whole berries - are best avoided altogether, unless, of course, the word “health” has any meaning to you. The fact is that these “pieces” are sterilized without heat treatment. They protect fruits and vegetables from spoilage in a very original way, namely by irradiating them with a “peaceful atom”. The irradiation process is simple - pallets of food are placed in a special chamber, where a grid with cobalt-60 (a radioactive isotope of cobalt) rises from the water and bombards fruits and vegetables with radiation. Manufacturers assure that if everything is done according to the rules, products after irradiation do not become radioactive, but become sterile. But we can say more precisely - they become nothing. Irradiation breaks down vitamins and enzymes, that is, it makes the product “dead.” In addition, radiation breaks down the molecular structure of fruits and vegetables, resulting in a range of chemicals called “unique radiolytic products.” These include benzene, formaldehyde and many other mutagens and carcinogens. A sort of cocktail with berry and fruit pieces floating in a yogurt mixture. Of course, the content of harmful substances in fruit and berry yogurt is negligible, but their very presence makes this drink “empty” at best.

Medicinal properties of yogurt.

The bacterium Helicobacter pylori is considered importantcause of peptic ulcer,Therefore, antibiotics are used to treat it. However, in 10-23% of patients, antibiotics do not work. Scientists from Taiwan proposed in this case the use of yogurt containing bifidobacteria and lactobacilli.
They have proven that consuming this yogurt before repeating a combination treatment significantly improves results. Scientists examined 138 patients whose Helicobacter pylori infection could not be cured after using a three-component treatment regimen. Before the course of four-component therapy, some patients consumed yogurt, others did not. After a second course, 91% of patients who consumed yogurt and only 77% of those who did not consume this product completely got rid of H. pylori. “The bacteria contained in yogurt act on H. pylori and reduce its content in the body,” the scientists comment on their work.

Brown University\\Brown Medical School announced the development of technology that can stop the spread of HIV\\AIDS through sexual contact. The technology is based on bacteria used in the production of yoghurts and cheeses.
The essence of the new technology is as follows: the protein cinovirine was previously discovered, which has the unique ability to block the access of the HIV\\AIDS virus to the body's cells. Using genetic engineering methods, cinovirine was combined with lactic acid bacteria, used to ferment milk and produce various dairy products. The resulting bacteria containing cinovirine can be used to make creams that can prevent infection with the “plague of the 20th century.” For example, they may be used before sexual intercourse. According to the World Health Organization\\World Health Organization, the AIDS epidemic has claimed the lives of more than 25 million people (3.1 million in 2005).

Practical part.

Composition of lactic acid products.

While searching for information about lactic acid bacteria and products obtained as a result of their activity, the idea arose of studying the composition of lactic acid products that are common on the shelves of our stores and, not so long ago, were included in the diet of schoolchildren. The results of the study are presented in Table No. 1.

Table No. 1

Composition of lactic acid products.

	Fats g per 100g	Proteins g per 100g	Carbohydrates g per 100g	Nutritional value Kcal	Lactic bacteria CFU	Yeast	Bifidobacteria	Best before date
Kefir								14 days
Bio-yogurt “Bio-balance”								21 day
Sour cream
Yogurt “Uslada” Vegetable-milk product, yoghurt, pasteurized			17,4		Skim milk, plant extracts, colors: E120, blueberry flavors, acidity regulators: citric acid, Na citrate, thickeners: guar gum, E412, glucose syrup, cream, gelatin, modified starch E1422, whey powder, sugar, water	4 months
Yogurt “Ermigut” Dairy-vegetable product, yoghurt, pasteurized, fruit			16,5		Skim milk, plant extracts, colors: E120, strawberry, pineapple flavors, acidity regulators: citric acid, Na citrate, thickeners: guar gum, E412, glucose syrup, cream, gelatin, modified starch E1422, whey powder, sugar, water	4 months
Miracle curd Curd product, thermized, whipped fruit flavored					Normalized milk, sugar, water, stabilizers: modified starch, gelatin, guar gum, locust bean gum, flavorings: vanilla, pear, coloring: annoto, citric acid, Na citrate, starter culture, rennet	1.5 months
Milk				62		6 months

Conclusion: The most valuable are kefir, drinking yogurt and sour cream, because they contain cultures of lactic acid bacteria and bifidobacteria. Eating “Miracle Curd”, “Uslada”, “Ermigurt” can be harmful to health, because they contain a large number of preservatives, thickeners, and flavorings. They are especially dangerous to use for allergic people.

Methods for making kefir and yogurt at home.

The topic of this work arose after I learned that using Tupperware you can make yogurt and kefir at home.

Therefore, the theoretical information collected on the issue of “lactic acid bacteria and lactic acid products” helped me conduct this useful research and gain experience, which I shared with friends and relatives.

The objects of the study were the following products:

Drinking yogurt "Prostokvashino" (1.5%)
Kefir "Doctor Brand" (2.5%)
Pasteurized fruit milk-vegetable yoghurt product “Ermigurt” (4.7%)

Description of the experience.

A starter of the lactic acid product under study is placed in 1 tablespoon cups. Added 200 ml of warm boiled milk.

Sugar was added to some samples to see if it would have an effect on souring the milk and how it would affect the consistency of the resulting product. The contents in the cups were placed in a Tupperware bowl and poured with boiling water, so that the cups were almost completely placed in hot water. The bowl was covered with a lid and left overnight.

For the convenience of describing observations, I suggest using

product consistency scale:

5 - very viscous, thick, similar to the original product

4 - viscous

3 - runny

2 - liquid

1 - very liquid, similar to milk

Viscosity scale

The results of the study were entered into table No. 2

Table No. 2

Samples	Drinking yogurt "Prostokvashino"	Kefir "Doctor Brand"	Pasteurized fruit milk-vegetable yoghurt product “Ermigurt”
sugarless	thick (5), not sweet, pleasant to the taste.	liquidish homogeneous mass (2)	very liquid (1), separated from milk, the mass is thicker at the bottom, milk at the top
with sugar	thick (4), sweetish, very tasty, sugar settles at the bottom in the form of sugar syrup.	not viscous (3) consistency, has lumps, sweet taste
double concentration, Sugarless	thick (5), not sweet, tasty	not viscous (3), more lumps, not sweet

Observational results show that the most active microorganisms are in drinking yogurt “Prostokvashino”. The resulting consistency is homogeneous and pleasant to use. Repeated use of the resulting starter in subsequent portions also gave positive results. The resulting yogurt -2 was even thicker than the first.

In the resulting kefir, lumps arise as a result of the fact that the kefir starter is formed by kefir grains, which are a complex symbiosis of lactic acid bacteria and yeast.

The difference in the consistency of the products is also explained by the fact that the content of lactic acid microorganisms and bifidobacteria (together) in drinking yogurt is 10 13 . and in kefir, lactic acid microorganisms and yeast (together) - 10 11 . (see “Composition of lactic acid products” table No. 1)

Nothing happened in the dairy-vegetable yogurt pasteurized fruit product Ermigurt. The reason for this is that he is "dead". All living microorganisms were destroyed during production, otherwise the shelf life of this product would not have been six months.

The shelf life of homemade yogurt and kefir is 1-2 days in the refrigerator.

Saving

Milk cost

Cost of sourdough

Total cost of product received

For 1 person

For a family of 4 people

For 1 person

For a family of 4 people

For 1 person

For a family of 4 people

1. Drinking yogurt

7 rubles

2 rubles

9 rubles

28 rubles

112 rubles

9 rubles

36 rubles

19 rubles

76 rubles

2. Kefir

7 rubles

0.8 rubles

8 rubles

9.25 rubles

37 rubles

8 rubles

32 rubles

1.25 rubles

5 rubles

Conclusion.

In the process of writing this work, I had to study a lot of literature and visit different sites. Some of them were purely advertising in nature, others actually highlighted the role of lactic acid bacteria and products in human life. There were also many critical articles regarding the use or non-use of lactic acid products both in the food industry and in medicine and cosmetology. When reading the literature, we must remember that bacteria are actually an ancient group of organisms, which, on the one hand, has been sufficiently studied, on the other hand, can present many secrets and mysteries.

Bacteria are living organisms that adapt well to life in any conditions. Maybe the time will come and people will use bacteria not only in the production of lactic acid products, wine, cosmetics, medicines, necessary genes, but also in the exploration of space, the bowels of the earth, and the treatment of modern technology. Maybe with the help of bacteria a person will defeat cancer and AIDS. It will be possible to subjugate pathogenic bacteria and direct their destructive power to peaceful purposes.

In my work, I considered only one type of bacteria - lactic acid bacteria. Despite the contradictory information received from different sources, I am convinced that these organisms, like little soldiers, do great things for humans. Therefore, I advise all my relatives and friends

1. Drink more kefir, it will help your intestines and skin.

2. Stop looking at the beautiful colored labels of “Miracle” products, there is nothing tasty or healthy in them.

3. Consider my experience in making homemade kefir and yogurt as it will save you money.

Glossary of terms

Prokaryotes - nuclear-free organisms.

Microbiology - a branch of biology that studies microorganisms.

Bacteriology - a branch of microbiology that studies bacteria.

Heterotrophic organisms- organisms that feed on ready-made organic substances.

Autotrophic organisms- organisms that produce organic substances from inorganic substances using light energy ( photosynthetics) or energy of chemical reactions ( chemosynthetics).

Aerobes - organisms that exist only in an oxygen environment.

Anaerobes - organisms that exist in an oxygen-free environment.

Microflora - living organisms, inside a product, an organ of the body.

Bibliography:

Dmitriev Yu.D. Entertaining biology: M.: Bustard, 1996 - 240s
Dronova O.N. Reader on biology: Bacteria. Mushrooms. Plants: Saratov: Lyceum, 2003 - 144 p.
Zakharov V.B. Sonin N.I. Biology 7th grade. Tutorial for

educational institutions. M.: Bustard., 2002

Zverev I.D. A book for reading on human anatomy, physiology, hygiene. A manual for students. M.: Education., 1971 - 315 p.
Nikishov A.A. Student’s Guide to Biology, grades 6-9: M.: Bustard., 1996 -176 p.
Kolesov D.V. Invisible “friends” of a person. // Biology at school.-

No. 3., 2003

Yakovlev G.P. Botany for teachers. Part 1. M.: Education., 1997-215s

Websites:

http://www. School - collection.edu.ru
http:// www.ecobios.ru
http://www. bidliotekar.ru
http://www. it-n.ru
http://www.setilab.ru

Spirilla - bacteria with an elongated spur-like convoluted shape

Staphylococcus - cluster of cocci in the form of a bunch of grapes.

Sarcin - spherical bacteria that look like dense packs.

Diplococcus - spherical bacteria linked in pairs.

Vibrios - arched, curved bacteria.

rods (bacillus) - solitary, straight-shaped bacteria.

Cocci - spherical single bacteria

Streptococci - spherical bacteria linked in a chain in the form of beads.

FORMS OF BACTERIA

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Ministry of Education and Science of the Russian Federation

Federal State Budgetary Educational Institution of Higher Professional Education "Moscow State Engineering University (MAMI)" (University of Mechanical Engineering)

ABOUT RESEARCH WORK

Lactic acid bacteria

Head Department Doctor of Technical Sciences, Professor Biryukov V.V.

Project leader teacher

department E&P. Samokhvalova N.S.

Moscow 2015

Introduction

2. Materials and methods

Conclusion

List of used literature

Introduction

Lactic acid bacteria are interesting microorganisms that interest scientists because of their functions and characteristics. Studying the presence of lactic acid bacteria in food products was one of the main tasks set for students in this research work.

1. Analytical literature review

1.1 Types of bacteria, their morphology and characteristics

Lactic acid bacteria are represented by rods of various shapes: from short coccoid-shaped to long filamentous. The length of cells in different cultures of the same species depends on the composition of the medium, the presence of oxygen, and the method of incubation.

Most lactic acid bacteria are probiotic strains isolated from the intestinal flora of a healthy person (bifidobacteria and lactobacilli), which remain viable when passing through the gastrointestinal tract and have a beneficial effect on human health, which is confirmed by clinical trials. They are included in medications, food additives, and, more recently, in fermented milk products.

Lactic acid bacteria reproduce by dividing by a septum, which leads to the formation of chains. The ultrafine structure of the cells of these bacteria is in many ways similar to other gram-positive bacteria.

On agar media, lactic acid bacteria form small ones. Lactic acid bacteria are demanding when it comes to food sources; they grow on media containing plant decoctions, meat and yeast extracts, and protein hydrolysates, since these bacteria need amino acids, vitamins and a number of inorganic compounds.

In nature, lactic acid bacteria are found on the surface of plants, in milk, external and internal epithelial integuments of humans, animals, birds, and fish.

The genus Streptococcus (species Streptococcus Lactis) are oval-shaped cocci 0.8-1.2 microns that form chains of varying lengths. When aging, the chain fragments.

The genus Streptococcus diacetilactis are smaller cocci, the diameter of which is 0.5-0.7 microns. They form chains of varying lengths, the waste products of which impart flavor to the product.

The genus Lactobacillus is a rod-shaped cell: 6-8 microns long, forming short chains. The most famous representatives of this genus are the species Lactobacillus bulgaricus and Lactobacillus acidophilus

Lactobacillus bulgaricus - Bulgarian bacillus. The bacterium is named so because it was once isolated from Bulgarian sour milk. A non-sporeless, non-motile bacterium, reaching 20 m in length and often connected in short chains. It is thermophilic and grows best at temperatures above 40°C.

Lactobacillus acidophilus is a species of gram-positive anaerobic non-spore-forming bacteria.

Lactobacillus leichmannii - this species is also included in the subgroup of thermobacteria. Bacterial cells are smaller, about 4 microns long and 0.6-1 microns wide, arranged singly or in chains. The presence of two or more grains of volutin in the cells is typical.

Lactobacillus plantarum ferments many sugars, including maltose and sucrose. For its development, it requires rich environments containing a variety of carbohydrates, vitamins, and amino acids. The optimal temperature for its development is 30°C, but it can grow within a fairly wide temperature range (15-38°C). It is alcohol-resistant, withstanding alcohol concentrations of up to 20% vol. The species L. plantarum is constantly found in sourdoughs and plays a major role in the process of acid accumulation.

Lactobacillus casei - this species also belongs to the subgroup of streptobacteria and is homofermentative in the nature of fermentation. According to morphological, cultural and physiological characteristics, it is very close to L. plantarum, and therefore difficult to distinguish from it. The significant difference is the ability of L. plantarum to grow in a medium containing 0.4% spool.

Lactobacillus brevis - the species belongs to the subgroup of beta bacteria. Ferments glucose to form carbon dioxide. The cells are predominantly short (2/4X0.7/1 µm) without inclusions of volutin grains, arranged singly or in chains of different lengths. Colonies are small, convex, whitish, shiny. The optimal growth temperature is 30°C, but can grow at lower temperatures (15°C).

Lactobacillus fermenti - this species is also heterofermentative. It has cells in the form of short rods (2/3X X0.5/1 µm), located singly or in chains. In terms of cultural and physiological properties, it is quite close to other species of the beta-bacteria subgroup. A distinctive feature of this species is that it does not grow on media containing 0.4% tipula and its temperature optimum for growth is much higher - in the range of 37-40°C. At 15°C no growth is observed. The species L. fermenti is often found in sourdoughs and appears to be specific to bakery production.

Lactobacillus buchneri - the species belongs to heterofermentative bacteria. The cells are very small - 0.74-4X0.35 microns, arranged singly, in pairs, often in long chains. Colonies are small, convex, opaque, yellowish. Grows in a wide temperature range - from 15 to 45°C. It differs from the species L. fermenti in its ability to grow in the presence of tipula, and from the species L. brevis in its ability to ferment melecytosis. The species L. buchneri is described in sourdoughs, but occurs in them in small quantities. [Kvasnikov V.I., Nesterenko O.A. Lactic acid bacteria and ways of their use, “Science”, 1975, pp. 1--384. ]

The first researcher to suggest that some bacteria are not at all harmful to humans, but on the contrary, can have a positive effect on health, was the famous Russian scientist Ilya Ilyich Mechnikov. At the very beginning of the 20th century. he conducted research on the possibility of restoring intestinal microflora using lactic acid coli. As a result of serious and painstaking research, the scientist studied the properties of the bacterium, which he called the “Bulgarian bacillus” (in the modern classification - Lactobacillus bulgaricus), and also developed a recipe for a fermented milk drink - the prototype of modern yogurt. I.I. Mechnikov himself, his colleagues and acquaintances for many years regularly consumed this drink, which is also called “Mechnikov’s curdled milk,” and were able to verify its beneficial qualities from their own experience.

Currently, a variety of positive effects of lactic acid probiotic bacteria are known, confirmed by numerous clinical studies.

Fermented milk products are included in the diet of any person. Depending on the combination of genera and species of lactic acid bacteria, various fermented milk products are obtained from them. Over time, many questions have arisen about the qualitative composition and effect of fermented milk products on the human body. (Table 1). Qualitative composition of lactic acid products in accordance with GOST

	Their main microflora consists of lactic acid bacilli, streptococci and yeast. They determine the specific taste and aroma of kefir, its nutritional properties. During the life of the kefir grain, the microorganisms that make up its composition cause changes in the milk. Under the influence of lactic acid streptococci and rods, lactic fermentation occurs, yeast causes alcoholic fermentation. Thanks to these processes, the constituent elements of milk undergo changes, especially milk sugar.
	To make sour cream you need cream. In this case, pure bacterial cultures are used, which include lactic acid and creamy streptococci and aroma-forming bacteria.
	Cottage cheese is fermented with pure cultures of lactic acid streptococci and flavor-producing bacteria. Sourdough usually has a sour milk taste, without any odors, gas formation, or protruding whey. Cottage cheese cannot withstand long-term storage, as lactic acid bacteria and molds multiply quickly in it.
	In yogurt, a variety of lactic acid bacteria, Bulgarian bacillus, discovered by I.I. Mechnikov, is used as a starter. When preparing yogurt, the starter consists of pure cultures of thermophilic streptococcus and Bulgarian bacillus, contained in equal proportions.

1.2 Technology for the production of lactic acid products

The production of dairy products in the food industry is based on fermentation processes. The basis of dairy biotechnology is milk. Milk (the secretion of the mammary glands) is a unique natural nutrient medium. It contains 82-88% water and 12-18% dry matter. The composition of milk solids includes proteins (3.0-3.2%), fats (3.3-6.0%), carbohydrates (milk sugar lactose - 4.7%), salts (0.9-1% ), minor components (0.01%): enzymes, immunoglobulins, lysozyme, etc. Milk fats are very diverse in their composition. The main proteins of milk are albumin and casein. Thanks to this composition, milk is an excellent substrate for the development of microorganisms. Streptococci and lactic acid bacteria usually take part in the fermentation of milk. By using reactions that accompany the main process of fermentation of lactose, other milk processing products are obtained: sour cream, yogurt, cheese, etc. The properties of the final product depend on the nature and intensity of fermentation reactions. Those reactions that accompany the formation of lactic acid usually determine the special properties of products. For example, secondary fermentation reactions that occur during the ripening of cheeses determine the taste of their individual varieties. Peptides, amino acids and fatty acids found in milk take part in such reactions.

All technological processes for the production of milk products are divided into two parts: 1) primary processing - destruction of by-product microflora; 2) recycling. Primary milk processing includes several stages. First, the milk is cleared of mechanical impurities and cooled to slow down the development of natural microflora. The milk is then separated (in the production of cream) or homogenized. After this, the milk is pasteurized, the temperature rises to 80°C, and it is pumped into tanks or fermenters. Recycling of milk can proceed in two ways: using microorganisms and using enzymes. Using microorganisms, kefir, sour cream, cottage cheese, curdled milk, casein, cheeses, biofructolact, biolact are produced; using enzymes, food hydrolyzate of casein, powdered milk mixture for cocktails, etc. When microorganisms are introduced into milk, lactose is hydrolyzed to glucose and galactose, glucose is converted into lactic acid, the acidity of the milk increases, and at pH 4-6 casein coagulates.

Lactic acid fermentation of glucose is the main process in the production of sourdough, cheese and fermented milk products, and lactic acid bacteria are the most important group of microorganisms for the dairy industry.

Lactic acid fermentation is the process of anaerobic oxidation of carbohydrates, the end product of which is lactic acid. It got its name from its characteristic product - lactic acid. For lactic acid bacteria it is the main route of carbohydrate catabolism and the main source of energy in the form of ATP. Also, lactic acid fermentation occurs in animal tissues in the absence of oxygen under heavy loads.

A distinction is made between homofermentative and heterofermentative lactic acid fermentation, depending on the products released in addition to lactic acid and their percentage. The difference also lies in the different ways of obtaining pyruvate during the degradation of carbohydrates by homo- and heterofermentative lactic acid bacteria.

In homofermentative lactic acid fermentation, the carbohydrate is first oxidized to pyruvate via the glycolytic pathway, then pyruvate is reduced to lactic acid NADH + H (formed at the stage of glycolysis during the dehydrogenation of glyceraldehyde-3-phosphate) using lactate dehydrogenase. The stereospecificity of lactate dehydrogenase and the presence of lactate racemase determine which enantiomer of lactic acid will prevail in the products - L-, D-lactic acid or DL-racemate. The product of homofermentative lactic acid fermentation is lactic acid, which makes up at least 90% of all fermentation products. Examples of homofermentative lactic acid bacteria: Lactobacillus casei, L. acidophilus, Streptococcus lactis12. Homofermentative fermentation products: curdled milk, yoghurts, acidophilus products, sour cream, cottage cheese and curd products.

For milk fermentation processes, pure cultures of microorganisms called starter cultures are used. The exception is kefir starters, which represent a natural symbiosis of several types of lactic acid fungi and lactic acid bacteria. This symbiosis could not be reproduced in the laboratory, so a culture isolated from natural sources is maintained. When selecting cultures for starter cultures, adhere to the following requirements:

The composition of starter cultures depends on the final product (for example, acidophilus is used to produce acidophilus, and lactic acid streptococci are used to produce curdled milk);

Strains must meet certain taste requirements;

Products must have the appropriate consistency, from brittle, grainy to viscous, creamy;

Certain acid-forming activity;

Phage resistance of strains (resistance to bacteriophages);

The ability for syneresis (the ability of a clot to release moisture);

Formation of aromatic substances;

Combinability of strains (without antagonism between cultures);

Presence of antibiotic properties, i.e. bacteriostatic effect against pathogenic microorganisms;

Drying resistance.

Cultures for starter cultures are isolated from natural sources, after which directed mutagenesis and selection of strains that meet the above requirements are carried out.

Safety when sowing m/o into fermented milk products

The greatest potential epidemiological danger is posed by the production of fermented milk products. This is due to the fact that the process of producing fermented milk products takes a long time, during which favorable opportunities arise for the proliferation of microorganisms remaining after pasteurization, as well as those that entered the milk as a result of secondary contamination.

After introducing the starter, the proliferation of most microorganisms is suppressed. However, under conditions of a slow increase in acidity as a result of reduced activity of the starter, they can actively multiply; in particular, the bacteriophage develops intensively. Microbes also develop intensively if milk is contaminated with small doses of antibiotics or other inhibitory substances.

Fermented milk products are not subjected to additional heat treatment. Therefore, all operations for the production of fermented milk products must be subject to increased sanitary, hygienic and anti-epidemic requirements.

To obtain epidemiologically safe fermented milk products, the following is necessary: use only pasteurized raw materials for the production of fermented milk products; normalization and homogenization should be carried out before pasteurization: pasteurization of milk should be carried out under more stringent regimes than established by technological instructions; add the starter immediately after filling the container or during the filling process; do not allow milk to remain at ripening temperature without fermentation; strictly control the quantity and quality of the introduced starter, the duration of ripening; reduce the production of fermented milk products using the thermostatic method as much as possible (completely switch to the tank method).

To develop fermented milk products with guaranteed sanitary quality, strict adherence to hygienic rules and technological regimes is required at all areas of production.

Fermented milk products are mainly produced according to a general technological scheme - fermentation of pasteurized (or sterilized) milk with sourdough. The production of individual products differs, as a rule, in the temperature conditions of some operations, the addition of fillers and the use of starter cultures of various compositions.

Fermented milk products are produced by thermostatic and tank methods. With the thermostatic method, ripening, cooling and maturation are carried out in bottles in thermostatic and refrigeration chambers. With a tank type, these processes occur in one container. After mixing the curd in the tank, the actual finished product is poured into the container, which must be further cooled. The reservoir method eliminates additional contamination of products, which is especially important in anti-epidemic terms.

For the production of fermented milk products, increased hygienic requirements are imposed on milk. The incoming milk is subjected to purification and normalization, after which it is sent for heat treatment. It is strictly forbidden to carry out normalization after pasteurization in order to avoid secondary contamination of milk.

Heat treatment is carried out under more stringent conditions than in the production of drinking milk. Pasteurization of the mixture is carried out at high temperatures (87±2°C, 92±2°C) with appropriate holding time (10-15, 2-8 minutes). For Ukrainian curdled milk, Varents and some other fermented milk products, an even higher heat treatment of the mixture is required: 97±2°C with holding time for 60±20 minutes. Such heat treatment not only completely destroys pathogenic microbes, but also reduces the amount of other microflora that can affect the activity of the starter.

The bacterial purity of milk is especially important, since during fermentation optimal temperature conditions are created for the development of the remaining microflora, which leads to a deterioration in the sanitary parameters of the product and can cause the release of products that are epidemiologically unsafe.

The pasteurization process is controlled in the same way as in the production of drinking milk. After cooling to the fermentation temperature, the milk is sent to tanks and the starter is added to them. [Kalinina L.V., Ganina V.I., Dunchenko N.I. Technology of whole milk products, St. Petersburg: Giord, 2008]

A serious danger in the production of lactic acid bacteria starter culture are phages, which are found for all streptococci and many types of lactic acid bacilli. If it is not necessary to isolate the bacterial mass after cultivation, then whole or skim milk can be used as the main milk. In the latter case, the yield of lactic acid bacteria is 1.0-10 4-2.0-10 cells per 1 ml of medium.

Relationships between microorganisms can also take different forms; an example of a symbiotic relationship can often be observed. Thus, kefir starters contain yeast and lactic acid bacteria. Bacteria produce lactic acid, which creates an acidic environment favorable for yeast, and the yeast enriches it with vitamins needed by lactic acid. Sometimes one group of microbes uses the waste products of another group, for example, during the biological treatment of pulp and paper wastewater, cellulose bacteria decompose the fiber of small wood fibers and form sugars and organic acids, and after them, other groups of microorganisms, using these substances as food, oxidize them to carbon dioxide gas and water.

Typical lactic acid fermentation is widely used for the production of lactic acid products in dairies. Lactic acid bacteria are of great importance in the preservation of fresh feed by silage - Preservation of succulent feed mass is based on the fermentation of sugars contained in plant juice with the formation of lactic acid. Thanks to the environment, the development of putrefactive processes in the silage mass is prevented. Recently, silage starters from lactic acid bacteria have been developed. The use of these starters allows you to speed up and improve the process of silage maturation and avoid the formation of butyric acid.

Liquid starters are a semi-finished product in which, upon production, mesophilic heterofermentative lactic acid bacteria and yeasts that got there spontaneously (for example, with flour) or were introduced on purpose . When using liquid starters in the dough, not only alcoholic fermentation occurs, but also active lactic acid fermentation, while the pH of the dough decreases to 4.7-4.8.

A good nutrient medium for propagating a culture of lactic acid bacteria intended for drying is sterile skim milk with a high content of solids (up to 16%), which is achieved by adding milk powder and 0.1% sodium citrate. The seed material should be 1% of the volume of the medium. The process of bacterial reproduction is carried out without aeration at a temperature of 30°C for 12-16 hours for lactic acid streptococci and at 40°C for 6 hours for lactic acid rods. Then the culture medium is neutralized with a 20% sodium hydroxide solution to the original acidity of sterile milk. [Ignatiev V.E. Kefir // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional ones). -- St. Petersburg, 1890--1907.]

Fermentation and fermentation of milk are the most vulnerable stages of the technological process for the production of fermented milk products in hygienic and epidemiological terms. Therefore, careful adherence to fermentation and ripening regimes should be given special importance. The most dangerous cases are those when conditions are created for potentially pathogenic or pathogenic microflora that have survived after pasteurization or have entered the pasteurized mixture to facilitate its reproduction.

In order to promptly identify the causes of existing violations, it is necessary to constantly note in production logs the time of filling containers and fermentation, the duration of fermentation, the activity of the starter, etc.

The use of starter cultures prepared using the direct-transfer method is of great importance, and it is necessary to use only fresh starter culture, made no later than a day before its consumption, preferably with sterilized milk. This is due to the fact that sterilization (or high-temperature pasteurization) completely destroys the microflora of milk, which may include heat-resistant microorganisms

To obtain a hygienically high-quality product, the starter should be immediately added to the cooled mixture after pasteurization, and in the future the progress of the lactic acid process should be strictly monitored.

The quality of the starter is checked daily, determining activity, the presence of foreign microflora by viewing a microscopic specimen in 10 fields of view of a microscope, the quality of the clot, taste and smell.

After fermentation, the process of fermentation of milk begins. With the thermostatic method, the fermented mixture is first poured into bottles (jars), sealed, labeled and placed in thermostatic chambers. The duration of fermentation depends on the type of product being produced and ranges from 3 to 10 hours at a temperature of 35-42°C, depending on what type of starter is used and what fermented milk product is produced.

Increasing the fermentation temperature is undesirable, as this leads to more intensive development of coliform bacteria. The end of ripening is determined by the formation of a sufficiently dense clot and acidity, which is 70-80°C for Varenets, 75-85°C for yogurt, 65-70°C for fermented baked milk. With the tank method, the ripening process is carried out in tanks. They also cool the finished product.

At the end of fermentation, the fermented milk products are gradually cooled in the refrigerator to a temperature not exceeding 6±2°C; during this period the product should acquire a dense, uniform consistency. A number of fermented milk products, after cooling (kefir, kumys), are kept for a certain time in refrigeration chambers for maturation. Upon completion of ripening, the products are transferred for storage and sale. The air temperature in storage rooms before sale should be no higher than 6-8°C. Shelf life is no more than 18 hours. Compliance with the rules of cooling and storage is the most important hygienic requirement.

Finished products are monitored for the presence of coliform bacteria and microscopic samples from one or two batches at least once every 5 days. Microbiological indicators of the finished product must be no lower than 0.3 ml in terms of coli titer.

Equipment that comes into direct contact with the product during the production process requires special attention. Before starting the technological process, such equipment should be thoroughly sanitized. If the sanitary indicators of the finished product deteriorate, a thorough analysis and additional monitoring of the technological process is carried out to establish the causes of secondary contamination of the product, the quality of the starter is checked, as well as the sanitary and hygienic condition of the workshop.

Today, yogurt is bought one and a half times more often than kefir. Fruit additives, a varied palette of flavors and convenient packaging play an important role here. To obtain a truly high-quality product - yogurt of the required consistency, viscosity, taste, smell, appearance, and also free from syneresis - many factors must be taken into account during the production process. Decisive are the selection and preparation of raw materials (that is, the milk itself), the preparation of the starter, and most importantly, correctly designed and optimally configured production lines.

Only the highest quality milk is used to make yoghurt. This means that it must contain a minimum amount of bacteria and foreign impurities that will inhibit the development of the culture, such as antibiotics, bacteriophages, as well as residues of the washing solution.

The milk processing process includes several main technological stages, each of which is equally important to achieve high quality of the final product. The basis for this is laid already at the stage of milk processing.

First, milk is normalized for solids content (DSC). Increasing the total solids content, especially the ratio of casein to other whey proteins, results in a thicker yoghurt: thus reducing the tendency for whey to separate. Typical methods of standardization for TER are evaporation (10-20% of the total milk volume is usually evaporated), addition of skim milk powder (usually up to 3% w/v), and addition of concentrated milk. Typically, milk for making yogurt is normalized to a fat content of 0.1 to 3.5%, and the lower the percentage of fat in the milk, the more sensitive the yogurt curd is to processing. Taking this into account, TIR is increased more often in the production of low-fat yogurt than in whole yogurt. The air content in milk should be minimal. However, the presence of air in small quantities is still inevitable, especially if the TCO is increased by adding milk powder early in the process. To remove the air contained in the original milk, the raw material enters vacuum chambers for deaeration. Deaeration increases the stability and viscosity of yogurt; removes extraneous volatile odors and reduces fermentation time. In addition, the process improves the performance of the homogenizer and reduces the risk of burning during cooking.

The next stage in the preparation of yoghurt raw materials is homogenization. Its main purpose is to prevent cream from settling during ripening and ensure uniform distribution of fat in the milk. Homogenization also affects the stability and consistency of fermented milk products, even those with low fat content. To obtain a product of optimal quality, it is recommended to homogenize milk at a pressure of 200-250 atm. and temperature 65--70°C.

Next, the milk is subjected to heat treatment before the starter is added to it. This is done to improve the properties of milk as a base for bacterial fermentation, and also ensures the formation of a curd in the finished yogurt and reduces the risk of whey separation in the final product. The most optimal heat treatment mode is achieved at a temperature of 90-95°C and a holding time of about 5 minutes. This mode makes it possible to denature most of the proteins, providing them (and therefore the curd) with the ability to bind water. The result is yogurt with a more stable consistency. To achieve the best effect, the product must be kept at the required temperature in the holding tube.[Yogurts. General technical conditions GOST R 51331-99]

An equally important technological stage in the preparation of yogurt is the choice of starter and its preparation. Strict hygiene plays a decisive role here: the preparation of the starter should be carried out in a separate, specially equipped room to reduce the risk of contamination.

Yogurt starters typically consist of two types of bacteria: Lactobacillus bulgaricus and Streptococcus thermophilus. However, other types of bacteria are sometimes added to the main starter, for example, Lactobacillus acidophilus and Bifidobacterium. Both types of bacteria grow interconnected and produce lactic acid as the end product of airless milk fermentation. Streptococcus thermophilus is mainly responsible for acid production, while Lactobacillus bulgaricus gives yogurt its distinctive flavor. The interaction between the two types of bacteria is influenced by the amount of each type added, as well as the temperature and time of ripening. [Kvasnikov V.I., Nesterenko O.A. Lactic acid bacteria and ways of their use, “Science”, 1975, pp. 1-384.]

If we talk about methods of propagating working starter, then in recent years concentrated forms have been mainly used - both for propagating working starter and for direct introduction into the product. However, many dairies are increasingly propagating working starter cultures from mother cultures. At various stages of propagation, crops are named as follows:

Basic sourdough - it is purchased in laboratories for growing sourdoughs;

Royal - prepared from the main starter directly at the dairy;

Transplant - uterine culture in large quantities;

Working starter is a culture used to produce yogurt.

Since the curd obtained as a result of fermentation is quite sensitive to mechanical stress, the design of the installation plays a decisive role. When producing tank-type yoghurt, it is very important that the pressure difference between the incubation tanks and the packaging machine is minimal. Therefore, the correct selection of the type and size of pipes, valves, pumps, cooler, etc. is of paramount importance.

Cottage cheese is a valuable dietary product, indispensable in the diet of children and adults; it is not only rich in vitamins, but is also easily digestible. The proteins that make up cottage cheese contain essential amino acids and can serve as a substitute for other animal proteins for people for whom such proteins are contraindicated. Cottage cheese promotes the formation of hemoglobin in the blood and normalizes the functioning of the nervous system, is recommended for the prevention of metabolic diseases, and strengthens bone and cartilage tissue.

Cottage cheese is a fermented milk concentrated protein product with a protein mass fraction of up to 15-20%. Cottage cheese has a pure fermented milk taste and smell without any foreign shades. The consistency is delicate and homogeneous, for fatty cottage cheese it is slightly spreadable, for low-fat cottage cheese it is allowed to be heterogeneous, crumbly with a slight release of whey. The color is white, slightly yellowish with a creamy tint, uniform throughout the mass. According to microbiological indicators, the content of Escherichia coli bacteria in 0.00001 g of product and pathogenic microorganisms, including salmonella in 25 g of product, is not allowed in cottage cheese. Dairy industry enterprises produce the following types of cottage cheese:

Fatty - 18% fat content and acidity 200--225 T;

Bold -- 9% fat and acidity 210--240 °T;

Low-fat - acidity 220--270 T

Peasant - 5% fat content and acidity 200 “T;

Table - 2% fat content and acidity 220 °T;

Dietary -- 4% and 11% fat, low-fat, acidity 210--220°T;

Dietary fruit and berry -- 11.9.4% fat content, low-fat, acidity 180-- 200 T;

With fruits - 4% fat content, low-fat, acidity 200°T and other types of cottage cheese.

The technology for producing cottage cheese is based on fermenting milk with starter to obtain a curd and its further processing. The curd is obtained by acid and acid-rennet coagulation of milk proteins. With acid coagulation, fermentation prepared from pure cultures of lactic acid streptococci is added to milk during fermentation. Acid-rennet coagulation involves the addition of starter, calcium chloride and rennet. With acid coagulation, the clot is formed as a result of lactic fermentation and has a good consistency. However, when milk is fermented to produce fatty cottage cheese, the resulting curd does not release whey well. Therefore, in practice, the method of milk protein coagulation is chosen depending on the quality of the raw materials, the type of cottage cheese produced, available equipment, consumer orders, etc.

Cottage cheese production using the traditional method

The technological process consists of the following operations: reception and preparation, milk separation, normalization, pasteurization, cooling, fermentation and ripening of normalized milk, curd cutting, whey separation and curd bottling, self-pressing and pressing of curd, cooling, packaging, packaging, storage and transportation of cottage cheese .

Dairy raw materials intended for the production of cottage cheese are cleaned in milk separators or filtered through three layers of gauze or other filter fabric. Purified milk is heated to 37 ± 2 °C and separated in cream separators. When making full-fat, semi-fat and peasant cottage cheese, milk is normalized for fat, taking into account the mass fraction of protein in whole milk, to obtain a finished product with a given fat and moisture content. Skim or normalized milk is pasteurized at a temperature of 78 ± 2 ° C with a holding time of 15-20 s in plate or tubular pasteurization-cooling units or capacitive devices. After pasteurization, the milk is cooled to fermentation temperature. If milk after pasteurization is not used immediately for processing, then it is cooled to 6 ± 2 ° C and stored for no more than 6 hours. After storage, the milk is again heated to the fermentation temperature. The starter is prepared using pure cultures of mesophilic lactic acid streptococci. For accelerated fermentation, a starter prepared with pure cultures of mesophilic and thermophilic streptococci is used. The temperature of milk during fermentation is 30 ± 2 ° C in the cold season and 28 ± 2 ° C in the warm season, with the accelerated method - 32 ± 2 ° C, when using Darnitskaya starter culture - 26 ± 2 and Kaunasskaya starter culture -- 24 ± 2 °C. Before adding to milk, the surface layer of the starter is carefully removed with a clean, disinfected ladle and removed. Then the starter is mixed to a homogeneous consistency with a clean whorl (when prepared in starter tubs) or a stirrer and poured into the prepared milk in an amount of 1-5% of the total mass. During accelerated fermentation, 2.5% of the starter prepared on cultures of mesophilic streptococci, and 2.5% of the starter prepared on cultures of thermophilic streptococci is added to the milk. The duration of milk fermentation is 10 hours, and with the accelerated method - 6 hours. An aqueous solution of calcium chloride (mass fraction of calcium chloride 30-40%) is added to the milk after fermentation: 400 g per 1000 kg of fermented milk. It is necessary to restore the salt balance disturbed during pasteurization of milk. The preparation and preparation of calcium chloride solution is carried out in accordance with the Instructions for technical and chemical control at dairy industry enterprises. After adding the salt solution to the fermented milk, add a 1% enzyme solution at the rate of 1 g of the drug with an activity of 100,000 IU per 1000 kg of milk. Rennet, food grade beef or pork pepsin, or the enzyme preparation VNIIMS are used. When the activity of enzyme preparations is below 100,000 IU, their number is increased.

Rennet powder or pepsin is added to milk in the form of a 1% aqueous solution prepared in water boiled and cooled to 36 ± 3°C. To prepare a pepsin solution, it is recommended to use acidic whey, pasteurized and freed from proteins, at a temperature of 36 ± 3 ° C 5-8 hours before use. The enzyme solution is added to the milk with constant stirring. 10--15 minutes after adding the enzyme solution, finish mixing and leave the milk alone until a dense curd forms with an acidity of 61 ± 5 ° T for cottage cheese of 9% and 18% fat content, 65 ± 5 ° T for peasant and 71 ± 5°T for low-fat cottage cheese. The clot is checked for fracture and by the type of whey. If, when broken with a spoon or a removable ladle, a smooth edge with shiny smooth surfaces is formed, then the curd is ready for further processing. The serum released at the site of rupture of the clot should be transparent and greenish in color.

To process the curd, hand lyres are used, in which stretched thin stainless wire serves as knives. Using such wire knives, the curd is cut into cubes measuring 2x2x2 cm. The clot is first cut along the length of the bath into horizontal layers, and then along the length and width into vertical layers. After this treatment, the curd is left for 40-60 minutes to separate the whey and increase acidity. The separated whey is drained from the bath. After draining the whey, the curd is poured into calico or lavsan bags measuring 40x80 cm. The bags are filled to approximately 70%, which is 7 - 9 kg of cottage cheese. Then the bags are tied and placed one on top of the other in a self-pressing bath, press trolley or UPT installation for pressing and cooling the curd.

To speed up the separation of whey, as well as in case of poor whey separation, the curd is heated by supplying steam or hot water to the interwall space of the curd bath. To ensure uniform heating, the upper layers of the curd are moved with a wooden or metal plate (shovel) from one wall of the bath to the other. The curd is heated to 40 ± 2 "C for 30-40 minutes for cottage cheese of 9% and 18% fat content, 35 ± 2 "C for 20-40 minutes for peasant cottage cheese and 36 ± 2 "C for 15-20 minutes for low-fat cottage cheese. When using Darnitskaya sourdough, the curds with whey are heated to 34 ± 2 °C for 15-40 minutes.

Self-pressing of the cottage cheese continues for at least 1 hour. When using the UPT installation, the duration of pressing, depending on the quality of the resulting curd and the coolant (brine, ice water), is 1 - 4 hours. Pressing is continued until curd is obtained with the mass fraction of moisture specified in the regulatory documentation. For cottage cheese with 18% fat content it is 65%; 9% fat content - 73; peasant - 74.5; dining room - 76; low-fat - 80; for dietary fruit and berry 11% fat content - 64, 9% fat content - 66, 4% fat content - 77 and low-fat - 79% moisture. When producing low-fat cottage cheese, dehydration of the curd can be carried out using a curd separator. After separation and pressing, the curd is cooled using various equipment. The packaged cottage cheese is cooled to 6 ± 2 C, and the product is considered ready for sale

Features of cottage cheese production by other methods

Moldavian way. The main feature of this method is that the curd is cooled using cold whey taken from other batches by contact. Despite the faster production cycle, it is used extremely rarely due to the rough and rubbery consistency of the finished product.

Continuous method. Normalized milk is fermented with acid whey or lactic acid. The entire process from the formation of a clot to the receipt of the finished product is carried out in the interscrew chambers of one large cylinder. The consistency of the finished product is flabby, has high acidity, and during production there is a large loss of protein with whey. All this makes the production of cottage cheese using this method low-profit. On line Ya9 - OPT. This is the only method where milk is homogenized. Calle (curd with whey) is fed into a dehydrator, where after certain manipulations the finished product is formed. The quality of cottage cheese produced using this method corresponds to the quality of traditional cottage cheese.

Separate method. During the separation process, milk is divided into skim milk and cream with an MJ of 50 - 55%. Then the usual manipulations are carried out with skim milk. The resulting mixture is sent to a curd separator, where the curd is separated from the whey. The finished low-fat cottage cheese is mixed with cream to the required fat content. Soft dietary cottage cheese, as well as cottage cheese with fruit fillings, are produced using a separate method.

Membrane method. Used in the production of children's curds. The essence of the process is that before fermentation, milk is pre-condensed in an ultra-filtration unit. The fermented substrate is poured into consumer containers, where the final formation of the product occurs. The consistency of the cottage cheese is soufflé-like.

Kefir is the national drink of the peoples of North Ossetia. It has been known in Russia and other countries of the world for more than a hundred years. The uniqueness of this product lies in the use of a special starter prepared with kefir grains or specially selected pure cultures of microorganisms. Kefir is produced low-fat and with a mass fraction of fat 1; 2.5; 3.2 and 6%, dry matter 7.8; 8.1; 9.5 and 11%, as well as fruit, fortified and others with various original names. It is produced by reservoir and thermostatic methods. Kefir is a homogeneous liquid creamy product with a pure, specific fermented milk taste, milky white or slightly creamy in color. Kefir is characterized by certain organoleptic properties. The consistency is homogeneous and without sediment with a disturbed clot in the tank production method and with an undisturbed clot in the thermostatic production method. For low-fat kefir, as well as one percent, gas formation in the form of individual eyes is allowed. A slight separation of whey is allowed on the surface of kefir (no more than 2% of the volume of the product). The color is milky white, slightly creamy.

Kefir is produced from pasteurized milk by fermenting fungi with starter culture. Sourdough starters are prepared from kefir grains. To do this, one part of dry fungi is placed in 40-50 parts of warm (19°C in summer and 21°C in winter) skim milk. It is pasteurized at 92-95°C for 20-30 minutes. Kefir grains poured with milk are kept at 19-21°C until a clot forms for 20-24 hours. During this time, the milk and fungi are mixed 1-2 times. When a curd has formed, the fungi are separated and placed in warm (19-21°C) pasteurized milk. For one part of fungi take 30-50 parts of milk. Next, the fungi are cultivated as described above; usually 2-3 transplants are enough to revive the microflora of kefir grains. Lively fungi float to the surface of the milk and are used to produce fungal (working) starter. For this purpose, the revived fungi are placed in pasteurized chilled milk (19-21°C), one part is taken for 30-50 parts of milk; At the fermentation temperature, the milk is kept for 15-18 hours, after which it is thoroughly mixed and left for another 5-7 hours. After this, mix the contents again and then filter through a sieve. The resulting fungal starter is used to ferment milk to produce kefir, and the fungi are used to produce a new batch of starter. The starter culture includes lactic acid streptococcus, lactic acid bacillus, yeast and acetic acid bacteria.

To prepare a production (working) starter, you can also use a fungal starter. It is prepared as follows. 1-3% fungal starter is added to pasteurized and cooled milk (20-22°C); The fermentation process lasts 10-12 hours. In order to improve the taste and smell, the starter is kept for 5-6 hours at 20-22°C. It is better to use both kefir and fungal starter without refrigeration. If necessary, the starter is cooled to 3-10°C and stored for no more than 24 hours.

With the thermostatic method of producing kefir, 3-5% industrial or 1-3% fungal starter is added to chilled milk, mixed for 15 minutes, and then poured into bottles or bags with continuous stirring, sealed and kept in a thermostat for 8-12 hours at 18-21° With summer and 22-25C in winter. The end of ripening is determined by the consistency of the curd: it should be dense, without gas bubbles and an acidity of 75-80T. Bottles with finished kefir are cooled in the refrigerator, where it matures for 8-13 hours. Ready kefir has an acidity of no more than 36 hours from the end of its production. (1)

For the tank method of producing kefir, it is fermented in tanks at 23-25°C. After adding the starter (the same amount as with the thermostatic method), the mixture is stirred for 15 minutes, then left alone for 8-12 hours. at 23-25C. The finished curd has an acidity of 85-100T. At the end of ripening, the milk clot is stirred for 10-30 minutes (to obtain a homogeneous consistency) and cooled to 20+-2°C, and then left alone to ripen for 6 hours, then cooled to 6°C, stirred for 2-5 minutes. and bottled or packaged. The acidity of the finished kefir is 85-120T.

When producing fortified kefir, vitamin C is added to the starter 30-40 minutes before adding it to the milk. Next, the starter is stirred for 10--15 minutes and kept for 20--30 minutes. Vitamin C is added taking into account its content in the finished product, which is 110 g per 1000 kg of milk. The fermented milk is stirred. The duration of the first mixing is from 15 to 40 minutes, depending on the strength of the curd and the design of the mixer in the tank. When a homogeneous consistency is obtained, stop the mixer for 30-40 minutes, and then turn it on periodically for 5-15 minutes every hour. In kefir with a heterogeneous, lumpy consistency, whey may separate during storage. After cooling and stirring, the kefir is left alone to mature, which lasts at least 24 hours from the moment the milk is fermented. After ripening, the kefir is stirred again for 2-5 minutes and poured. After bottling, kefir is stored for 24 hours at a temperature not exceeding 8 °C.

So, fermented milk products have high nutritional value. They contain proteins, fats, calcium, phosphorus, provitamin A - carotene and vitamin B2. Fermented milk products are also of great value from the point of view of nutritional physiology, since lactic acid bacteria, in addition to fermentation, also cause weak protein breakdown. Thus, the human body is offered already partially processed, easily digestible protein; the proportion of free amino acids increases. Thanks to splitting and new synthesis, a rearrangement of vitamins occurs, which is well suited to human needs. Lactic acid arising from lactose promotes intestinal motility and calcium absorption; There is an increase in metabolism. Many people who do not tolerate regular milk well can take fermented fermented milk drinks without any harm.

The value of fermented milk products also lies in the fact that they contain microorganisms and their metabolic products, which inhibit putrefactive bacteria in the human gastrointestinal tract. This is also facilitated by lactic acid, which reduces the pH of the environment and also prevents the activity of putrefactive microorganisms. At least some of the microorganisms used (for example, Lactobacillus acidophilus, Bifidobacterium) have an antibiotic effect, so products made with their participation can be successfully used for certain digestive disorders. Fermented milk products have a beneficial effect on the nervous system and respiratory tract, stimulate appetite, have a pleasant, refreshing taste, and are used in the treatment of anemia, tuberculosis, and diseases of the gastrointestinal tract.

2. Materials and methods

lactic acid bacterium product probiotic

During the research, samples of fermented milk products were taken, such as kefir, sourdough, cottage cheese and fermented baked milk. Dilutions of lactic acid products and a suspension of cottage cheese were prepared. The stated number of CFUs was printed on the product packaging. On kefir it was written that the amount of Lactobacillus rhamnosus was 1x CFU/g, on sourdough 1x CFU/g, on fermented baked milk 1x CFU/g, on cottage cheese 1x CFU/g.

Various types of utensils and equipment were prepared for the work. To make it possible to dilute the specified amount, sterile test tubes, 1 ml pipettes, and 50 ml of sterile saline solution were prepared. MPA and MRS media were prepared for inoculation. Dilutions of kefir were prepared by introducing 1 ml of the product into 9 ml of saline solution, thus 7 dilutions were successively prepared, 5, 6 and 7 dilutions were placed on Petri dishes on both media. Dilutions of fermented baked milk were prepared, and 5, 6 and 7 were also planted on Petri dishes for both types of media. A suspension of cottage cheese was also prepared by adding 1 g of the product to 9 ml of water, stirring this solution until relatively homogeneous and further preparing 7 dilutions as described above. Dilutions 4, 5 and 6 were placed on Petri dishes on the above media. The starter was also diluted; dilutions 8, 9 and 10 were planted on nutrient media in Petri dishes. During the research, positive results were obtained only in experiments with kefir; colonies of lactic acid bacteria Lactobacillus rhamnosus, and 2 types of colonies of rods and cocci grew on the cup. During sowing of curds on MPA medium, a colony of mold grew. During sowing of the sourdough and fermented baked milk, negative results were obtained, the cups were empty.

...

1 General characteristics of lactic acid bacteria

and their features, types of fermentation

Lactic acid bacteria belong to the families Lactobacillaceae And Streptococcaceae. The distribution of lactic acid bacteria in nature is determined by their complex nutrient requirements and method of obtaining energy. They are almost never found in soil or bodies of water. In natural conditions they are found:

in milk, dairy products, in milk processing areas ( Lactobacillusbulgaricus, Lactobacillus lactis and other lactobacilli; Streptococcus lactis);

on the surface of plants as epiphytic microflora and on decomposing plant debris ( Lactobacillus plantarum, Lactobacillus brevis, LeAndconostoc mesenteroides);

in the intestines and on the mucous membranes of humans and animals as representatives of normal microflora ( Lactobacillus acidophilus, Bifidobacterium bifidum, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus faecalis, Streptococcus bovis(viridans streptococcus) and etc.).

Due to the fact that lactic acid bacteria are used for preparing food products and act as pathogens of human and animal diseases, they represent a group of great economic importance.

Cell morphology. This is a morphologically heterogeneous group of bacteria; it includes rod-shaped and spherical organisms, ranging in length from 0.7–1.1 to 3.0–8.0 μm, located singly or collected in chains. All lactic acid bacteria are gram-positive and do not form endospores (with the exception of Sporolactobacillus inulinus), capsules, and are overwhelmingly immobile. The shape and length of cells in different cultures of the same species of lactic acid bacteria often depends on the composition of the medium, the presence of oxygen and the method of cultivation.

Physiological and biochemical properties. These are facultative anaerobes that use carbohydrates as an energy source and produce lactic acid as the main fermentation product (for this reason they are combined into a separate large group of microorganisms). All lactic acid bacteria complex needs for growth factors are discovered : B vitamins, amino acids, purines and pyrimidines. Distinctive physiological feature of lactic acid bacteria – their high resistance to lactic acid, which is a consequence of their characteristic energy metabolism. The ability of lactic acid bacteria to form and tolerate fairly high concentrations of lactic acid has important selective significance, since this property gives them the opportunity to successfully compete with most other bacteria in nutrient-rich environments.

Lactic acid bacteria are usually only capable of fermentation.

Lactic acid fermentation call the anaerobic decomposition of carbohydrates by lactic acid bacteria with the formation of lactic acid and other products. Depending on which lactic acid bacteria cause this fermentation and what products are formed, it is of two types - typical, or homofermentative, And atypical, or heterofermentative .

Chemistry of homofermentative lactic acid fermentation simple It consists in the smooth splitting of hexose into two molecules of lactic acid, without the formation of gaseous products, according to the following summary equation:

C 6 H 12 O 6 = 2CH 3 -CHON-COOH + 18 kcal.

The intermediate products in this fermentation are pyruvic acid and hydrogen. By adding hydrogen, pyruvic acid forms lactic acid.

Chemistry of atypical lactic acid fermentation more complex, since here, during the fermentation of carbohydrates, along with lactic acid, heterofermentative bacteria form a number of other compounds: acetic and succinic acids, ethyl alcohol, carbon dioxide and hydrogen. The complication of the fermentation process is due to the fact that these bacteria contain the enzyme carboxylase in their cells, while homofermentative bacteria do not have it. The general chemistry of this process can be represented by a schematic equation like this:

2C 6 H 12 O 6 = CH 2 CHON-COOH + COOH-CH 2 -CH 2 COOH +

CH 3 COOH + CH 3 CH 2 OH + CO 2 + H 2 + x kcal.

Lactic acid bacteria can be divided into two physiological and biochemical subgroups, differing in the products that are formed from glucose as a result of fermentation (this classification was proposed in 1925 by A.I. Kluiver, G.L. Donker): homofermentative and heterofermentative.

LACTIC ACID BACTERIA(syn. lactobacilli) - gram-positive rod-shaped bacteria belonging to the genus Lactobacillus (Beijerinck, 1901), family. Lactobacillaceae.

M. b. are represented by rods of various shapes: from short cocci-shaped to long thread-like (Fig.). The length of cells in different cultures of the same species depends on the composition of the medium, the presence of oxygen, and the method of incubation. M. b. reproduce. division by a septum, which leads to the formation of chains. Ultrafine cell structure of M. b. in many ways similar to other gram-positive bacteria. They form small colonies on agar media.

M. b. do not have cytochrome-containing respiratory systems, are immotile, do not form catalase, do not reduce nitrates to nitrites, do not liquefy gelatin, do not form spores and pigment; strict anaerobes or facultative. They have proteolytic activity due to the action of proteases and peptidases, but do not have lipolytic activity. The source of energy for M. b. is lactic acid fermentation (see). M. b. They are divided into homofermentative, which form up to 90% of lactic acid as a result of the fermentation of carbohydrates, as well as insignificant amounts of volatile acid, ethyl alcohol and carbon dioxide, and heterofermentative, which form approx. 50% lactic acid, 25% CO 2, 25% acetic acid and ethyl alcohol.

Systematics of M. b. not fully developed. Bergey’s Manual of Determinative Bacteriology (1974) includes 25 species in the genus Lactobacillus. The difficulty of classification lies in the variability of many properties of these microorganisms when cultivated in different media and under different conditions. A study of the nucleotide composition of DNA showed that the content of guanine and cytosine in the DNA of various species of M. b. varies and ranges from 34.2 to 53.4 mol. %.

Antigenic properties have not been studied enough; preliminary data have been obtained on the presence of antigens common to many types of M. b.

M. b. demanding of food sources, do not grow on simple media; grow on media containing plant decoctions, meat and yeast extracts, protein hydrolysates, because M. b. need amino acids, vitamins and a number of inorganic compounds; The pH of the media is within the range of 5.0-6.5, the optimum pH is 5.5. M. b. can grow at pH 3.8 and below. For cultivation of M. b. Rogosa medium or its modifications are widely used. Temperature range from 15 to 45° depending on the species.

M. b. found in the soil, concentrated around the root system, on cultivated and wild plants, in yellow-kish. tract of warm-blooded animals and birds, insects. In humans, they are found throughout the entire length of the gout. tract - from the oral cavity to the rectum. Representatives of M. b. (with few exceptions) are not pathogenic for humans. The most characteristic are L. acidophilus, L. plantarum, L. casei, L. salivarius, L. fermenti and L. brevis. L. bifidus in Bergey's Guide to Bacteria (1974) is allocated to a separate genus Bifidobacterium (see Bifidobacteria).

M. b. used in bakery, dairy industry, biol. canning many products (fermentation of vegetables and fruits), preparing kvass, ensiling. For the prevention and treatment of gland.-kish. diseases, vitamin deficiencies and nutritional anemias in animals, drugs are used, which also include M. b.

I. I. Mechnikov pointed to M. b. as antagonists of putrefactive and pathogenic microbes living in the human intestinal tract, and proposed their use in the fight against intestinal dysfunctions and premature aging. Many peoples use fermented milk products to treat burns and wounds, for the prevention and treatment of gallstones. diseases.

The development of microbiology has expanded the scope of application of these microorganisms: with the help of M. b. In industry, milk is obtained and used for the synthesis of dextran, used in medicine as a partial blood substitute; a number of antibiotics produced by these microbes have been identified; use M. b. when creating baby food products, including those used for medical purposes in newborns. Acidophilus paste is used in obstetrics and gynecology. practice, dermatology and surgery. L. acidophilus is included, along with B. bifidum and E. coli, in the complex drug “omniflora”, used abroad for the treatment of intestinal disorders. In our country, Lactobacterin (see) is produced, the active principle of which is lyophilized bacteria of the strains L. fermenti 90T-C4 and L. plantarum 8P-AZ, which have high antagonistic activity against pathogens of dysentery, enteropathogenic Escherichia coli, staphylococcus, Proteus, and bifidumbacterin (see).

Bibliography: Erzinkyan L. A. Biological features of some lactic acid bacteria, Yerevan, 1971; Kvasnikov E, I. and Nesterenko O. A. Lactic acid bacteria and ways of their use, M., 1975, bibliogr.; Krasilnikov N.A. Key to bacteria and actinomycetes, p. 208, M.-L., 1949; M e ch n i k o v I. I. Academic collected works, vol. 15, p. 247, M., 1962; Guide to vaccine and serum production, ed. P. N. Burgasova, p. 94, M., 1978; Bergey's manual of determinative bacteriology, ed. by R. E. Buchanan a. N. E. Gibbons, Baltimore, 1975; L e r s h e M. u. R e u t e r G. Das Yorkommen aerob wachsender grampositiver Stabchen des Genus Lactobacillus Beijerinck im Darmin-halterwachsener Menschen, Zbl. Bakt., I. Abt. Orig., Bd 185, S. 446, 1962; R o g o s a M., Mitchell J. A. a. Wiseman R. F. A selective medium for the isolation and enumeration of oral lactobacilli, J. dent. Res., v. 30, p. 682, 1951.

G. I. Goncharova.

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