Methods of protecting food products from spoilage. Product for protecting food products from spoilage, a method for protecting food products from spoilage. A method for protecting food products from spoilage.

In an effort to protect food products from spoilage, in ancient times man developed a method of preserving them (canning) by drying, smoking, salting and fermenting, pickling, and subsequently cooling and freezing, canning with sugar or using preservatives and heat treatment.

Let's consider these methods.

Drying. The preservative effect of drying food products is to remove moisture. When dried, the dry matter content of the product increases, which creates unfavorable conditions for the development of microorganisms.
Increased humidity in the room and air can cause deterioration of dried products - the appearance of mold. Therefore, they must be packaged in containers that exclude the possibility of increasing moisture in the product.

Smoking. This method is used for preparing meat and fish products. It is based on the preservative effect of some components of flue gases, which are obtained during the slow combustion of firewood and hardwood sawdust.
The resulting sublimation products (phenols, creosote, formaldehyde and acetic acid) have preservative properties and give smoked meats a specific taste and aroma.
The preservative effect of smoking substances is enhanced by preliminary salting, as well as partial removal of moisture during salting and cold smoking.

Salting. The preservative effect of table salt is based on the fact that at a concentration of 10 percent or more, the vital activity of most microorganisms ceases.
This method is used for salting fish, meat and other products.

Pickling. When food products are fermented, mainly cabbage, cucumbers, tomatoes, watermelons, apples and others, biochemical processes occur in these products. As a result of lactic acid fermentation of sugars, lactic acid is formed, and as it accumulates, conditions for the development of microorganisms become unfavorable.
The salt added during fermentation is not decisive, but only helps to improve the quality of the product.
To avoid the development of mold and putrefactive microbes, pickled products should be stored at low temperatures in a basement, cellar, or icebox.

Pickling. The preservative effect of pickling food products is based on creating unfavorable conditions for the development of microorganisms by immersing them in a solution of food acid.
Acetic acid is usually used for pickling foods.

Cooling. The preservative effect of cooling is based on the fact that at a temperature of 0°C most microorganisms cannot develop.
The shelf life of food products at 0°C, depending on the type of product and the relative humidity in the storage area, ranges from several days to several months.

Freezing. The basis for this storage method is the same as for refrigeration. Prepared products are quickly frozen to a temperature of minus 18-20°C, after which they are stored at a temperature of minus 18°C.
Complete freezing of the product occurs at a temperature of minus 28°C. This temperature is used for industrial storage, but in most cases it is not available at home.
When frozen, the vital activity of microorganisms stops, but when thawed they remain viable.

Canning with sugar. High concentrations of sugar in products of the order of 65-67 percent create unfavorable conditions for the life of microorganisms.
When the sugar concentration decreases, favorable conditions are again created for their development, and consequently, spoilage of the product.

Canning using preservatives. Antiseptics are chemical substances that have antiseptic and preservative properties. They inhibit the processes of fermentation and rotting and, therefore, contribute to the preservation of food products.
These include: sodium benzoate, sodium salicylic acid, aspirin (acetylsalicylic acid). However, it is not recommended to use them at home, since this method of preservation deteriorates the quality of the products. In addition, these substances are unacceptable in a regular diet.

Heat preservation. Canning, i.e. preserving food products from spoilage for a long time, is also possible by boiling them in a hermetically sealed container.
The food product to be preserved is placed in a tin or glass container, which is then hermetically sealed and heated for a certain time at a temperature of 100°C or higher or heated at 85°C.
As a result of heating (sterilization) or heating (pasteurization), microorganisms (molds, yeasts and bacteria) die and enzymes are destroyed.
Thus, the main purpose of heat treatment of food products in hermetically sealed containers is to defertilize microorganisms.
Food products in hermetically sealed containers do not undergo changes during the sterilization process. With other methods of canning (salting, drying, etc.), products lose their appearance and their nutritional value decreases.

General provisions

STERILIZATION AND PASTEURIZATION

Sterilization is the main way to preserve a food product without significant changes in its taste.

The method of sterilizing canned food in glass containers with immediate sealing with tin lids after boiling is very convenient at home. It provides the necessary tightness and vacuum in the rolled up jar, promotes the preservation of the canned product and its natural color.

Sterilization of products at home is carried out at the boiling point of water. Fruit compotes and vegetable marinades can be sterilized at a water temperature of 85°C (pasteurization). But in this case, pasteurized canned food should be in the sterilizer 2-3 times longer than in boiling water.

In some cases, for example, to sterilize green peas, when the boiling point of water during sterilization should be above 100°C, table salt is added to the water.
In this case, they are guided by the table (indicate the amount of salt in grams per 1 liter of water):

Amount of salt, g/l Boiling point °C
66 ..........................................................101
126..........................................................102
172..........................................................103
216..........................................................104
255..........................................................105
355..........................................................107
378..........................................................110

Canned food prepared at home is sterilized in a pan, bucket or special sterilizer. A wooden or metal grid is placed horizontally on the bottom of the dish. It eliminates the breakage of cans or cylinders during sterilization under sudden temperature fluctuations. You should not place rags or paper on the bottom of the sterilizer, as this makes it difficult to observe when the water begins to boil and leads to product rejection due to insufficient heating.

So much water is poured into the pan to cover the shoulders of the jars, that is, 1.5-2 cm below the top of their necks.

The temperature of the water in the pan before loading filled cans should be at least 30 and no more than 70 ° C and depends on the temperature of the loaded canned food: the higher it is, the higher the initial temperature of the water in the sterilizer. The pan with the jars placed in it is placed on high heat, covered with a lid and brought to a boil, which should not be violent during sterilization.

The time for sterilization of canned food is counted from the moment the water boils.

The heat source at the first stage of sterilization, that is, when heating the water and the contents of the jars, must be intense, since this reduces the time of heat treatment of the product, and it turns out to be of higher quality. If we neglect the speed of the first stage, the canned food produced will be overcooked and will have an unsightly appearance. The time for heating water in a saucepan to a boil is set: for cans with a capacity of 0.5 and 1 liter - no more than 15 minutes, for 3-liter jars - no more than 20 minutes.

At the second stage, that is, during the sterilization process itself, the heat source should be weak and only maintain the boiling point of water. The time specified for the second stage of sterilization must be strictly adhered to for all types of canned food.

The duration of the sterilization process depends mainly on the acidity, thickness or liquid state of the product mass. Liquid products are sterilized within 10-15 minutes, thick ones - up to 2 hours or more, acidic products - less time than non-acidic ones, since an acidic environment is not conducive to the development of bacteria.

The time required for sterilization depends on the volume of the container. The larger the container, the longer the boiling takes. It is recommended to write down the start and end times of sterilization on a separate sheet of paper.

At the end of sterilization, the jars are carefully removed from the pan and immediately sealed with a key, checking the quality of the sealing: whether the lid is rolled well, whether it is not turning around the neck of the jar.

Sealed jars or cylinders are placed neck down on a dry towel or paper, separating them from one another, and left in this position until cooled.

Steam sterilization
Canned food is sterilized with steam in the same container where water is boiled for this purpose. The amount of water in the pan should not exceed the height of the wooden or metal grate - 1.5-2 cm, since the less water, the faster it heats up.
When the water boils, the resulting steam warms the jars and the contents in them. To prevent steam from escaping, the sterilizer is tightly closed with a lid.
The time required to bring the water in the sterilizer to a boil is 10-12 minutes.
The time required to sterilize canned food with steam is almost twice as long as when sterilizing in boiling water.

Pasteurization
In cases where it is necessary to sterilize canned food at a temperature below boiling water, for example for marinades, compotes, they are cooked at a water temperature in a pan of 85-90°C. This method is called pasteurization.
When cooking canned food using the pasteurization method, it is necessary to use only fresh, sorted fruits or berries, thoroughly washed from dust; strictly adhere to the temperature and time of pasteurization; Before laying the container, wash it thoroughly and boil it.
The preservation of canned food prepared by pasteurization is facilitated by the presence of high acidity.
You can pasteurize cherries, sour apples, unripe apricots and other sour fruits for preparations and compotes.

Repeated sterilization
Repeated or multiple (two to three times) sterilization of the same jar of food products containing large quantities of protein (meat, poultry and fish) is carried out at the boiling point of water.
The first sterilization kills mold, yeast and microbes. During the 24-hour period after the first sterilization, the spore forms of microorganisms remaining in the canned food germinate into vegetative forms and are destroyed during secondary sterilization. In some cases, canned food, such as meat and fish, is sterilized a third time a day later.
To re-sterilize at home, you must first seal the jars and put special clips or clips on the lids so that the lids do not come off the jars during sterilization.
The clamps or clips are not removed until the cans have completely cooled (after sterilization) to avoid the lids falling off and possible burns.

Sterilization of canned food, previously hermetically sealed
For this method of sterilization, it is necessary to have special metal clips or clips to secure the sealed lids on the jars. This prevents their breakdown during the sterilization process as a result of the expansion of the mass of the canned product, as well as the air remaining in the jar during heating.
The use of special clamps allows you to stack jars in the sterilizer in 2-3 rows.
A vacuum is formed in jars that are hermetically sealed prior to sterilization. It should be remembered that the higher the temperature of the product in the jar at the time of capping, the greater the vacuum obtained.

Hot canning of liquid products without subsequent sterilization
Canning liquid products that have been previously boiled or brought to a boil can be done by hot packaging without subsequent sterilization. Using this method, tomato juice, crushed tomatoes, grape, cherry, apple and other juices, plum preparations for jam, fruit puree from sour fruits, etc. are prepared.
Glass containers - jars and their lids - should be thoroughly washed and steamed in a steam-water bath for 5-10 minutes.
The temperature of the product before filling the jars must be at least 96°C. The jars must be hot when filled with product. Immediately after filling them with the canned product, they are capped.
With this method of canning, sterilization occurs due to the heat transferred to the product and container when they are boiled, and the safety of canned food depends on the quality of the raw materials and its processing.

Hot canning of fruits and vegetables without subsequent sterilization
This method is used for canned vegetables - cucumbers, tomatoes, as well as for fruit preparations and compotes from whole fruits.
For this method of canning, the raw materials must be fresh, thoroughly washed and sorted.
According to this method, canned food is prepared in the following sequence: vegetables or fruits placed in jars are carefully poured with boiling water in 3-4 additions. After pouring in a portion of boiling water, the jar is turned to heat the walls so that the glass does not crack due to sudden temperature fluctuations.
The jars filled with boiling water are covered with a clean lid, wrapped in a towel and kept for 5-6 minutes. Then the water is drained and the jar is again filled with boiling water, covered again with a lid and kept for another 5-6 minutes. If necessary, this operation is repeated a third time.
After the second and third soaking, the water is drained and immediately poured with boiling marinade - for cucumbers and tomatoes, boiling water - for fruit preparations and boiling syrup - for compotes.
Then immediately cover with a lid, seal and check the quality of the seal.
After capping, the jar is placed upside down. Cooling is in air.

General provisions

CONDITIONS, SPICES AND SPICES
FOR CANNING

Seasonings and spices are used in home canning to improve the taste, aroma, and often the color of prepared products. A moderate amount of them has a beneficial effect on the taste of food, and also increases the secretion of digestive juices, thereby promoting better absorption of food.
An excessive dose of spices and herbs can cause serious irritation of the gastric mucosa. Therefore, when using seasonings, herbs and spices, it is recommended to be in moderation.

Table salt is the main seasoning necessary for a healthy body and is most often used when preparing food at home.

Vinegar is also an indispensable component for canning.
The most common types of vinegar are table wine, flavored tarragon, grape, apple, etc.
In most cases, the most successful, which does not impart any additional flavors to the product, is alcohol vinegar.
Most often, synthetic acetic acid (acetic essence) diluted with water is sold under the name “vinegar”.
All types of vinegar labeled "flavored" are synthetic vinegar with some synthetic additives.
Store vinegar in a glass container with a tightly closed lid at a temperature of 5 °C.

Citric acid is odorless, and therefore it is recommended to use it when preparing products whose taste does not match the smell of vinegar: compotes, jellies, etc.

Black and white peppers are the dried seeds of a climbing tropical shrub, collected at various stages of maturity. They differ from each other in color, pungency and sharpness of smell (black is more pungent).
When preparing food, pepper is used both in the form of peas and ground. The latter quickly loses its nutritional qualities during long-term storage, so it is recommended to grind the pepper as needed.
Used for pickling, salting, pickling, etc.

Allspice looks like black pepper and appears as dark brown peas. It has a strong pleasant aroma and relatively little pungency.
Used in various types of home canning.

Red pepper is the fruit of a herbaceous plant that resembles a large pod in appearance. Contains many vitamins, in particular vitamin C, surpassing even lemon in vitamin content.
Depending on the amount of a special substance - capsaicin - which gives red pepper its pungency and pungency, sweet (paprika) and bitter peppers are distinguished.
Paprika is a large, fleshy fruit.
The fruits of bitter pepper have an elongated shape. In terms of its pungency and pungency, it can only be compared with black pepper. Can also be used in powder form.

Bay leaves are dried leaves of the noble laurel tree, which are highly aromatic. The main purpose of bay leaves is to flavor food without giving it any pungency or bitterness.
Excess bay leaves change the taste of the dish for the worse, giving it a too strong smell.
When cooking, it is added at the end, since with prolonged heat treatment it gives a bitter taste.

Cloves are the dried, unopened flower buds of the clove tree.
Cloves get their specific aroma thanks to the valuable essential oils it contains.
Used for pickling, salting and other types of canning.
It is recommended to add cloves shortly before the end of cooking and in small quantities, since even a small dose of cloves gives the product a pronounced aroma.

Coluria. The smell of coluria is close to the smell of cloves. For home canning, it is used instead of cloves in the form of dried roots ground into powder.

Cinnamon is the peeled and dried bark of the shoots of the cinnamon tree. Used in powder or pieces.
When canning at home, it is used to flavor marinades, jams, compotes, etc.

Saffron is the dried stigmas of crocus flowers and has a specific aroma.
Used as a flavoring and coloring agent.

Nutmeg. Nutmeg seeds, shelled and dried.
It has a very pungent and pungent taste and aroma.

Vanilla and vanilla. The first is the fruit of a tropical orchid, which in appearance resembles a pod with very fragrant small seeds inside. Vanillin is a synthetic powder - a substitute for vanilla.
It is used for canning fruits and berries that have a weak aroma of their own (for example, cherry jam).
Excess vanilla and vanillin gives the product a bitter taste.

Ginger. Tropical nut root, peeled and dried. It is used in crushed form and has a pleasant smell and pungent taste.
It is recommended to store it uncrushed, which allows it to better preserve its aroma.

Dill. Young plants in the rosette phase are used as an aromatic seasoning for salads, soups, meat, fish, mushroom and vegetable dishes.
Adult plants in the seed formation phase are used as the main type of spice for pickling and pickling cucumbers, tomatoes, and sauerkraut.

Mint is quite widely used in homemade preparations due to its pleasant aroma and refreshing taste.
Mint is added when preparing fish, meat, vegetables, and when making kvass. Can be used both fresh and dried.

Coriander is the dried seeds of the herbaceous plant coriander.
Used in pickling, flavoring vinegar, etc.

Basil has a delicate aroma with various shades.
Used fresh and dried for adding to vegetable marinades.

Tarragon is the dried stems and leaves of the herbaceous plant of the same name.
Used for salting, pickling, etc.

Canning, like any reasonable intervention that is applied to raw materials during storage, does not destroy its natural properties. At the same time, it is necessary to pay attention to other immediate tasks, such as, for example, the preservation of nutritional value, the preservation of the most important organoleptic properties - appearance, smell, taste and consistency - and the greatest limitation of losses of the most important constituent substances, especially vitamins. This effect can be achieved in different ways. Each canning method has its own advantages and disadvantages, some have their own specific features, others require a mandatory set of products. For the needs of home canning, we will analyze only those methods that can be implemented from the point of view of available canning equipment.

As already mentioned, the first cause of food loss is the activity of microorganisms and all methods of canning are intended to stop this.

One of the most common answers why people don't eat healthy food is because it's expensive. While stocking up on fresh food, people end up throwing away a significant part of it, which means they are throwing money down the drain. Luckily, there are ways to keep your supplies fresh for a long time. Say goodbye to wilted lettuce, moldy mushrooms and sprouted potatoes. And you will see that investing in healthy products is worth every penny.

Problem: Overripe bananas

Solution: Wrap banana stems in plastic wrap

There are fruits that, when ripe, emit ethylene gas - bananas are one of them. If you know you won't eat them right away, simply wrap the stems (where most of the gas is released) tightly in plastic wrap. This will slow down the ripening process and keep the fruits fresh for a long time. Bananas, melons, nectarines, pears, plums and tomatoes also emit ethylene and should be stored away from other foods.

Problem: Soft celery

Solution: Wrap in foil and store in the refrigerator

Celery is a product that can quickly turn from strong and crunchy to soft and limp. You only need to spend a few minutes to extend its service life. After washing and drying the stems, wrap it in aluminum foil. This will retain moisture, but will release ethylene, unlike plastic bags. This way you can keep celery fresh for several weeks.

Problem: Wilted lettuce

Solution: Cover the bottom of the refrigerator container with paper towels.

Everyone wants a healthy, crunchy salad on the summer dinner table. But after a few days it fades. To extend the shelf life of greens and other foods in your refrigerator, line the drawer with paper towels. Moisture is what makes fruits and vegetables wilt. The paper in the vegetable compartment of the refrigerator will absorb excess moisture and keep the food fresh for a long period of time.

Problem: Moldy berries

Solution: Wash the berries in vinegar and place in the refrigerator

In summer, store shelves are full of bright and juicy berries. Low seasonal prices for strawberries, blueberries, and raspberries make it tempting to buy a larger package. But if they are not eaten quickly, the berries become soft and sticky. To avoid this, rinse the berries with a vinegar solution (one part vinegar to three parts water) and then with clean water. Once dry, store the berries in the refrigerator. Vinegar kills bacteria on the berries and prevents mold growth, allowing them to last longer.

Problem: Sprouted potatoes

Solution: Store potatoes with apples

A big bag of potatoes can be a lifesaver during busy days. It can be quickly made into baked potatoes, fries or pancakes. The disadvantage of such a stock is that the potatoes begin to sprout. It should be stored in a cool, dry place, away from sunlight and moisture. And one more trick: throw an apple into a bag of potatoes. There is no scientific explanation for this phenomenon, but the apple protects the potatoes from sprouting. Try it and judge for yourself.

Problem: Slippery mushrooms

Solution: Store mushrooms not in plastic, but in a paper bag

Mushrooms are a tasty and nutritious ingredient in many dishes, but nothing is more unappetizing than a slimy mushroom. To keep mushrooms meaty and fresh for as long as possible, you need to store them properly. We have a habit of packing everything in plastic bags, but mushrooms need paper. Plastic retains moisture and allows mold to develop, while paper breathes and allows moisture to pass through, and, therefore, slows down the spoilage of mushrooms.

In an effort to protect food products from spoilage, in ancient times man developed a method of preserving them (canning) by drying, smoking, salting and fermenting, pickling, and subsequently cooling and freezing, preserving with sugar or using preservatives and heat treatment.
Drying. The preservative effect of drying food products is to remove moisture. When dried, the dry matter content of the product increases, which creates unfavorable conditions for the development of microorganisms.
Increased humidity in the room and air can cause deterioration of dried products - the appearance of mold. Therefore, they must be packaged in containers that exclude the possibility of increasing moisture in the product.

Smoking. This method is used for preparing meat and fish products. It is based on the preservative effect of some components of flue gases, which are obtained during the slow combustion of firewood and hardwood sawdust. The resulting sublimation products (phenols, creosote, formaldehyde and acetic acid) have preservative properties and give smoked meats a specific taste and aroma.
The preservative effect of smoking substances is enhanced by preliminary salting, as well as partial removal of moisture during salting and cold smoking.

Salting. The preservative effect of table salt is based on the fact that when it is concentrated in an amount of 10 percent or more, the vital activity of most microorganisms ceases. This method is used for salting fish, meat and other products.

Pickling. When food products are fermented, mainly cabbage, cucumbers, tomatoes, watermelons, apples and others, biochemical processes occur in these products. As a result of lactic acid fermentation of sugars, lactic acid is formed, and as it accumulates, conditions for the development of microorganisms become unfavorable.
The salt added during fermentation is not decisive, but only helps to improve the quality of the product. To avoid the development of mold and putrefactive microbes, pickled products should be stored at low temperatures in a basement, cellar, or icebox.

Pickling. The preservative effect of pickling food products is based on creating unfavorable conditions for the development of microorganisms by immersing them in a solution of food acid.
Acetic acid is usually used for pickling foods.

Cooling. The preservative effect of cooling is based on the fact that at 0 degrees most microorganisms cannot develop. The shelf life of food products at 0 degrees, depending on the type of product and the relative humidity in the storage area, ranges from several days to several months.

Freezing. The basis for this storage method is the same as for refrigeration. Prepared products are quickly frozen to a temperature of minus 18-20 degrees, after which they are stored at a temperature of minus 18 degrees.
When frozen, the vital activity of microorganisms stops, but when thawed they remain viable.

Canning with sugar. High concentrations of sugar in products of the order of 65-67 percent create unfavorable conditions for the life of microorganisms. When the sugar concentration decreases, favorable conditions are again created for their development, and consequently, spoilage of the product.

Canning using preservatives.
Antiseptics are chemical substances that have antiseptic and preservative properties. They inhibit the processes of fermentation and rotting and, therefore, contribute to the preservation of food products.
These include: sodium benzoate, sodium salicylic acid, aspirin (acetylsalicylic acid). However, it is not recommended to use them at home, since this method of preservation deteriorates the quality of the products.

Heat Canning. Canning, i.e. preserving food products from spoilage for a long time, is also possible by boiling them in a hermetically sealed container.
The food product to be canned is placed in a tin or glass container, which is then hermetically sealed and heated for a certain time at a temperature of 100 degrees or higher or heated at 85 degrees.
As a result of heating (sterilization) or heating (pasteurization), microorganisms (molds, yeasts and bacteria) die and enzymes are destroyed.
Thus, the main purpose of heat treatment of food products in hermetically sealed containers is to sterilize microorganisms.
Food products in hermetically sealed containers do not undergo changes during the sterilization process, their taste and nutritional value are preserved. With other methods of canning (salting, drying, etc.), products lose their appearance and their nutritional value decreases.

Preservation of food products from spoilage is carried out mainly in two ways. The first method on which food preservation in hermetically sealed containers is based is sterilization. The product is heated to destroy microorganisms and is placed in an airtight container to protect it from subsequent contamination. The second method ensures the preservation of the food product by inhibiting the development of microorganisms that cause spoilage; this goal can be achieved by various processing of the food product, as a result of which the activity of microorganisms is delayed or slowed down. Processing a product with such methods is not always associated with the destruction of microorganisms (i.e., it does not provide a germicidal or fungicidal effect); when the effect that inhibits the development of microorganisms is eliminated or reduced, the food product is subject to spoilage.

When considering the relationship between the vital activity of microorganisms and methods of food preservation, it is necessary to pay attention to the most common of them, which do not require heating, since products processed by such methods are often used as raw materials in the production of canned food. In addition, the preservation of some foods (fruit, jam, sauces and marinades) is carried out using both heat and retarding agents. The main methods used on an industrial scale include: freezing, gas storage, drying (dehydration), filtering, pickling, pickling, smoking, irradiation and the addition of so-called natural preservatives - sugar, salt, acids and spices and chemical preservatives - sulfur dioxide and benzoic acid. Some of these methods are used in combination with one another, and their effect is cumulative.

Freezing

At low temperatures, food products are preserved by inhibiting or preventing the growth of spoilage microorganisms; If these products are completely fresh, then the action of natural autolytic enzymes is delayed.

Microorganisms that grow at 0°C and below have an optimum within 15-20°C; microorganisms with an optimum of about 37° give very slow growth (or no growth at all) at temperatures below 5°. Psychrophilic microorganisms are capable of relatively rapid growth at 0°C; Moreover, although the intensity of their growth is lower than at higher temperatures, the total number of cells formed can be quite large. Microorganisms that typically grow at low temperatures are bacteria of the genera Achromobacter, Flavobacterium, Pseudomonas and Micrococcus; yeasts of the Torulopsis type and molds of the genera Penicillium Cladosporium, Mucor and Thamnidium.

The lower limit at which the growth of microorganisms in food products occurs is determined not only by temperature: a very important factor is the amount of water frozen out of the medium. During the formation of ice, the growth of bacteria is retarded, while molds and yeasts predominate under these conditions, since they better withstand the high osmotic pressure resulting from the concentration of dissolved substances due to the separation of water in the form of ice. For the same reason, bacterial growth on a supercooled medium occurs at lower temperatures than on a frozen medium. Bacterial growth on a supercooled medium can occur at -7. °, while the maximum growth temperature on frozen media is about -3° Microorganisms that can withstand high concentrations of solutes can be extremely resistant to low temperatures; growth of halophilic bacteria on bacon and osmophilic yeast in concentrated orange juice has also been noted. at temperatures down to -10°.

The maximum growth temperature for psychrophilic microorganisms, including bacteria, yeasts and molds, ranges from -5° to -10°, closer to -7°. It has been established that storage at -5° does not prevent the development of yeast and mold on frozen meat, and colonies appear after 7 weeks. The growth of Pseudomonas, Lactobacillus, Monilia and Peicillium occurred at -4°, and Cladosporium and Sporotrichum - at -6.7°. Most foods stored below the temperature range of -5 to -7° can be considered frozen (i.e., do not contain a liquid phase to support the growth of microorganisms).

Freezing initially causes a rapid decline in the number of viable microorganisms. Depending on the temperature, the nature of the environment, the type of microorganisms and other factors, the number of surviving microorganisms may then undergo a further slow decline or (for psychrophilic microorganisms) the initial decline may be followed by a period of delayed reproduction and then growth of the surviving microorganisms. Extreme pH values ​​increase the sensitivity of microorganisms to cold, while the presence of sugars, glycerol and colloids has a protective effect. These data do not apply to bacterial spores, which are virtually resistant to cold treatment or frozen storage.

Regarding the reason for the death of bacteria after cold treatment, the opinions of researchers differ: some explain it by the direct influence of cold, causing the death of bacteria, others by mechanical damage by extracellular and intracellular ice crystals, and still others by changes in the proteins contained in the cells. For detailed information, it is advisable to refer to works that provide detailed content of various theories regarding the death of bacteria under the influence of low temperatures. Most researchers indicate that the number of dying bacteria does not increase with decreasing temperature; Haynes found that the death of bacteria was more rapid at -1 to -5° than at -20°; other researchers observed the same phenomenon: bacteria and yeast were more destroyed at -10° than at -20°. When studying the process of survival of microorganisms on frozen meat, it was found that the number of coli bacteria decreased slightly during storage at -18°, but decreased 10 times after storage at -4°.

In general, microorganisms are extremely resistant to low temperatures, even pathogenic species survive for long periods. Many types of bacteria and some types of molds and yeasts survived in frozen strawberries for 3 years. When studying pathogenic bacteria in quickly frozen strawberries (-18°), it was found that Eberthella lyphosa survives 6 months, Staphylococcus aureus - 5 months and bacteria like Salmonella - 1 month.

A comprehensive review of research on the effects of freezing on microorganisms was published in 1955.

Gas storage

A significant reduction in the number of microorganisms that cause spoilage is achieved by changing the composition of the air in the room where food products are stored. Inhibition of the growth of obligate aerobes, such as molds, can be achieved by storage under completely anaerobic conditions, but some molds can tolerate very low oxygen levels; It has been established that the oxygen demand of mold fluctuates greatly.

Industrial methods, such as vacuum packaging and inert gas packaging, prevent rancidity and other oxidative reactions, but do not completely inhibit mold growth.

During refrigerated storage of raw (fresh) food products (meat, eggs, fruits, vegetables), the introduction of carbon dioxide, ozone, sulfur dioxide or nitrogen trichloride into the storage atmosphere inhibits the growth of microorganisms, thereby increasing the safety of food products.

The germination of mold spores is delayed when the air contains 4% carbon dioxide; at a 20% carbon dioxide content, the growth rate of microorganisms is 1/2-1/5 compared to storage in air, and the inhibition of growth is more pronounced the lower the temperature. To completely inhibit the growth of molds and bacteria on meat, a 40% carbon dioxide content is optimal, but this concentration has a negative effect on the quality of meat (loss of color).

At 20% concentration and moderate shelf life, the color of the meat changes very little, and the growth of spoilage microorganisms is still retarded to a significant extent. In practice, a 10% carbon dioxide concentration is used; under such conditions, chilled meat is not subject to microbial spoilage for 60-70 days. The use of carbon dioxide in low concentrations makes it possible to extend the shelf life of chilled pork and lamb. Experiments on storing eggs in the presence of carbon dioxide have established the need to balance favorable and unfavorable conditions, a review of which is given in the above work.

Respiration and fruit ripening may be delayed by storage in an atmosphere low in oxygen and high in carbon dioxide. Due to the fact that overripe fruits are susceptible to microbial spoilage, the use of carbon dioxide in combination with cold storage has been practiced to prevent spoilage of pome fruits - apples and pears. The concentration required for this varies depending on the type and even variety (pomological) of the fruit; Typically, fairly high concentrations of carbon dioxide are required to prevent fruit rot.

The advantages and disadvantages of atmospheric ozonation are highlighted in a review published in 1938. The main and quite obvious objection to the use of such a strong oxidizing agent as ozone is the rancidity of products (meat, bacon, sausages, cream, butter, egg powder, etc. ) even at ozone concentrations ranging from 50-100 parts per million parts of air (0.005%-0.01%). At freezing temperatures, a concentration of 0.0003% is sufficient to inhibit the growth of molds and bacteria, but prolonged exposure to ozone, even at such low concentrations, causes butter and other foods to go rancid. An equilibrium concentration of 0.0003% ozone has almost the same germicidal effect whether applied continuously for two two-hour periods or one three-hour period per day.

By using such short-term exposures, many types of food products can be successfully stored. For storing beef meat at refrigeration temperatures, exposure to 0.00025-0.0003% ozone for two-hour periods twice daily is recommended; under such conditions, the shelf life can be extended from two to eight weeks. Some researchers have reported that microorganisms can acclimate to ozone atmospheres. However, the author of the above review states that despite numerous studies, he has not observed such a phenomenon in molds on beef meat.

Ozonation has proven to be most effective in egg storage, where evaporative drying is difficult unless proper relative humidity is maintained. If the relative humidity of the air is increased to prevent this shrinkage, the eggs quickly begin to mold, and ozone is very effective in combating this type of spoilage. Assuming normal cleanliness of eggs, to prevent molding, the presence of a minimum concentration (0.00006%) of ozone in the air of the room in which boxes of eggs are stored is required, and at the same time it is possible to store eggs for eight months at -0.6 ° and 90% relative humidity; After this period, the freshness of the eggs does not differ at all from those stored for several days. According to Summer, the bactericidal activity of ozone increases significantly with increasing relative air humidity, but is practically reduced to zero if this humidity is below 50%.

Ozone is very effective in increasing the shelf life of raw fruits (strawberries, raspberries, grapes, etc.), but it does not prevent rotting of citrus fruits.

In 1950, work was published showing that grape spoilage caused by the Botrytis mold was reduced by alternating applications of sulfur dioxide (2% concentration) and freezing. Nitrogen trichloride was also used to combat mold on citrus fruits and other products. The disadvantage of both gases is their high corrosive effect; in addition, nitrogen trichloride is unstable and must be regenerated as needed.

In connection with gas storage, it should be noted that the shelf life of any product is determined mainly by its initial microbial contamination. To obtain the maximum effect from gas storage, it is necessary to take all precautions against contamination of the product before storing it. To destroy a large number of actively growing microorganisms, a significantly higher concentration of ozone is required than for small quantities.

Reducing the moisture content of the product

Both dehydration (drying) and sugar addition can be considered under this heading, since both of these operations reduce the moisture content to a level at which microbial growth is prevented.

With the exception of osmophilic yeasts, the study of which presents a special challenge, molds are less demanding in terms of moisture than other microorganisms. Therefore, for food to be preserved satisfactorily, its moisture content must be below the minimum that allows mold growth.

The true indicator of a product's sensitivity to mold is not its total moisture content, but rather its availability. For example, in jam, moisture is not sufficiently available for mold growth, while in grain products, moisture can be better used by them, despite its lower content. Water availability is most conveniently expressed in terms of equilibrium moisture content.

The minimum relative humidity required for the development of common types of mold varies depending on the type of mold in the range of 75-95%, with Aspergillus and Penicillium species being the most resistant to low relative humidity. The critical relative humidity for mold growth on flour is 75%. Experiments have established that critical relative humidity increases with decreasing temperature; mold growth is retarded: at 20°, if the relative humidity is 79% (moisture content 16%); at 15°, if the relative humidity is 82.5% (moisture content 16.5%); at 5°, if the relative humidity is 85% (moisture content 17.4%). The lowest relative humidity at which mold growth was observed was 85%. Experiments conducted in 1943 established that the minimum relative humidity for mold growth on dehydrated meat was slightly below 75%. The author of this book observed the presence of molds on jam at 74% relative humidity, but no growth at lower relative humidity. A study of the mold susceptibility of many products showed that at a relative humidity of 75%, there was only minor mold growth on cheese after one year of storage. Based on this, it was concluded that the water absorption properties of the product play an important role in determining the maximum relative humidity that allows mold growth. Mushrooms for the development of mycelium are able to receive moisture directly from the atmosphere only at 100% relative air humidity.

The presence of toxic substances, the pH of the environment, and the nutritional value of the product for mold influence the value of the maximum permissible humidity, but it can be argued that food products for which the relative humidity is below 74% are, as a rule, resistant to mold. Therefore, peas, grains and similar dry foods must be dehydrated to a moisture content where the equilibrium moisture content is below the specified limit. Similarly, in foods preserved with sugar, the solutes (sugar) must be present in a concentration sufficient to reduce the relative humidity to the level necessary to inhibit mold growth.

Fluctuations in temperature during storage may contribute to the molding of food in hermetically sealed containers, as sudden cooling may cause temporary localized condensation or excess moisture above equilibrium for the product.

At equal concentrations, the lower the molecular weight of the sugars, the higher the osmotic pressure of sugars in solution. Since the vapor pressure of solutions decreases with increasing osmotic pressure, monosaccharides (glucose, fructose) have a greater effect on reducing air humidity than sucrose. Thus, jam containing 65% sugar in the form of sucrose is more susceptible to molding than a similar product also containing 65% sugar, but in which part of the latter is invert sugar. When studying the preservative effect of various sugars, it was found that in relation to bacteria, the effectiveness of sugars is in the following order: fructose > glucose > sucrose > lactose. Thermophilic bacteria are more sensitive to the action of sugars than streptococci. For yeast development, fructose and glucose were equally effective at concentrations 5-15% lower than sucrose. The order of effectiveness of sugars against planoacid thermophiles is: glucose > fructose > sucrose. In relation to yeast and molds, the inhibitory effect of glucose is stronger than that of sucrose taken in equal concentration. A mixture of equal amounts of different sugars had inhibitory properties that were intermediate compared to individual types of sugar.

Osmophilic yeast can withstand high concentrations of sugar and cause spoilage of honey, chocolate fillings, jam, molasses and other products in which the sugar content reaches 80%. The most active agents of spoilage are yeasts belonging to the genus Saccharomyces according to the classification of yeasts proposed in 1952. Confectionery products with a relative vapor pressure on their surface of less than 69% are resistant to spoilage by osmophilic yeasts. A simple method has been developed for determining the relative vapor pressure on the surface of confectionery products by the degree of spreading of various crystals under the influence of one or another equilibrium humidity. For foods low in protein, the critical humidity at which fermentation occurs is significantly lower than for foods rich in proteins. It has been established that for products with humidity above the critical point, the addition of 10% invert sugar in many cases causes a significant decrease in the relative vapor pressure on the surface of these products. American researchers have compiled a table of equilibrium vapor pressure for various sugar solutions and given an empirical formula with which one can calculate the equilibrium vapor pressure of jams, chocolate cream, butter caramel, etc. The role of osmophilic yeast in food spoilage is well covered in works of 1942 and 1951.

Preserving most types of canned food in airtight containers by controlling moisture content is hardly possible. Similar controls, however, apply to some products preserved in tin and glass containers, for example, grain products (oatmeal, semolina) and those made with sugar (jam, candied fruits, candies and sweetened condensed milk). As a rule, sweet condensed milk is not sterile, but the microorganisms present in it are not capable of growth. Some types of jam and marmalade with a relatively low sugar content (about 60%) should be cooked to prevent spoilage.

Use of salt

The mechanism of action of salt as a food preservative has not yet been sufficiently studied, but, apparently, it is not only an osmotic effect. According to Speigelberg, the osmotic pressure at which bacterial growth stops is significantly lower for salt than for sugars. The concentration of salt required to inhibit the growth of microorganisms in a food product depends on a number of factors, including pH, temperature, protein content and the presence of inhibitory substances such as acids. Water content is of primary importance, and it is the concentration of water in the aqueous phase that is most important, not the content of the entire product. The inhibitory effect of salt on bacterial growth increases when the temperature decreases from 21 to 10°. Another paper provides data showing that the amount of salt required to inhibit mold growth decreases with decreasing temperature, with 8% salt being sufficient at 0°C, while 12% salt is required at room temperature. The influence of the composition of the medium on the resistance of microorganisms to the action of salt has been repeatedly proven: in 1939, a report was published that microorganisms found higher resistance to the action of salt in cucumber brine than in broths with the same salt content; Later it was found that the growth of halophilic bacteria can be stimulated or inhibited by varying the protein content in the medium. The effect of pH on salt tolerance was studied by Joslin and Cruess in 1929; They found that lowering pH values ​​caused a sharp decrease in salt tolerance in various species of yeasts and molds.

The German researcher Schup proposed dividing bacteria into three groups in relation to the effect of salt on them:

1) non-halophilic - do not grow at high salt concentrations;

2) obligate halophiles - growing only at high salt concentrations;

3) facultative halophiles - growing at high and low salt concentrations.

However, more recent work has cast doubt on the existence of true obligate halophiles. The halophiles studied by these researchers did not develop on low-salt media when 30-day-old or older cultures were used as inoculum. Another researcher has shown (contrary to the generally accepted view that halophilic bacteria live exclusively in salty environments, such as salt obtained by natural evaporation of water, sea water, on fish) that in fact halophilic bacteria are widespread in nature and can be isolated in the environment with 25% salt from non-salt materials including standing water, sulfur springs, manure and soil, subject to an incubation period of 90 days.

The wide variety of halophile types reported in the literature shows that there is no typical halophilic flora, but many microorganisms with a wide variety of morphological and biochemical properties. The growth of one or another species can occur at different salt concentrations, up to a saturated state. Pathogenic microorganisms are generally more sensitive to the action of strong salt solutions than saprophytic species, and rod-shaped microorganisms are more sensitive than cocci. Tanner and Evans reported that growth of Clostridium botulinum ceased at salt concentrations of 6.5-12%, with the critical concentration depending on the medium. A report has also been published on the suppression of the growth of Clostridium welchii and Cl. sporogenes at 5.7-7.4% salt content, and again the critical concentration depended on the environment. The growth of Clostridium Saccharobutyricum slows down when the medium contains 2.9-5.3% salt. Nunheimer and Fabian found that sodium chloride at 15-20% concentration prevents the growth of some food poisoning-causing staphylococci, and concentrations of 20-25% are lethal to them.

Livingston assumed that the spherical shape represents the smallest surface area for water exchange and is therefore desirable in concentrated solutions; It should be noted that micrococci as a group usually exhibit high salt tolerance and many of their species develop freely in the presence of 25% salt.

Many types of bacteria that grow in strong salt solutions are chromogenic and cause spoilage of salted fish and skins, changing their color. The non-syllable-forming anaerobic rod, isolated and described by Baumgartner, developed in an environment saturated with salt. This microorganism is the causative agent of spoilage with the formation of gas in unsterilized salted fish products - pates and fish sauces. This spoilage can be completely prevented by lowering the pH value of such products to 5.5 or lower.

Filmy yeast grows in solutions containing 24% salt. Yeast of this species grows on the surface of vegetable marinade brines and, by oxidizing lactic acid formed during the fermentation of vegetables, thereby reducing the stability of these products. Molds can exhibit the same unwanted activity. According to Tanner, mold growth can occur in the presence of 20-30% salt.

In connection with curing meat, it has been noted that many microorganisms can tolerate high salt concentrations in brines containing large pieces of meat; Apparently, growth occurs at the interfaces between brine and animal tissue and occurs very slowly in pure brine. At present, there is still very little data on such growth.

Application of acids

The effect of acids in preventing the growth of microorganisms may be due to the concentration of hydrogen ions or due to the toxicity of undissociated molecules or anions. In relation to mineral acids, the toxic effect is associated with the concentration of hydrogen ions; The toxicity of organic acids is not proportional to the degree of their dissociation and is mainly due to the action of undissociated molecules or anions.

Yeasts and molds are much less sensitive to the effects of high concentrations of hydrogen ions than bacteria. The optimal pH values ​​for most bacterial species are in the neutral zone, and bacteria are unable to grow at a pH below 4.5. The most acid-resistant bacteria are the Lactobacillus and Clostridium butyricum groups, growing at a pH of about 3.5; molds and yeasts that grow best at a pH of 5.0-6.0 can tolerate a pH of 2.0 or even lower.

Acetic and lactic acids are most widely used for food preservation. Research has found that acetic acid is a better preservative than lactic acid for marinades; It is also known that acetic acid is more toxic to bacteria, yeast and molds than lactic acid. When the medium is acidified with acetic acid, bacterial growth is inhibited at pH 4.9, Saccharomyces cerevisae - at pH 3.9, Aspergillus niger - at pH 4.1; the corresponding titratable acidities are 0.04, 0.59 and 0.27%. It should be noted that the indicated acidity values ​​refer to the inhibition of growth of several species in a medium prepared in the laboratory; in industrial practice, higher concentrations of acetic acid (1.5-2%) are required to prevent spoilage of products such as sauces, marinades, etc.

Adding 5% salt or 20.1% sugar does not significantly reduce the amount of acid required to prevent microbial growth. In non-toxic concentrations, acetic acid stimulates the growth of molds, providing them with an energy source. The following order of acids according to their preservative and germicidal effect on bacteria has been established (based on the pH value): acetic > citric > lactic acid; by amount of acid: lactic > acetic > citric; for yeast: acetic > lactic > citric acid, regardless of pH or acid concentration. It is also noted that the combination of sugar with the appropriate amount of acid makes this mixture germicidal. In work with planoacid thermophiles, the following order of germicidal action of acids at pH 5.5 was established: citric > acetic > lactic.

The amount of glucose required to provide a germicidal effect on staphylococcal strains can be reduced by 50% when used in combination with an acid taken at half the inhibitory concentration. The amount of salt can be reduced only by 30%, and sucrose by 20% to maintain the germicidal effect. The germicidal effect of food acids against diseases caused by the consumption of carbonated drinks was investigated. At a concentration of 0.02 N (the approximate strength of the solution used in drinks), the order of acid activity in destroying Escherichia coli at 30° was as follows: tartaric > glycolic > phosphoric > lactic > acetic > citric. Temperature coefficients for the rate of destruction of microorganisms varied depending on the type of acid; the order of their effectiveness at 30° was as follows: tartaric > phosphoric > lactic > citric acid, and at 0.6° phosphoric > lactic > tartaric > citric. The toxicity of a 0.02 N solution of lactic and citric acids increased with the addition of 10% sucrose or 2.5 volumes of carbon dioxide. In a study of the effect of acetic acid on spoilage yeast isolated from industrially produced sweet marinades, it was found that the addition of sugar or sodium benzoate reduced the amount of acetic acid required for canning. This paper provides a graph that can be used to determine, based on sugar and acid content, whether a given marinade is resistant to the growth of spoilage yeast.

When studying the fungistatic effects of fatty acids, it was found that within the pH range of 2-8, many of these acids were effective in preventing mold growth. Acetic acid was very effective at pH below 5.0, and the amount required to inhibit growth was lower the lower the pH value; at pH 2.0 less than 0.04 mol of acetic acid was sufficient, while at pH 5.0 a concentration of 0.08 to 0.12 mol was required. At the same pH, propionic acid was effective at lower concentrations than acetic acid and remained active up to pH 6.0-7.0.

Propionic acid and its salts have been widely recommended for preventing food spoilage, but its use is not permitted by UK food legislation. It was found that calcium propionic acid protects bread from the appearance of so-called ductility (stickiness). It has also been established that propionic acid prevents the surface growth of mold on butter. The acid is more active than its sodium salt. The influence of the pH of the environment is also important. It has been established that calcium propionic acid effectively protects fruit jelly, glazed jelly and similar products from mold growth.

In 1945, the fungistatic effect of sorbic acid was first noted; subsequent numerous studies confirmed the effectiveness of this acid in suppressing the growth of fungi. Studies of the effect of sorbic acid as a growth inhibitor for filmy yeast during the fermentation of cucumbers found that a 0.1% concentration of this acid completely inhibited the growth of molds and yeasts, without having a noticeable effect on the normal process of lactic acid fermentation. It was later discovered that 0.05% sorbic acid was sufficient to inhibit the growth of molds on cheese. Sorbic acid is also active when sprayed onto cheese wrappers. Sorbic acid is not currently a legal preservative, but recent studies have shown that it is less toxic than sodium benzoate.

Chemical preservatives

In sanitary legislation, the term “preservative” is defined as any substance that can prevent, slow down or stop the processes of fermentation, souring or other types of spoilage and rotting of food products. Substances such as salt, saltpeter, sugar, lactic and acetic acids, glycerin, alcohol, spices, essential oils and aromatic herbs are excluded from this heading. Many chemicals have a preservative effect due to the fact that, when combined with the protoplasm of a microorganism, they have a toxic effect on the cell. This action is not limited to the protoplasm of microbes, but applies to protoplasm in general, and substances that are toxic to microorganisms are usually harmful to body tissues.

For this reason, the addition of preservatives to foods is, with few exceptions, prohibited by UK law. The permitted preservatives in this country are: sulfur dioxide (including sulfites), benzoic acid (including its salts) and biphenyl (as applied to wrappers for imported citrus fruits). Sulfur dioxide and benzoic acid are allowed for use only in strictly controlled quantities in certain types of products. The use of nitrites in limited quantities is allowed for bacon, ham and cooked corned beef.

The effect of preservatives is largely determined by a number of factors, a detailed discussion of which is beyond the scope of this book. Below is a brief description that reveals their practical significance. The activity of a preservative mainly depends on its concentration. At sufficient concentrations, the effect of the preservative can be lethal to microorganisms. At lower concentrations, growth inhibition occurs, but not the death of microorganisms, and at very low concentrations the toxic effect is completely absent and the development of microorganisms can even be stimulated. The degree of dilution required to achieve these effects varies depending on the type of preservative; with the same degree of dilution of two different preservatives, their toxicity can be completely different. To determine the effect of the degree of dilution on the activity of the preservative, a numerical expression is used - the concentration coefficient.

Temperature turns out to be a very important factor in the activity of preservatives. In general, the toxicity of a preservative increases sharply with increasing temperature. The degree of increase in toxicity with a given increase in temperature is characterized by the temperature coefficient. Temperature affects not only the activity of the preservative, but also microorganisms. If the concentration of the preservative is sufficient only to inhibit the growth of the microorganism, then the stimulating effect of a slight increase in temperature may exceed the effect obtained by increasing the activity of the preservative. However, at temperatures above the maximum for microbial growth, very small amounts of the preservative can have a noticeably lethal effect.

Factors such as the type of microorganism and the amount present in the product should also be considered. As with other harmful effects, microbial spores are more resistant to the toxic effects of chemical preservatives than vegetative cells. It cannot be assumed that a given preservative can be equally effective against all types of microorganisms; even different strains of the same species exhibit different resistance to the same preservative. The number of cells present may influence the activity of the preservative; a concentration sufficient to control a minor infection may not be sufficient if a large number of microorganisms are present. In this regard, the need to protect canned products from even minimal contamination is absolutely clear.

In addition to these factors, the nature of the food product to which the preservative is added is very important. The concentration of hydrogen ions has a pronounced effect on the toxicity of most preservatives, which increases significantly in an acidic environment. Data have been published showing that the activity of benzoic, salicylic and sulfurous acids increases almost 100 times in strong acid compared to its neutral solution. Gillespie, working with B. fulva spores, found that at pH 3.0, about 0.001% sulfur dioxide was sufficient to prevent germination and inhibit spore viability, while at pH 5.0, 0.024% sulfur dioxide was required to achieve the same effect anhydride.

The degree of dissociation of weak acids, for example sulfurous and benzoic, is affected by the pH value of the solution; the lower the pH value, the higher the concentration of the undissociated fraction. The activity of the preservative is largely dependent on this concentration. In 1953, Shelhorn introduced the term absolute activity to determine the activity of the undissociated fraction. Comparison of the absolute activity of various preservatives shows that the activity of undissociated sulfurous acid is 100-500 times higher than the activity of undissociated benzoic acid towards the microorganisms studied by this researcher.

In the presence of organic substances, the effect of most preservatives is delayed. In some cases, a preservative may react with organic matter to form compounds that are inert or less toxic than the free preservative. Cruess found that sulfur dioxide combines with sugars and other components of fruit juice and that its bound form has a very low preservative effect, and at a concentration of 0.6% it is less toxic than at a concentration of 0.005% free sulfur dioxide. These data were later confirmed by Ingram, who came to the conclusion that the preservative effect of sulfur dioxide is carried out only by its free form (i.e., titrated with iodine).

Comprehensive information regarding the preservation of food products with chemical preservatives is provided in two works by English researchers.

Meat ambassador

Salting meat, in addition to giving it the desired color and taste, has a fairly significant preservative effect. The reactions that cause the formation of the characteristic red color of boiled corned beef involve the binding of the muscle tissue pigment myohemoglobin with nitric oxide to form the compound azooxymyoglobin (myoglobin with nitric oxide), which, when heated, turns into the persistent red pigment azooxymyochromogea. The source of nitric oxide is nitrite, which is present in the pickling solution or brine. Further details of the process are given in Jensen's work.

Typically, brine contains 20-28% salt and nitrate, sodium (sodium nitrate) about 1/10 of the weight of salt. It is practiced to introduce brine into meat by pumping it to speed up the process of salt diffusion into the meat. After pumping the brine, the meat is immersed in the brine, in which salt-resistant bacteria develop, converting nitrate into nitrite. Microorganisms of various types are present in the pickling brine; In order to suppress spoilage microorganisms, the salting process is carried out at a low temperature, approximately 5°.

A proposal has been put forward to directly add nitrite to the brine without first adding nitrate. However, subsequent studies have found that this method can lead to insufficient preservation, especially in relation to canned corned beef. In 1941, a review of earlier work on this issue was published, which found that nitrate present in meat retards the development of putrefactive bacteria, and 0.5% nitrate prevents the germination of Clostridium sporogenes supports, except in cases of heavy contamination. Experiments have shown that nitrate in concentrations usual for salted meat can cause a decrease in the heat resistance of putrefactive bacteria that cause spoilage. Emphasizing the importance of the presence of nitrate in salted meat, they indicate significant destruction of nitrite when the meat is heated as a result of reaction with proteins. Studies have been conducted to study the effect of pickling salts on the growth and heat resistance of Clostridium botulinum, which found that in meat agar, spore germination was reduced by more than 70% in the presence of 0.1% sodium nitrate, 0.005% sodium nitrite or 2% salt. Based on these data, it was concluded that the concentrations used in industrial practice can cause complete inhibition of bacterial growth. The same studies proved the presence of an obvious decrease in the thermal stability of Cl. botulinum when heating corned beef; however, this effect was attributed to the inhibitory effect of pickling salts. When heated corned beef was treated with a liquid culture medium such that a high dilution of inhibitory salts was obtained, the heat resistance of these microorganisms was not affected. However, in phosphate buffer with pH 7.0, salt, sodium nitrate and their mixture apparently caused a decrease in heat resistance at temperatures below 110°. Within the range of 110-112.7° no noticeable effect was detected.

A number of researchers have studied the effect of preservatives in meat on the heat resistance of putrefactive anaerobe and found that preservatives used in salting meat do not affect the heat treatment regime necessary for sterilizing meat. More recent work examined the effect of preservatives used in curing meat on the growth of the same microorganism in cooked meat; it was found that the main inhibitory factor was salt (at a concentration of 3.5 kg per 100 kg of meat). Sodium nitrate (78 g per 45 kg of meat) and sodium nitrite (7.1 g per 45.4 kg of meat) did not prevent meat spoilage, although sodium nitrite significantly slowed spore germination. Salt and sodium nitrate, salt and sodium nitrite, and a combination of these three preservatives were only slightly more active than salt alone. It is noted that some inconsistency in the conclusions regarding the inhibitory effect of preservatives used in salting meat may be due to fluctuations in the composition of the media in which these preservatives were tested.

In this regard, it should be noted that the pH value of the environment appears to have been insufficiently taken into account in some studies. It was found that at a concentration of 0.02% sodium nitrite had a pronounced inhibitory effect and in some cases completely inhibited the growth of microorganisms that cause spoilage of fish in an acidic environment (pH 6.0); at pH 7.0 this effect was completely negligible. Jensen, who in 1954 published an extensive review of the literature on the effect of preservatives used in salting on bacteria, pointed out that salted meat is acidic and that the inhibitory effect of nitrate, observed by many canned meat manufacturers over the years, was found in acidic environments .

Smoking

The process of smoking meat and fish is carried out after salting by keeping them in the smoke resulting from the slow combustion of wood sawdust. In general, the hardwood species preferred for this purpose are oak, ash and elm; soft resinous wood species are unsuitable for smoking, as they contain volatile substances that cause an unpleasant aftertaste in smoked meat or fish. The smoking process is carried out by hanging the product directly above smoldering wood or by generating smoke in a chamber and blowing it through pipes with blowers into the room in which the products to be smoked are located. To obtain high quality products, careful process control is required.

In addition to imparting the desired taste to the product, smoking has a pronounced preservative effect, partly due to the absorption of bactericidal substances contained in the smoke by the product. Research conducted in 1954 established that the preservative effect of smoking is created by aldehydes, phenols and aliphatic acids. During the smoking process, the surface layer of the product is impregnated with the indicated bactericidal smoke components, as a result of which most of the non-spore-forming bacteria die off. Subsequent microbial contamination of the product is reduced to some extent as a result of the residual preservative effect of the absorbed bactericidal substances; the presence of salt and the removal of water contained in the product, which occurs during the smoking process, also increase the shelf life of smoked products. The mycostatic effect of wood smoke components is not very pronounced, and smoked products are more susceptible to mold than bacterial spoilage. One study on fish smoking published in 1949 found that the pH of the surface layers dropped from 6.7 to about 5.9 during the smoking process. It is believed that the reason for this decrease was the absorption of acidic components of the smoke, which increased the sensitivity of microorganisms present on the fish to the action of bactericidal agents of the smoke.

A group of American researchers in 1954 studied the bactericidal effect of smoking on bacon. As a result, it was found that the temperature of the smoking chamber increases the bactericidal effect of smoke; fluctuations in relative humidity have little effect. The combined effect of thick smoke and high temperature (60°) reduced the number of bacteria present in the product by 100,000 times.

A review of works published in 1954 provides a complete summary of research into the chemical and bacteriological effects of the smoking process. Details regarding smoking methods are given in a paper published by Jones in 1942.

Preservation with spices

The preservative effect of some spices and herbs has been established for a long time, and there are indications that the activity of the essential oils of some spices is often higher than that of some chemical preservatives.

In all cases, the retarding or toxic effects of spices and herbs are attributed to essential oils. Most researchers come to the conclusion that cloves, cinnamon and mustard have a higher preservative effect than other spices and herbs. A review published in 1933 provides data on the effects of various spices, herbs and their essential oils on yeast (Saccharomyces cerevisiae). Black mustard powder has the strongest preservative effect; In second place are cloves and cinnamon. Cardamom, cumin, coriander, cumin, celery seeds, red pepper, nutmeg, ginger, marjoram and other spices and spices have very little or no preservative effect.

It was found that the volatile oil of mustard is a stronger preservative than the essential oils of other spices and herbs. Volatile mustard oil at a concentration of 0.02 or 0.5% in black mustard powder was more active compared to sulfur dioxide and benzoic acid taken at concentrations of 0.035 and 0.06% respectively. American researchers, using a number of bacteria as test organisms, have established the presence of significant fluctuations in the resistance of the same type of microorganism to the action of various spices. Their findings show that the only spices that had an inhibitory effect on bacteria, even in low concentrations, were ground cloves and cinnamon. Ground Jamaican pepper and cloves had an inhibitory effect at a concentration of 1%; mustard, nutmeg and ginger - in a concentration of 5%. A 50% emulsion of mustard essential oil at a concentration of 0.1% had a weak inhibitory effect, and at a 1% concentration it completely inhibited the growth of bacteria.

In 1943, research work was carried out to study the activity of a number of essential oils of spices and their components in relation to inhibiting the growth of surface microflora. Saccharomyces ellipsoides, S. cerevisiae, Mycoderma vini and Acetobacter aceti were used as test organisms. The data obtained revealed the presence of fluctuations in the resistance of these microorganisms to the action of spices. It was found that mustard essential oil had the most powerful termicidal effect; followed by cinnamon, Chinese cinnamon (cassia) and cloves. In first place in terms of toxicity of spice components was allyl isothiocyanate, carvacrol, followed by cinnamaldehyde and cinnamyl acetate (cinnamyl acetate), methyl ester of eugenol and eucalyptol, which had the same effect. The germicidal effect of spice essential oils was not related to surface tension. It is believed that the toxicity of spice essential oils develops due to chemical rather than physical factors.

More recent studies have found that, due to their higher concentration of active ingredient, spice essential oils are more effective than whole or ground spices in preventing the growth of yeast in laboratory media. Essential oils of cinnamon, mustard, cloves, Jamaican pepper, bay leaf, wintergreen (wintergreen) and mint at a concentration of 0.1% completely inhibited yeast growth in most cases. At concentrations above 1%, essential oils of mustard, cinnamon and cloves had a germicidal effect on yeast in essential oil - glucose agar media. When tested using plate-and-plate sowing, essential oils of Jamaican pepper, almond and bay leaf also showed a germicidal effect against yeast. Essential oils of anise, lemon and onion were classified as bacteriostatic substances. In 1953

Anderson et al. carried out work testing the effect of a number of essential oils on inhibiting the growth of microorganisms that cause food hang-up (bacteria and yeast) in glucose broth. The most active were the essential oils of mustard, garlic, onion and cinnamon. In acidified broth, the inhibitory effect on yeast development of most spice essential oils was increased; The exception was one yeast strain, which required a higher concentration of essential oil to inhibit its growth in the acidified broth than in the pH 7.2 broth.

The above and other studies show that the preservative effect of some spices may be of practical importance, but the concentrations used for this purpose are often limited by the taste properties of the product. In recent works, attention has been paid to studying the effect of essential oils of spices on the heat resistance of food microorganisms. This issue is also discussed in Chapter VIII.

Pickling

Vegetables used in the production of marinades are preserved by salting and fermentation, placing them in a saline solution with a concentration of 5-10% and subjecting them to spontaneous lactic acid fermentation. Salt reduces the activity of unwanted microorganisms, but does not prevent the growth of lactic acid bacteria and other types of microorganisms that convert the sugars contained in vegetables into lactic acid.

One report on the fermentation process of cucumbers notes the activity of yeast in this process. A later study found that most of the acidity of cucumber brine during fermentation is caused by the activity of Lactobacillus plantarum; other types of lactic acid bacteria, such as Leuoonostoe or gas-producing Lactobacillus species, contribute little to acid formation.

In addition to lactic acid, which is formed in a quantity sufficient for a preservative effect, alcohol, as well as acetic and propionic acids, are formed in small quantities. Fermentation proceeds best at a temperature of about 25° and normally ends in a few weeks; in this case, the vegetables should have a dense consistency and be transparent in appearance. The final acidity is about 1%. The fermentation process can be accelerated by using weak salt solutions (about 5%), which contribute to the rapid formation of high titratable acidity and low pH values ​​when pickling cucumbers. Increasing the salt content slows down acid formation; in this case, the overall acidity decreases and a brine with a higher pH value is obtained.

Rapid lactic acid fermentation is desirable to reduce the pH of the brine to a value that inhibits the growth of pectolytic microorganisms. If these microorganisms are allowed to grow in the early stages of the fermentation process, softening of the fruit tissue may occur. To prevent such softening, a certain amount of active brine is sometimes added to the fresh brine solution with cucumbers as a starter.

Research conducted in 1950 found that the softening of cucumbers in brine under industrial production conditions causes an enzyme similar to polygalacturonase; The same work describes a sensitive method for identifying enzymes that break down pectin in cucumber brine.

A recently published study on the softening of pickled cucumbers found that the predominant pectolytic microorganisms were Bacillus; they caused softening of cucumbers in cases where the normal fermentation process was delayed, as a result of which the pH value of the brine remained relatively high for several days.

At the end of the fermentation process, it is common practice to increase the salt content to at least 15% in order to promote shelf life. For successful storage it is necessary to prevent the growth of filmy fungi; these microorganisms oxidize the acid formed during fermentation (fermentation), and thus create favorable conditions for the growth of microorganisms that can cause softening and discoloration of vegetables.

The growth of surface microflora in vegetables fermented in barrels can be prevented by filling the barrels to the brim with brine. In fermentation vats installed under the roof, rapid foaming is observed, while in vats left in the open air, foaming usually does not occur due to the fact that the sun's rays retard the development of filmy microorganisms. This circumstance naturally led to the need to irradiate the fermented product using mercury lamps to prevent foaming on the surface of fermentation tanks installed indoors, and daily irradiation for 30 minutes turned out to be very effective. Other methods recommended to prevent foaming are: pouring the brine surface with liquid paraffin, using surface tension suppressors, and pouring the brine surface with emulsions of essential oils of spices, of which the emulsion of mustard essential oil turned out to be the most active. Detailed information about the fermentation of vegetables in the production of marinades is given in the work of Kruess.

Antibiotics

In recent years, many articles have appeared in the press regarding food preservation with antibiotics. These activities relate mainly to the preservation of raw food products or to the use of antibiotics as an additional measure in combination with reduced heat treatment of canned food. The latter method is discussed in more detail in Chapter VIII.

Many types of antibiotics have been tested for the preservation of raw foods, some of which have been found to have high bacteriostatic activity. As a result of the first research work in this area, carried out in 1946, the unsuitability of penicillin as a milk preservative was established. The possibility of using antibiotics for meat storage was also tested. The most active in preventing the growth of anaerobic microorganisms in meat stored at 20°C was a mixture of subtilin and streptomycin; streptomycin alone was ineffective.

The unsuitability of subtilin for preserving raw fish has been established. Quite good results were obtained using chloromycin at concentrations of 0.0025-0.005%, but aureomycin turned out to be the most active; even at a concentration of 0.001% it delayed microbial spoilage at 33-37° storage. At storage temperatures of fish and meat from 0 to 21°C, the most active antibiotics in preventing spoilage were aureomycin, terramycin and chloromycetin (in order of degree of activity). Aureomycin was distinguished by its pronounced property of delaying the spoilage of minced meat when used in concentrations from 0.00005 to 0.0002%, and its activity was the same when pieces of meat or fish were immersed in solutions containing 0.0005-0.001% of the antibiotic. Penicillin, gramycin, subtilin and other antibiotics either had weaker bacteriostatic properties or were completely ineffective.

Tarr and co-workers found that using ice containing 0.0001% aureomycin significantly increased the shelf life of fish. After storage in regular ice for 14 days, the bacteria count in fish was 190 million per gram, but in fish stored in ice treated with aureomycin, the bacteria count was only 20 million per gram. In clean sea water containing 0.0002% aureomycin, the fish was preserved longer than when stored in ice in the usual manner.

Studies have concluded that penicillin, bacitracin, and streptomycin do not prevent spoilage of raw ground beef; chloromycetin, aureomycin and terramycin increase the shelf life of this product by 2 times at 10°. Experiments using microorganisms isolated from meat have shown that the above three types of antibiotics are unequally active against different microorganisms. A method of introducing aureomycin into the circulatory system of a meat carcass was also tested; This method made it possible to prevent deep spoilage of meat due to a delay in transferring it to refrigerated storage.

The effect of antibiotics on microorganisms that cause food poisoning and food spoilage was also studied, using cream cake fillings as the material. The growth of the Staphylococcus aureus strain, which causes food poisoning, and natural heat-resistant microflora in these fillings was delayed for 2-3 days at 37°C by subtilin at a concentration of 0.01%. When Terramycin was combined at a concentration of 0.0001% with subtilin at a concentration of 0.011%, the preservative effect of antibiotics increased against both pathogenic (disease-causing) and non-pathogenic microorganisms. Aureomycin and terramycin in low concentrations (0.00006-0.0001%) inhibited the growth of Staphylococcus aureus, but were ineffective against microorganisms that cause food spoilage. Later experiments by the same researchers established the possibility of inhibiting the growth of Salmonella strains in cake fillings under the influence of subtilin with terramycin and a temperature of 37°.

The studies listed above and other studies show that some antibiotics have a clear bacteriostatic ability. However, the possibility of using them as preservatives is doubtful today. The studies carried out were of an experimental nature; For the industrial use of antibiotics as preservatives, further study is necessary. In addition to careful comprehensive identification of the activity of antibiotics as preservatives, it is also necessary to consider the possibility of their harmful physiological effects.

Ultraviolet irradiation

The lethal effects of ultraviolet rays on microorganisms have been studied for many years; An extensive literature has been created on this issue. In some cases, there is insufficient consistency in the results of laboratory experiments and the industrial application of this irradiation, which, apparently, is explained by the use of different radiation sources, different methods for determining the lethal effect, etc.

The penetrating power of ultraviolet rays is very low; the lethal effect is limited to microorganisms present on the surface or near the surface of the irradiated material, and the disinfection of the surrounding air is greatly limited by the presence of dust particles in it. In past work, the limited effect of ultraviolet rays in inhibiting the growth of microorganisms was not taken into account, and irradiation was used for purposes for which it was completely unsuitable. However, in recent years, more intelligent use of this type of radiation has shown that, under certain conditions, it is an effective means of preventing surface microbial contamination of food.

It is generally believed that the maximum germicidal effect is achieved at a wavelength of 2600 A. Low pressure mercury lamps have a high emissive power at a wavelength of 2537 A, very close to the maximum germicidal wavelength. The lethal effect varies depending on the duration of exposure and the intensity of the light rays, as well as on temperature, the concentration of hydrogen ions and the number of microorganisms per unit area of ​​exposure.

Relative air humidity affects the rate of death of bacteria suspended in the air, and this effect is more pronounced at relative humidity above 50%, when a further increase weakens the lethal effect. It has been established that bacterial spores are, as a rule, more resistant to ultraviolet radiation than vegetative forms; B. subtilis is 5-10 times more persistent than E. coli; molds and yeasts are more resistant to ultraviolet rays than vegetative forms of bacteria. However, these data do not entirely coincide with the data of other researchers, according to which the resistance of Mucor is 6 times, and Penicillium 5-15 times higher than that of bacteria; Yeasts, however, have the same or slightly higher persistence than bacteria. Molds can develop protective properties against ultraviolet rays using fatty or waxy secretions. Apparently, pigments also provide some protection: dark-colored spores are more resistant to radiation than uncolored species. In laboratory and field experiments, weak but long-lasting radiation covering one microorganism's life cycle was more effective than intense radiation over a short period. This phenomenon is explained by the fact that during certain stages of the life cycle the sensitivity of microorganisms to ultraviolet radiation increases.

There are many conflicting theories regarding the mechanism of action of ultraviolet radiation. These include the theory that there is an indirect lethal effect as a result of the formation of hydrogen peroxide and various chemical and physicochemical reactions in cell components. Currently, the formation of hydrogen peroxide is not considered to be the cause of the bactericidal effect of ultraviolet radiation, although this effect may also be associated with organic peroxides. It was shown that there is a very close similarity between the bactericidal curve and the absorption curve of certain substances in the cell nucleus, hence the conclusion was drawn that such substances participate in the mechanism of the lethal action of ultraviolet radiation. However, it is unknown what changes occur in the substance of the nucleus. This issue is addressed in an article published in 1954.

The use of ultraviolet rays in the food industry is in the following areas: tenderizing (softening) or ripening meat, aging cheese and sterilizing wrappers for the latter, preventing the growth of molds on the surface of baked goods, disinfecting air in food processing workshops and bottling drinks.

During storage, meat tissues soften as a result of the action of enzymes. This process occurs faster at relatively high temperatures, which, however, favor the growth of microflora on the surface of the meat. By preventing this growth with ultraviolet irradiation, the benefits of high temperature storage can be fully exploited. In this regard, mention is made of the use of “Sterilamps”, which produce radiation in the 2537 A zone, as well as in the 1850 A zone. Radiation at longer waves has a strong germicidal effect; at shorter wavelengths, atmospheric oxygen turns into ozone; irregularly shaped pieces and shaded areas of the irradiated surface are sterilized with ozone. In 1951, an extensive review of electromagnetic radiation and its application in the food industry was published; The review also covers ultraviolet radiation.

Disinfecting filtration

Mechanical removal of microorganisms by ultrafiltration, known as cold sterilization, is used in the production of fruit juices, beer and wine. This method, of course, can only be used to sterilize transparent liquid products. For this purpose, the Seitz disinfection filter (EK filter) is widely used. The product is first clarified and then passed through a special press, similar in design to a conventional filter press; The filter element consists of sheets or plates of a specially treated mixture of asbestos and cellulose. According to the researchers, the diameter of some filter holes is 17 u; Apparently, filters not only sift, but also retain microorganisms by adsorption. It is necessary to subject the filtered product to preliminary clarification, since otherwise the holes in the filter element will quickly become clogged.

Before use, the assembled filter press must be sterilized, for which it is purged for 10-20 minutes. steam under pressure. The sterile product leaving the press is placed under aseptic conditions in containers sterilized with steam or a solution of sulfur dioxide. The filter elements cannot be cleaned, so they are thrown away after use. For details on cold sterilization of fruit juices and similar products, please refer to the above article.

Chapter 3. Inactivation of foreign microflora and protection from spoilage of milk and dairy products

Biological principles of processing dairy raw materials

Milk is an excellent breeding ground for the development of microorganisms that cause spoilage of the product.

Methods for protecting food products from enzymes and microflora are based on three biological principles according to the classification of prof. Ya. Ya. Nikitinsky.

Biosis is the maintenance of vital functions in a product and the use of its natural capabilities. Bioz is not a preservation method in the usual sense. It comes down to implementing measures to ensure the short-term preservation of the product, in our case milk. These measures boil down to compliance with sanitary and hygienic conditions for obtaining microbiologically pure milk, which prolongs its preservation by increasing the duration of the bactericidal phase of milk, which prevents the development of microflora in it.

Milk preservation is based on two principles: abiosis and suspended animation. Conservation methods are based on mixed principles with one of them predominant.

Abiosis is the absence of life, that is, the complete cessation of all life processes in microorganisms.

To inactivate microorganisms and enzymes (abiosis), ultrasonic vibrations, ionizing radiation, antibiotics, chemicals and thermal effects can be used separately or jointly.

As a result, sterilization and death of vegetative and spore microflora occur.

Ultrasonic vibrations affect not only microflora and enzymes, but also milk components. Therefore, the use of ultrasonic treatment for milk preservation is carried out with the obligatory observance of optimal parameters that do not cause significant chemical, nutritional and taste changes in the product. However, the sensitivity of various bacteria to sound waves varies widely. This limits the use of ultrasound to inactivate microflora.

Currently, the dairy industry uses hydrodynamic vibrators operating in non-cavitation mode (at a pressure of no more than 0.3 MPa). They cause physiological changes in microorganisms, destroy their shells, and “loose” the elements of cellular structures.

For sterilization, ionizing radiation is used, which, depending on the wavelength, is divided into short-wave, ultraviolet and laser. Short-wave ionizing radiation (less than 10 nm) is characterized by high quantum energy; different microorganisms react to them differently. Ionizing radiation is used for canning if it is absorbed by milk.

Large doses of radiation are required to inactivate enzymes. The protein complex is most affected; calcium, magnesium and phosphorus are split off from it. At the same time, the viscosity increases significantly and the solubility of milk decreases.

Ionizing radiation can cause undesirable physicochemical changes in milk components, so it can only be used in combination with other types of sterilization. When milk is sterilized by UV radiation, the taste and smell of the milk deteriorate.

It is possible to use laser radiation for non-thermal sterilization of milk (S. F. Antonov and others). The thermal effect of high-frequency electromagnetic radiation also causes inactivation of microorganisms.

Food antibiotics are used in addition to the main method of canning. The most commonly used is nisin, which has no effect on mold and yeast and is antibiotically active against bacteria depending on the pH of the environment. It reduces the heat resistance of bacterial spores, thereby increasing the efficiency of heat sterilization, which makes it possible to soften sterilization regimes in the production of condensed sterilized milk. In our country, legislation allows the use of nisin.

Chemical sterilization of milk is limited because it causes spoilage. Only sorbic acid and its salts, which have a strong inhibitory effect on yeast and mold, are used in the dairy industry. They are tasteless and odorless and non-toxic to humans. In the body, sorbic acid is oxidized to form harmless substances.

In the dairy industry, sorbic acid and nisin are used together to inactivate a wide range of microflora. However, this combination is also used as an auxiliary means of sterilization.

Heat sterilization is most widely used in the dairy industry.

The production of condensed sterilized milk and cream is based on abiosis.

Anabiosis (from the Greek word - revival) is a state of a microorganism in which its life processes are so suppressed and slowed down that all visible manifestations of life are absent.

Microorganisms that are in a state of suspended animation, under favorable conditions, restore normal functioning.

The main reason for the onset of anabiosis is the loss of water by the protoplasm of the body's cells when exposed to high temperature, freezing, or an increase in the concentration of osmolytics in the environment.

Metabolism in any organism occurs only in the presence of water. Water is a medium in which nutrients are dissolved, used by the cell to obtain energy or for the synthesis of protoplasm. Water is also involved in many chemical reactions necessary for life processes. Decomposition products formed during metabolism are removed with water.

The principle of suspended animation is used to preserve milk and dairy products by cooling, freezing free water and increasing the osmotic pressure in the product.

This is based on reducing water activity to a level at which the development of microorganisms becomes impossible or significantly suppressed. At low temperatures, biological and biochemical processes slow down greatly. This is due to the known dependence of the rate of chemical reactions on temperature, as well as the state of the cytoplasm, the carrier of the vital functions of the cell. Under the influence of cold, the permeability of protoplasm decreases. As a result, the metabolism slows down, the supply of oxygen into the cell from the outside through the narrowed pores of the protoplasmic membrane decreases, the mass exchange between the cell and the environment decreases, the activity of enzymes decreases - the life of the cell freezes, without stopping at all, the cell falls into a state of suspended animation.

When warmed up, biological and biochemical processes in the microbial cell are restored, and the cell comes to life.

Cooling milk and dairy products to low positive temperatures of 1-5 °C sharply reduces the development of microbes, especially lactic acid microbes, significantly prolonging the bactericidal phase of milk and the duration of its storage.

Organisms after suspended animation are able to revive if they retain at least 1/4 of the water, when there is no complete freezing, and when tissue fluids remain at low temperatures in a supercooled liquid state. Ice crystals cause irreversible changes in the body's cells. Rapid cooling to temperatures of -90 ... -160 ° C leads to the production of a glass-like form of water, which does not destroy the cell, which is capable of revitalization.

During freezing, as the temperature of the product decreases, the water molecules come closer together, the forces of their mutual attraction increase, and the Brownian motion weakens. When the energy of water molecules falls below the level of their constant orientation, crystal formation begins with the release of a crystallization heat of 335 kJ mol 1. At the same time, the product’s resistance to microbial spoilage increases. According to Scott, water activity and in is defined as the ratio of the vapor pressure over an aqueous solution to the vapor pressure of pure water at the same temperature:

a =P Po- 1

where p is the vapor pressure above the aqueous solution , Pa; p 0 - vapor pressure of pure water, Pa.

Water activity is the main factor in regulating the relationship of microorganisms with water. The minimum moisture required for the life of microorganisms and the corresponding water activity for bacteria is 20-30% at and in not lower than 0.94-0.9, yeast and molds - 11-13% at and in not lower than 0.88-0.8. Some organisms reproduce at water activity levels close to 0.73. It can be assumed that with water activity less than 0.7, food products are preserved for a long time.