In food products, microorganisms can cause changes:
colors - yellowish, greenish, pink, gray and other spots appear on dairy products, egg whites, fish, meat;
consistency - softening of products under the action of microbial enzymes on organic substances of food products - proteins, gelatin, collagen, etc.;
odor - the acquisition of an unusual odor, often unpleasant, caused by decomposition and rotting.
Food spoilage is caused by microbes with a heterotrophic type of nutrition - saprophytes, which use ready-made organic substances of products: proteins, carbohydrates, fats, vitamins. Microbes break down these complex substances with the help of enzymes, the activity of which depends on pH. Depending on the active acidity of products, microorganisms affect them differently. Therefore, microbial spoilage of food products depends both on the properties of microorganisms and on the environment in which they are located.
The presence of water in food also promotes the development of microorganisms.
The proliferation of microorganisms can lead to the loss of the original properties of food products, making them unsuitable for use. Even in the absence of reproduction, prolonged presence of microbial cells or their enzymes in food causes a change in its quality.
The main microorganisms that cause spoilage of food products are gram-negative bacteria.
Yeasts and molds also play a certain role in this.
Numerous groups of microorganisms can grow in food products. Since 1982, the CMEA member countries have approved a List of microorganisms, the presence of which must be checked in each type of food product to ensure their quality and sanitary safety. Bacteria are the most important. The following are subject to verification:
Mesophilic bacteria
Thermophilic bacteria
Psychrophilic bacteria
Coli bacteria and E. coli
Pathogenic bacteria - causative agents of gastrointestinal diseases
Microorganisms that cause food poisoning
Osmophilic microorganisms
Proteolytic microorganisms
Salt-loving microorganisms
Microorganisms that break down pectin
Acid-forming microorganisms
Molds
Spore-forming bacteria (aerobes and anaerobes)
As can be seen from the above list, microorganisms with different morphological and physiological properties and biochemical abilities can multiply in food products.
Characteristics of some of them are given in this section (mesophilic and psychrophilic bacteria, spore-forming aerobic and anaerobic microorganisms) and other sections (coli bacteria and E. coli, as well as causative agents of infectious diseases and food poisoning, microorganisms that are pests in various sectors of the food industry).
Food products can contain a variety of microflora. The natural and harmless microflora of food products is a complex biocenosis, which serves as a biological defense against unwanted microorganisms. However, certain types of microorganisms can affect the quality of food products. If the processing, storage or sale of products is violated, these microorganisms can multiply to a significant level and lead to product spoilage and food poisoning.
Microbial spoilage of products can occur through fermentation, rotting, molding and decomposition of fats. Milk, cheeses and other dairy products undergo butyric acid fermentation due to the proliferation of spore-forming anaerobic bacteria in them. When this happens, butyric acid is formed and there will be an unpleasant taste and smell. Acetic acid fermentation leads to sour wine and beer. Alcoholic fermentation, caused by yeast, is used in the production of alcohol, beer, etc. Lactic acid fermentation is used to prepare various fermented milk products.
Putrefaction is the process of decomposition of proteins with the formation of foul-smelling gases, caused by the action of a complex of putrefaction microbes, and is the cause of spoilage of many protein products. Molds cause molding of products when stored in refrigerators, since fungi are resistant to low temperatures.
Of particular danger is the infection of food products by pathogenic microorganisms, many of which are capable of not only maintaining viability in products for a long time, but also intensively multiplying in them.
Microflora of dietary fats
There are natural fats of animal and vegetable origin and industrially produced fatty products (margarine, mayonnaise). Rendered animal fats and vegetable oils contain a very small amount of moisture and will be an unfavorable environment for most microbes.
Butter contains a lot of moisture, microbes develop both on the surface of the butter and inside it. Putrefactive and other bacteria, yeast, multiplying on the surface of the oil, decompose proteins and fats, leading to the formation of staff (a bright yellow layer). When storing oil for a long time, mold fungi develop on the surface (podium, mucor, etc.). Rancidity of the oil is caused by fat-splitting bacteria, The bitter taste is also imparted by the products of protein breakdown by proteolytic bacteria and micrococci.
Microflora of eggs and egg products
Egg - an excellent environment for the proliferation of microorganisms. When storage temperature fluctuates, eggs experience “thermal” respiration. An increase in temperature causes the contents of the egg to expand and force air out of the path (air chamber) through the burrows and out. As the temperature drops, air is drawn into the egg. Along with the air, mold and various spores penetrate into the egg, incl. pathogenic microorganisms, Escherichia coli, Proteus coli and other putrefactive bacteria, which are deposited on the subshell membrane, which keeps them from penetrating the protein.
Eggs obtained from a sick bird become infected endogenously, that is, the infection enters the contents of the egg before the shell is formed. It is possible for pathogenic microorganisms to enter the egg exogenously (from the outside) through damage to the shell. The white of a fresh egg contains microbes, incl. salmonella do not survive due to the bactericidal effect of lysozyme.
The presence of Salmonella is most often found in waterfowl eggs. In adult ducks and geese, salmonellosis is asymptomatic, but when infected, the shell and yolk of eggs become infected with salmonella.
Mold spores usually develop on the surface of the egg shell, forming colonies of various sizes, which look like spots during ovoscopy or cover the egg completely (“cuff”) Mold gives the egg an unpleasant moldy smell, making it unsuitable for food.
During storage, the protective properties of lysozyme are reduced, and microbes penetrate inside the egg. The proliferation of putrefactive microflora causes decay processes with the formation of breakdown products of egg proteins, incl. and toxic, with an unpleasant taste and odor - ammonia, hydrogen sulfide, etc. This type of egg spoilage is called “putrefactive decomposition”. The use of eggs with this defect is not permitted.
Egg powder may contain an increased number of different microorganisms, incl. Proteus and Escherichia coli. There is a high probability of salmonella entering it, therefore egg powder must be subjected to reliable heat treatment. Due to the increased risk of salmonellosis, melange (a mixture of white and yolk) is frozen and not used in public catering.
Microflora of canned food
The safety criteria for canned food products will be the absence of microorganisms and microbial toxins that cause food poisoning. The most dangerous food poisoning associated with the consumption of canned food will be botulism and toxic infection caused by the perfringens bacillus. Botulinum bacillus and perfringens bacillus are related to spore-forming anaerobic mesophilic bacteria from the group of sulfite-reducing clostridia. Spores of clostridia and other gas-forming bacteria are able to withstand high temperatures during canning and multiply in canned food in the absence of oxygen with the formation of carbon dioxide and hydrogen, causing swelling of the jars (bombing). In canned food with high acidity (pH below 4.2), clostridia spores do not germinate and do not multiply.
Canned vegetables and meat and vegetables can be subject to flat acid spoilage - souring of the product without swelling of the can. This type of spoilage is caused by thermophilic aerobic and facultative anaerobic acid-forming bacilli.
In case of heavy infection of raw materials and insufficient sterilization in canned and semi-canned food (pasteurized, etc.), non-spore-forming microorganisms - cola and molds, molds, yeast, Staphylococcus aureus, etc. - may remain viable.
S. aureus is a non-gas-forming microorganism, the reproduction of which in canned food is not accompanied by bombing. In these cases, canned food can cause staphylococcal toxicosis and other food poisoning. The proliferation of staphylococci and the accumulation of enterotoxin is stopped at low pH values in canned food.
Microflora of grain products and bread
Microorganisms (bacteria, mold spores, yeast, etc.) enter the grain from the soil and with dust. The microflora of cereals and flour is determined by the microbial composition of the grain. 1 g of grain products can contain from several thousand to a million microbes.
Of epidemiological significance is the damage to grain by mold fungi that are dangerous to humans - ergot, fungi of the genus Fusarium and Asprgillus.
Ergots and molds from the genus Fusarium and Aspergillus are capable of releasing mycotoxins into grain, causing severe food poisoning - mycotoxicosis. Mycotoxins can have carcinogenic and other dangerous effects on humans in very small quantities; they are not destroyed in products during heat treatment.
Flour is less resistant to microbial spoilage than grains and cereals. If storage conditions are violated, when moistened, the acidity of the flour may increase due to the proliferation of lactic acid bacteria, the proliferation of mold fungi and, as a result, the appearance of an unpleasant taste, smell or lumpiness of the flour.
When baking bread, most microorganisms die, but the spores remain viable.
Wheat bread can be affected by “stringy (potato) disease.” Reproduction of the causative agent of the bread disease Do not forget that you. subtilis is promoted by low acidity, characteristic of wheat bread.
When cooling bread or storing it in bulk in conditions of high temperature and humidity, spores should not be forgotten that you. subtilis germinate and break down bread starch into dextrins with their enzymes. The crumb first acquires an unpleasant smell of overripe melon or valerian, becomes sticky, then darkens and becomes viscous. Bread affected by “potato disease” is unsuitable for food purposes.
Bread molding is caused by the development of fungi Peniciilium glaucum (green mold), Aspergillus glaucum (white mold), Mucor macedo (capitate mold), the spores of which fall on the bread from the air after baking the bread.
Microflora of vegetables, fruits and berries
On the surface of fresh vegetables and fruits there are a large number of different microorganisms that get there from soil, water and air. The presence of peel, phytoncides, essential oils and organic acids prevents the development of microbes that cause spoilage of fruits and vegetables. Lingonberries and cranberries are particularly resistant to spoilage due to their benzoic and sorbic acid content.
When the skin of fruits and vegetables is damaged, spoilage microbes multiply on the surface and enter the pulp. The processes of microbial spoilage are facilitated by overripening and long-term storage of fruits and vegetables. Rot and other spoilage of vegetables and fruits are caused by molds (late blight and dry rot of potatoes, black cancer of apples and pears, etc.), bacteria (wet rot of potatoes, black spot of tomatoes), yeast (spoilage of berries) Certain types of fungi from the genus Penicillium, breeding on apples, tomatoes, and sea buckthorn berries, they are capable of secreting the mycotoxin patulin, which has a pronounced carcinogenic and mutagenic effect.
As a result of eating raw vegetables, fruits and berries contaminated with soil, dysentery, typhoid fever, cholera and other intestinal infections can occur. Familial outbreaks of dysentery due to consumption of strawberries are known. The survival time of pathogenic microorganisms and helminth eggs on the surface of vegetables and fruits can significantly exceed their shelf life before sale. Eating vegetables, fruits and berries without heat treatment can lead not only to intestinal infections, but also to yersiniosis, geohelminthiasis, amoebic dysentery, etc.
Vegetables can become infected with Yersinia bacilli from rodents or from contaminated soil or water. During long-term storage in vegetable stores, Yersinia multiplies on the surface of vegetables and accumulates in significant quantities, sufficient to cause human disease. Most often, the cause of ieriosis is the consumption of salads made from raw vegetables from the old harvest in spring or early summer.
Many food products are a favorable environment not only for preservation, but also for the proliferation of microorganisms.
All microflora of food products are conventionally divided into specific and nonspecific.
Specific microflora include strains of microorganisms used in the process of technological food production (lactic acid products, bread products, beer, wine, etc.).
Nonspecific microflora refers to random microflora that enters food products during their procurement, delivery, processing and storage. The source of these microbes can be raw materials, air, water, equipment, animals, or humans.
Infection of food products with microorganisms can lead to foodborne illnesses and other diseases in people.
Microbiological food safety criteria are divided into four groups:
Sanitary indicator microorganisms: coliforms, taking into account bacteria of the genus Escherichia, Klebsiella, Citrobacter, Enterobacter, Serratia.
Potentially pathogenic microorganisms: coagulase-positive staphylococci, bacteria of the genus Proteus, sulfite-reducing clostridia, B.cereus.
Pathogenic microorganisms, including salmonella.
Microorganisms are indicators of the microbiological stability of the product (yeast, mold fungi).
Sanitary and bacteriological examination of food products
Sampling. Sampling is carried out sterilely, using sterile devices, in sterile containers. Samples are placed in appropriate containers and sealed. Transportation is carried out in cooler bags as quickly as possible.
Sanitary microbiological assessment of food products includes determination of the total microbial number and titer of sanitary indicative microorganisms.
Determination of total microbial count (TMC)
TMC is the total number of microorganisms contained in 1 g (cm 3) of the product. To determine it, the multiple dilution method is used.
Multiple dilution method. When studying dense substrates, the sample is crushed in a homogenizer or ground in a mortar with quartz sand and the initial suspension is prepared at a dilution of 1:10. From the resulting suspension or initial liquid material, a series of subsequent dilutions are prepared in such a way that when the last two dilutions are sown on a Petri dish, from 50 to 300 colonies grow in agar. From the last two dilutions, 1 cm 3 is added to a cup and 10-15 ml of melted and cooled to 45 0 C MPA is poured. The dishes are incubated at 37 0 C for 48 hours, the number of grown colonies is counted. TMC is determined taking into account the dilution of the test material.
Limiting dilution method (titer). A series of tenfold dilutions are prepared from the starting liquid material until the presence of one bacterial cell can be assumed in the last test tube. Inoculation is done in a liquid selective medium, followed by the isolation of microorganisms on a solid nutrient medium and the study of their characteristics.
The titer is taken to be the smallest amount of substrate in which one individual of the desired microorganism is found.
Determination of sanitary indicator microorganisms
Sanitary indicator microorganisms characterize the product from the point of view of epidemic danger.
Coliform bacteria are considered the main sanitary indicator microorganisms and methods for determining quantity and titer are used for quantitative accounting. In this case, quantity is understood as the determination of the most probable number (MPN) of coliforms per unit mass or volume of the product.
Determination of NHF coliforms.
To determine NSP from a liquid product or an initial solid suspension, dilutions of 10 -1, 10 -2, 10 -3 are made successively, of which 1 cm 3 is inoculated into three test tubes with Kessler medium for each dilution. After 24 hours of incubation at 37 0 C, changes in the color of the medium and gas formation are recorded in the test tubes. Depending on the number of germinated test tubes, the NPs of coliform bacteria are determined.
Determination of coliform titer
Tenfold dilutions of the analyzed material are prepared and sown on Kessler's medium to identify the smallest amount of product in which E. coli is present. The inoculations are thermostated at 43 0 C for 18-24 hours. Each test tube is inoculated onto Petri dishes with Endo medium so as to obtain the growth of individual colonies. The crops are incubated at 37 0 C for 18-24 hours, after which smears are made from the grown colonies and stained with Gram. If gram-negative rods are detected in smears, the colonies are subcultured on Hiss media with glucose. The presence of gas formation in test tubes with cultures indicates the presence of coliform bacteria.
The titer is determined by the smallest amount of product in which coliform bacteria are found or by standard tables.
When assessing food products based on microbiological indicators, it is necessary to take into account the possibility of detecting pathogenic and opportunistic microorganisms. Food products are analyzed for the presence of salmonella, sulfite-reducing clostridia, staphylococci, and proteus. In a broader study, products are examined for fungal flora.
To test for salmonella, a suspension is prepared from the analyzed products and inoculated on accumulation media (selenite, magnesium chloride broths). After daily incubation at 37 0 C, subculture is carried out on Endo, Levin, Ploskirev media or bismuth sulfite agar. Next, colonies are identified by taking into account the growth characteristics on Hiss, Ressel, Olkenitsky media and in an agglutination reaction with monoreceptor sera.
To identify sulfite-reducing clostridia, the test material is inoculated into 2 test tubes with Kitt-Tarozzi, Wilson-Blair or casein-mushroom medium. One test tube is heated at 80 0 C to destroy the accompanying microflora. The crops are incubated at 37 0 C for 5 days. If there is characteristic growth, it is enough to identify specific microflora in the smears and, if necessary, check for toxin formation in a bioassay on white mice.
To identify staphylococci, the test material is inoculated on yolk-salt agar. The crops are incubated in a thermostat for 24 hours. Colonies suspicious for staphylococci are stained with Gram, they are subcultured on milk agar and further identification of the isolated culture is carried out.
To identify Proteus, the test material is inoculated onto agar slants using the Shukevich method. After daily incubation, smears are made from the upper edge of the growth and, if there are gram-negative polymorphic bacteria in them, a conclusion is made about the isolation of Proteus; if necessary, biochemical and antigenic typing is used.
Table of contents of the topic "Sanitary and bacteriological research.":Nonspecific microflora of food products. Sanitary and microbiological analysis of food quality.
Nonspecific microflora of food products accidentally falling on food products from the environment. It consists of saprophytes, pathogenic and opportunistic microorganisms, as well as species that cause food spoilage. Many food products contain abundant saprophytic microflora, causing the formation of various biocenotic relationships.
Presence of some saprophytes promotes the development of biochemical processes that are natural to the food product, on which its quality and often safety depend on as a result of antagonistic resistance to pathogenic bacteria that enter the products. The degree of contamination by foreign microflora depends on many factors: the correct preparation of the food product itself, its transportation, storage, subsequent processing technology and, at all stages, compliance with the sanitary regime.
Most often studied two main indicators- presence, as well as the degree of contamination of products with microorganisms and the presence of pathogenic microorganisms. Detection of pathogens is certainly more accurate, but also more labor-intensive, so it is used only during primary meat processing, as well as when conducting some analyzes of milk, meat products and monitoring canning production. The study has three objectives.
1. Raw material quality control, used in the production of food products and assessment of the sanitary and hygienic conditions of their production.
2. Control of food storage modes and assessment of the sanitary and hygienic conditions of their transportation and sale.
3. Control over ensuring epidemic food safety.
When conducting research they use qualitative and quantitative methods. Qualitative methods are used to determine the nature of technological microflora and pathogens of food spoilage. Quantitative methods in combination with other indicators determine the shelf life and sale of products. The total number of microorganisms is examined in 1 g or 1 cm3 of product using the method of multiple dilutions. Specific species are determined using specific tests.
Microbiological indicators for milk and dairy productsIt should be remembered that on nature of microbial contamination influence the physicochemical properties of products. Most microorganisms do not survive well in foods with very low and high pH values. They multiply especially abundantly in products with liquid and semi-liquid consistency. In dense, especially dry or powdery products, the conditions for the proliferation of microbes are difficult and they are located in “nests*”. The contamination of food products is influenced by certain features of the technology of their production and storage.
Mechanical recycling(production of minced meat, puree, etc.) increases the likelihood of contamination and promotes the homogeneous distribution of microorganisms throughout the product.
Chemical treatment(salting, pickling) contributes to a sharp decrease in the number of microorganisms. Often, salted products are additionally smoked, which further reduces contamination.
The growth of microorganisms is significantly affected temperature regime of their production and storage. An increase in temperature has a more unfavorable effect on microbes than a decrease, which is why high temperatures are widely used for food processing.
Hygienic standards for microbiological indicators include control over 4 groups of microorganisms.
SPM, which include mesophilic aerobic and facultative anaerobic microorganisms - MAFAM (producing growth after incubation at 30 °C for 72 hours using the deep sowing method) and coliforms.
Opportunistic microorganisms, which include E. coll, Staphylococcus aureus, Bacillus cereus, Proteus and sulfite-reducing clostridia.
Pathogenic microorganisms, primarily salmonella.
Microorganisms, causing food spoilage, primarily yeast and molds.
For different groups food raw materials and food products There are specific GOSTs for these products. In the absence of GOSTs, hygienic requirements for the quality and safety of food raw materials and food products are used. Regulation in terms of microbiological quality and safety of food raw materials and food products for most groups of microorganisms is carried out according to an alternative principle, that is, they normalize the mass of the product, which is not allowed to contain coliform bacteria, most opportunistic microorganisms, as well as pathogenic microorganisms, including salmonella. In other cases, the standard reflects the permissible number of CFU in 1 g (ml) of the product.
Of particular importance is sanitary and bacteriological control over the production of canned food. Canned food - food products packaged in hermetically sealed containers and preserved by heat treatment or combined methods. Canning production aims to create food products that retain high nutritional properties for a long time and at the same time are safe for the health of the consumer. Food products prepared for the production of canned food contain microorganisms of a wide variety of species composition and quantity, originating from the microflora of raw materials and various sources. Regime heat sterilization kills microorganisms in the canned product, and hermetically sealed jars prevent the penetration of microorganisms inside. In most cases, canned food is made from products of varying quality, and in almost every batch of canned food, some of the cans turn out to be unsterile. This is due to the fact that among the many microorganisms, taking into account the heat resistance of which the sterilization regime is established, there are also more heat-resistant species. They are the residual microflora of canned food. If non-spore-forming microorganisms are not resistant to heat, then the spores of meso- and thermophilic bacilli and clostridia are particularly resistant to high temperatures (from 115 to 130 ° C). Compliance with the specified storage conditions for canned food prevents the development of residual microflora weakened after sterilization, and the canned food remains of good quality (in this case they are called industrial sterile).
Among the residual microflora of canned food The most commonly found are the following.
Mesophilic bacilli: Bacillus subtilis group (I subtilis, B. pumilus, B. licheniformis), Bacillus cereus group (B. cereus, B. anthracis, B. megaterium, B. thuringiensis); Bacillus polymixa group (B. polymixa, B. macerans, B. circulans).
Bacteria genus Lactobacillus.
Clostridia.
Yeast.
Molds.
Depending depending on the heat treatment mode and pH values, canned products are divided into groups: A, B, C, D, E. This division allows microbiological research to be carried out in a certain direction. Depending on the purpose, groups of canned foods are examined for:
industrial sterility,
causative agents of spoilage of canned food,
pathogenic microflora according to epidemiological indications.
1). MEAT. In the first hours after slaughter, the deep layers of meat are practically sterile. On the surface of the carcass the species composition of microflora is diverse - this soil bacteria(cocci, bacilli, clostridia), intestinal bacteria, and mold fungi. By multiplying and accumulating on the surface of the carcass, they gradually penetrate into the thickness of the meat and cause spoilage processes.
When storing meat in cooling chambers, the microflora remains unchanged for some time as a result of the formation of a dried layer on the surface of the carcass, which prevents the development of microorganisms. Subsequently, the microflora undergoes qualitative changes: mesophiles die off and psychrophiles develop, where rod-shaped bacteria become the predominant species, capable of reproducing at a temperature of 0 ¸ –5 0 C, and some species even at –8 ¸ –9 0 C. In aerobic (in the presence of oxygen air) storage conditions of chilled meat, these bacteria are the main causative agent of its spoilage. First, individual colonies grow on the moister surfaces of the product, then a continuous mucous coating of gray, greenish or brown color forms, and the smell and taste of the meat changes.
Molds are the main causative agents of meat spoilage when stored at temperatures of –4 ¸ –9 0 C. These fungi not only change the appearance and smell of the product, but also cause deep breakdown of proteins. Due to the active breakdown of lipids, the product goes rancid. At some subzero temperatures, molds grow even on frozen meat.
2) BIRD. A feature of the microflora of poultry meat is the possibility of the presence of bacteria from the Salmonella group in it, which can cause foodborne toxic infections. In this regard, waterfowl carcasses are especially dangerous.
3) FISH. The microflora of fish is presented spore and non-spore bacilli, micrococci, sarcina, as well as water-dwelling molds and yeasts. As a result of storing fish at low temperatures, mesophilic forms of bacteria die off, and psychrophiles develop. Fish from northern seas and rivers are more contaminated with psychrophiles, molds and yeasts. With a sharp drop in temperature, the growth of bacteria stops, and even psychrophiles begin to multiply only after some time. If at 18 0 C the number of bacteria reaches 10 8 – 10 9 per 1 g of fish during the day, then at a temperature of 0 ¸ –2 0 C growth is observed only on the fourth – fifth day.
Ice, seawater and brine can be sources of microorganisms. In frozen live or very fresh fish, microorganisms develop on the surface. They are absent in the thickness of the muscles.
4) MILK AND CREAM. Here, microorganisms multiply faster than on the surface of solid products. As a result of infection, raw milk may contain various microflora: lactic acid bacteria, spore and non-spore bacilli, coliform bacteria, micrococci and staphylococci.
The development of milk microflora occurs in several phases. Bactericidal phase characterized by the fact that after milking cows, microorganisms in the milk do not develop and even partially die as a result of the action of special substances. Immediate cooling of milk after milking can extend the bactericidal phase to 24 - 28 hours. Development phase of mixed microflora characterized by the development of microorganisms that get into milk. Depending on the storage temperature, thermomeso- or psychrophiles begin to predominate in milk. Developmental phase of lactic acid bacteria characterized by a rapid increase in acidity as a result of the fermentation of lactose into lactic acid. If the environment in milk is alkaline, then conditions will be created for the development putrefactive and butyric acid bacteria and the milk will become unfit for consumption.
If milk and cream are stored at low temperatures, the growth of lactic acid bacteria is delayed. Under their influence, during relatively long-term storage of milk, proteins and fats are broken down with the formation of bitter and unpleasant-smelling products. Sometimes when milk is stored refrigerated, mucus may appear, most often caused by psychrophiles.
Fruits and vegetables can be a source of pathogenic and toxic microflora. Particularly common are pathogens of intestinal diseases that do not die off completely during long-term storage. Products containing few organic acids can be affected by both molds and bacteria.
When storing frozen fruits, vegetables and berries, the bacteria gradually die off. First of all, non-spore bacilli die, including bacteria of the intestinal group; micrococci, staphylococci and spore bacteria are more resistant. When these products thaw, they begin to multiply rapidly, leading to product spoilage.
In addition, products of plant origin contain phytoncides of varying activity. Vegetables such as onions, garlic and horseradish emit bactericidal substances that kill disenteric bacteria, E. coli, staphylococci, and vibrios. Phytoncides from the peel and pulp of citrus fruits, bananas, pomegranates and apples, as well as berries, have a detrimental effect on various bacteria and molds.
