Studies of indicators of the assortment and quality of drinking milk. Defects in milk and dairy products Defects in raw milk and factors causing them

In appearance and consistency, milk should be a homogeneous liquid without sediment, baked milk and high fat content - without cream sludge. The smell and taste must be clean, without extraneous flavors and odors not characteristic of fresh milk; for baked milk - a well-pronounced aftertaste of high pasteurization; color - white, with a slightly yellowish tint, for melted - with creamy, for low-fat - with slightly bluish tints.

The assessment of the smell and taste of milk is carried out by a commission consisting of at least three experts, specially trained and certified. Smell and taste are determined both immediately after sampling and after their storage and transportation for no more than 4 hours at a temperature of 4 ± 2 °C. The analyzed samples are compared with a pre-selected sample of milk without odor and taste defects, which received a score of 5 points. The results of the evaluation of this sample are not included in the processing.

Immediately after opening the flask, determine the smell of milk. Then milk (20 ± 2 cm 3) is poured into a dry, clean glass beaker and the taste is assessed.

The assessment is carried out on a five-point scale in accordance with the following characteristics of smell and taste

Based on the score, an expert sheet is drawn up:

If the discrepancy in the assessment by individual experts exceeds one point, the assessment of the sample should be repeated no earlier than 30 minutes later. The final result of the test is taken as the arithmetic mean of the results of the marks awarded by the experts. The result is rounded up to an integer. Milk with a score of 5-4 points is classified as the highest, first or second grade, depending on other indicators. Milk with a score of 3 points is classified as second grade in the winter-spring period of the year, and as non-grade milk in other periods of the year.

Physical and chemical indicators should correspond to those given in table. 1 with a degree of purity according to the standard of mechanical contamination not lower than the 1st group.

Table 1. Physical and chemical parameters of milk

According to bacteriological indicators, pasteurized milk in bottles and bags must comply with the requirements of group A with a total number of bacteria in 1 ml of milk not more than 75 000 and a titer of E. coli 3 ml and group B, respectively, 150 000 and 0.3 ml, and pasteurized in flasks and tanks - 300 OOO and 0.3 ml (see GOST R 520 90-2003).

There are slightly different requirements for harvested milk. In taste and smell, a pronounced fodder taste is allowed; cleanliness should not be lower than the 2nd group according to the standard of mechanical contamination.

The names of milk and products of its processing must comply with the concepts established by Article 4 of the Federal Law of June 12, 2008 No. 88-FZ "Technical Regulations for Milk and Dairy Products".

Milk vices

Milk vices are caused by the poor quality of the feed, the ingress of microflora into the milk, improper processing technology, violation of the conditions and terms of storage, and other reasons.

Consistency defects caused by the activity of certain microorganisms. Milk acquires a thick consistency with the participation of lactic acid bacteria, mucous or viscous - under the action of mucus-forming bacteria. As a result of the development of E. coli bacteria, milk undergoes fermentation and foam is formed. When rennet-producing bacteria enter, the milk coagulates during heating even at low acidity.

Smell vices most often due to specific odors of feed or unsanitary conditions of the premises in which animals are kept. Smell defects include barnyard, rotten, cheesy, garlic, etc.

Defects of taste- the most common type of defects:

• milk acquires a sour taste as a result of the vital activity of lactic acid bacteria or E. coli;
• rancid taste is formed in milk during its long-term storage at low temperatures under the action of lipase enzymes, and also appears in the milk of the last days of lactation;
• bitter taste is due to the activity of putrefactive peptonic bacteria in milk, can be caused by the presence of wormwood in feed;
• unpleasant specific flavors can appear from the presence in the diet of animals of nettle, garlic, onion, turnip, radish, field mustard, etc .;
• salty taste appears in some diseases of the udder;
• milk acquires a metallic taste as a result of the interaction of lactic acid with the metal of the container;
• a greasy taste occurs when milk is stored in the light as a result of the oxidation of milk fat by atmospheric oxygen;
• smoky taste and smell are possible in sterilized milk and packages if the paper is burned when gluing the transverse seams of the package.

color flaws(redness, blue and yellowing) appear under the influence of pigmenting bacteria. Sometimes the yellowing of milk is associated with the ingress of blood into the milk during milking due to the diseased state of the animal.

When milk freezes, its quality noticeably decreases: the colloidal state is disturbed, as a result of which the milk is stratified; desalinated ice forms on the walls of the container, fat floats to the surface, and protein is concentrated in the central and lower parts. When flaking, flakes and lumps form in the milk. The taste becomes watery and sweet.

Colostrum milk obtained within seven days after calving does not withstand pasteurization, has high acidity and an increased content of albumin, globulin and salts. Not subject to processing.

Old milk produced within 7-10 days before milking is stopped has a salty and rancid taste due to changes in mineral composition and the presence of lipase. Butter from such milk is unstable during storage, the cheese is of poor quality. Old milk is not accepted.

Use in cooking. Milk has a wide range of applications in cooking: it is used in the preparation of first and second courses, as well as various sauces, additives that give the product a specific taste of milk.

Storage, transportation, packaging and labeling. Milk is stored in well-ventilated and darkened rooms: pasteurized at a temperature of 0 to 8 °C for no more than 36 hours from the end of the technological process; sterilized - from 1 to 10 ° C up to 6 months; from Odo 20 °C no more than 4 months.

Milk is transported in different types of containers: tanks, flasks, canisters, from which it is poured into bottles with a capacity of 0.25; 0.5; 1.0 l and in plastic bags, as well as in cardboard bags with special polymer coatings of various capacities; in refrigerated or isothermal means of transport, ensuring that the optimum air temperature is maintained and thus the safety of the product.

The marking is applied to the milk packaging with indelible paint or embossing and includes the following information: product name, manufacturer's trademark, volume in liters, date of the deadline for implementation, designation of the regulatory document, fat percentage.

Requirements for the quality of drinking milk

Requirements for the quality of drinking milk are set out in GOST R 52090-2003 “Drinking milk. Specifications". The following terms are used for this:

• homogeneous batch of milk or cream - their various types, produced by one enterprise, equally processed, of the same name, produced in one work shift, packaged in uniform containers from one milk storage tank;
• average sample - a part of the goods taken from the control units of the packaging of a homogeneous batch in one dish. A package unit is a box, a flask, a tank compartment, etc.;
• average sample - a certain part of the average sample allocated for laboratory testing.

Sampling for commodity examination, preparation of samples for research are carried out in accordance with the standards.

Each batch of milk accepted into the distribution network must have accompanying documents: on the quantity - an invoice, the waybill of the manufacturer, on the quality - a certificate. When receiving milk:

• pay attention to the appearance of the container;
• on the state of the surface, the presence of deformation or rust on the metal container; dirt, chips on glass bottles; tightness of paper or polymer containers;
• compare the shelf life of the labeling and accompanying documents;
• determine the temperature of the incoming milk.

Acceptance of milk by quantity is carried out by a continuous check of the entire batch.

When accepting milk for quality, they check the compliance of the milk quality with the accompanying documents of the supplier. The quality of milk is established for each homogeneous batch by inspection of the average sample and the average sample in accordance with GOST.

A certain number of packaging units are selected from the incoming batch of goods in accordance with the requirements of GOST.

Organoleptic indicators of milk and dairy products are evaluated separately for each controlled packaging unit. According to organoleptic indicators, the product must meet the following requirements:

• appearance - opaque liquid; for fat and high-fat milk, a slight settling of fat is allowed, which disappears when stirred;
• consistency - liquid, homogeneous, non-viscous, slightly viscous; free of protein flakes and lumps of fat;
• taste and smell - characteristic of milk, without foreign tastes and odors, with a slight aftertaste of boiling; for baked and sterilized milk - a pronounced aftertaste of boiling; for reconstituted and recombined, a sweetish aftertaste is allowed;
• color - white, uniform throughout the mass; for baked and sterilized milk - with a creamy tint; for fat-free - with a slightly bluish tint.

To determine the physico-chemical parameters, an average sample is isolated from the average samples, which is placed in a clean container and sealed or sealed with the seals of the recipient and the supplier that sent the representative for sampling. Samples for analysis are sent to a laboratory that is not part of the system of the recipient or supplier. These samples are supplied with accompanying documents indicating the name of the enterprise that developed the product, the current standard for the product, the name and grade of the product, the temperature of the product at the time of taking the average sample. Studies are carried out no later than 4 hours from the time of sampling. The results of the commodity examination are compared with the norms of the standard given in Table. 1.8 and 1.9.

Table 1.8. The values ​​of the mass fraction of fat in drinking milk

Table 1.9. Physical and chemical indicators of milk quality

When examining the quality of milk, defects of various origins can be detected - feed, bacterial and physico-chemical. Milk defects are deviations of organoleptic indicators, chemical composition, packaging and labeling of milk from the indicators provided for by the standard, arising from the use of poor-quality raw materials, violation of technological regimes and storage. Their presence in milk significantly reduces the quality of the product or even does not allow milk to be sold for sale if the defects are very pronounced.

Feed defects arise when milk absorbs pungent odors of feed, premises, etc. These defects are eliminated or weakened by deodorization of milk, heat treatment.

Defects of bacterial origin can greatly change the taste and smell, consistency and color of milk. During storage, these defects increase.

Defects of feed and bacterial origin include taste defects: sour taste occurs as a result of the vital activity of lactic acid bacteria; rancid taste is formed during storage of milk, under the influence of lipase enzymes on the fatty part; bitter taste is caused by the presence of wormwood and putrefactive peptonic bacteria in the feed; salty taste is a consequence of diseases of the udder of animals.

Color defects - blue, redness or yellowing of milk - appear under the influence of pigmenting bacteria.

Odor defects are caused by the waste products of putrefactive bacteria, specific odors of feed. These include: barn, cheese, rotten, garlic, etc.

Consistency defects (thick, viscous, slimy consistency) result from the vital activity of lactic acid bacteria and mucus-forming bacteria.

To vices physico-chemical origin include: colostrum and old milk, non-churning milk, milk with a greasy taste (from exposure to ultraviolet rays), frozen milk.

Under the defects of milk understand the deviation of its properties from the normal state. Milk defects are expressed in changes in consistency, color, smell and taste.

Consistency defects: mucus or viscosity of milk, curdled milk, fermenting milk.

Sliming of milk with a sharp increase in acidity is caused by mucus-forming races of lactic acid microbes (Dutch streptococcus, mucus-forming race of Bulgarian lactobacillus, etc.).

Sliming of milk without a sharp increase in acidity is characterized by the fact that the milk remains liquid, but translucent accumulations of mucus appear on its surface. The causative agent of such mucus is a microbe close to Vast. aerogenes, but not gas generating. This defect occurs during prolonged storage of milk at temperatures below 10 ° C.

Mucus in milk is also observed when colostrum, which usually has a mucous consistency, is mixed with normal milk.

Curdled milk is distinguished by the fact that flaky curdled clots appear in it without a noticeable increase in the acidity of the milk, and this milk coagulates when heated. The cause of this defect is the various races of microbes that produce rennet, which causes sweet coagulation of milk.

Color defects: blue, red and yellow milk. The blue color of milk is rare and is caused both by some microorganisms and by some herbs, the coloring substances of which pass into milk.

The vices of smell and taste are very diverse both in their manifestation and in the causes that cause them. First of all, it should be noted that milk very quickly and easily absorbs any odors from the air, and therefore storage and transportation of milk together with other products that emit any odor (fish, meat, onions, kerosene, etc.) are unacceptable.

Through the digestive apparatus of the cow, bitter, ethereal, poisonous substances are transferred from the feed to milk. Most feed products are reflected in the taste and smell of milk. The bitter taste of milk is caused by: wormwood, buttercups, tansy, hare cabbage, as well as giving peas and beans in large quantities. Wild onions and garlic, which cows eat in large quantities. number in the spring in water meadows, cause a strong garlic-onion smell in the milk, making it unsuitable for consumption. Milk acquires a rare taste when cows are fed tops of rutabaga, turnips, when cattle graze on stubble covered with colza and field mustard, wild radish. Wild sorrel and sorrel contain a large amount of oxalic acid, which, passing into milk, increases the acidity of milk and causes it to coagulate prematurely. A sharp taste in milk is caused by fresh nettles, hops, water buckwheat - pepper, etc. A pronounced cabbage smell in milk is caused by large summer cottages of cattle.

Taste and odor defects such as rare, cabbage, fodder, manure can also be caused in milk by individual races of Escherichia coli and fluorescent bacteria, i.e., mainly by manure microflora.

Among other defects caused by microbes, one should point out the bitter taste of milk, which appears under the influence of putrefactive pentonic microbes at a low (below 10 ° C) storage temperature of milk, which suppresses the development of lactic acid microbes.

The reason for rancidity of milk is the splitting of its fat into glycerol and fatty acids and further changes in oleic acid and glycerol with the formation of aldehydes and ketones, which have a sharp taste, strongly irritating the mucous membranes of the oral cavity, intestines, etc.

Fat found in milk under the influence of fluorescent microbes Bact. fluorescens, Bact. putidum and other related races decomposes with the formation of aldehydes and ketones.

At low temperatures (below 10°C) and long-term storage, fluorescent microbes develop in milk, which produce the enzyme lipase, which breaks down fats.

A rancid taste can be in old milk (before starting a cow) and in colostrum due to incomplete synthesis of fats or partial breakdown of them by a large amount of lipase found in such milk.

Thus, the addition of colostrum or old milk gives normal milk a rancid taste.

The soapy taste of milk occurs under conditions of insufficient development of lactic acid microbes (below 10 ° C) during long-term storage of milk enriched with putrefactive microflora and fluorescent microbes. Soapy taste, apparently, is formed under the influence of alkaline products of protein breakdown and saponification of fats.

The sour taste of milk is caused by the development of lactic acid microbes, as well as E. coli at temperatures above 10 ° C.

Fermenting milk is a common vice. This defect is characterized by abundant release of gases in milk, forming foam under the settled cream. At the same time, various odors are formed in parallel - alcohol, yeast, manure, butyric acid, etc. The factors causing this defect are the Coli-aerogenes groups, yeast and butyric microbes. With severe contamination of milk with manure microflora and low storage temperature, the developing group of Coli-aerogenes produces carbon dioxide and forms an “unclean”, up to “dung”, smell in milk.

Infection of milk with yeast causes an alcoholic fermentation process with the release of carbon dioxide. When cows are fed unsuccessfully prepared ensiled feed, infection of milk with butyric microbes can occur. When storing such milk at low temperatures, the butyric fermentation process causes the formation of butyric acid and the release of gases - carbon dioxide and hydrogen; milk foams strongly and has a sharply unpleasant odor, which does not arise as a result of butyric fermentation, but as a result of the formation of products under the influence of a putrefactive process, which usually goes in parallel with butyric.

The taste of salted fat in milk appears under the action of sunlight (ultraviolet spectrum), directly falling on milk. Under the influence of ultraviolet rays, oleic acid found in milk fat, as unsaturated, attaches one or two water residues (HO) to itself and passes into hydroxy- or dihydroxystearic acid, which emits a disgusting smell of salted fat (tallow candle, greasy kitchen rag). Short-term, within a few minutes, exposure to sunlight on milk causes this defect.

Upon receipt of milk with defects at a dairy plant or a drain point, after identifying the nature and causes of these defects, the plant must take all measures to eliminate this phenomenon.

DEFECTS IN MILK

Milk defects are caused by the poor quality of feed, the ingress of microflora into milk, improper processing technology, violation of storage conditions and terms, and other reasons.

Consistency defects are caused by the vital activity of certain microorganisms. Milk acquires a thick consistency with the participation of lactic acid bacteria, mucous or viscous - under the action of mucus-forming bacteria. As a result of the development of E. coli bacteria, milk undergoes fermentation and foam is formed. When rennet-producing bacteria enter, the milk coagulates during heating even at low acidity.

Odor defects are most often caused by specific feed odors or unsanitary conditions of the premises in which animals are kept. Smell defects include barnyard, rotten, cheesy, garlic, etc.

Taste defects are the most common type of defects:

milk acquires a sour taste as a result of the vital activity of lactic acid bacteria or E. coli;

rancid taste is formed in milk during its long-term storage at low temperatures under the action of lipase enzymes, and also appears in the milk of the last days of lactation;

bitter taste is due to the activity of putrefactive peptonic bacteria in milk, can be caused by the presence of wormwood in feed;

unpleasant specific flavors can appear from the presence in the diet of animals of nettle, garlic, onion, turnip, radish, field mustard, etc .;

salty taste appears in some diseases of the udder;

milk acquires a metallic taste as a result of the interaction of lactic acid with the metal of the container;

a greasy taste occurs when milk is stored in the light as a result of the oxidation of milk fat by atmospheric oxygen;

smoky taste and smell are possible in sterilized milk and packages if the paper is burned when gluing the transverse seams of the package.

Color defects (redness, blue and yellowing) appear under the influence of pigmenting bacteria. Sometimes the yellowing of milk is associated with the ingress of blood into the milk during milking due to the diseased state of the animal. Color defects - blue, redness or yellowing of milk - appear under the influence of pigmenting bacteria.

The defects of physical and chemical origin include: colostrum and old milk, non-churning milk, milk with a greasy taste (from exposure to ultraviolet rays), frozen milk.

When milk freezes, its quality noticeably decreases: the colloidal state is disturbed, as a result of which the milk is stratified; desalinated ice forms on the walls of the container, fat floats to the surface, and protein is concentrated in the central and lower parts. When flaking, flakes and lumps form in the milk. The taste becomes watery and sweet.

Colostrum milk obtained within seven days after calving does not withstand pasteurization, has high acidity and an increased content of albumin, globulin and salts. Not subject to processing.

Old milk produced within 7-10 days before milking is stopped has a salty and rancid taste due to changes in mineral composition and the presence of lipase. Butter from such milk is unstable during storage, the cheese is of poor quality. Old milk is not accepted.

Defects of fodder origin occur when milk absorbs pungent odors of feed, premises, etc. These defects are eliminated or weakened by deodorization of milk, heat treatment. Defects of feed and bacterial origin include taste defects: sour taste occurs as a result of the vital activity of lactic acid bacteria; rancid taste is formed during storage of milk, under the influence of lipase enzymes on the fatty part; bitter taste is caused by the presence of wormwood and putrefactive peptonic bacteria in the feed; salty taste is a consequence of diseases of the udder of animals.

Defects can be characteristic of freshly milked milk, as well as occur during storage as a result of the vital activity of microorganisms. This significantly changes the composition and organoleptic properties of milk.

Taste and odor defects.

Sour taste (high acidity) is due to the activity of lactic acid bacteria in violation of the modes and terms of storage of milk.

The rancid taste is manifested by the hydrolysis of fat by the action of milk lipase or lipase of microorganisms at low storage temperatures. The defect is often detected when old milk containing a significant amount of lipase is ingested.

Bitter taste occurs when proteins break down to form peptones, which have a bitter taste. The decomposition of the protein is due to the action of peptonizing bacteria that enter and develop in milk in case of violations of the sanitary and hygienic regime for its production, storage and transportation at temperatures below 10 ° C; occurs more frequently in reconstituted milk.

A bitter taste also occurs when there are significant amounts of bitter plants in the feed.

The oxidized taste is also called oleic, greasy, metallic, or sunny. It is caused by the accumulation of fat oxidation products in milk: hydroxy acids, aldehydes, ketones. The reasons for the appearance of this defect are the action of sunlight, ultraviolet rays, air, high temperature, as well as the storage of milk in untinned iron and copper dishes, since metals, especially copper, contribute to the oxidation of milk fat.

A salty taste appears due to a change in the salt composition of milk in certain diseases of the animal.

Feed tastes and odors arise from the transition from feed to milk of characteristic flavoring substances and essential oils.

For this reason, various flavors and odors may appear in milk: wormwood, garlic-onion, rare, silage, cabbage, etc.

Extraneous tastes and odors appear as a result of the absorption of volatile compounds (hydrocarbons, esters, ketones, etc.) by milk. Therefore, joint storage and transportation of milk with strong-smelling products is not allowed.

Milk that has the indicated defects in taste and smell is not allowed to be sold as drinking milk intended for direct consumption; it is sent for processing.

Color defects. Milk can take on red, pinkish, blue, blue or yellow hues. Changes in the natural color of milk are associated with the development of pigment-forming bacteria in it, some yeasts and ingestion of blood from a damaged udder, eating herbs with pigments by animals, with certain diseases (with mastitis and tuberculosis - bluish, with foot-and-mouth disease - yellow), mixing with colostrum (yellow) , storage of milk in zinc dishes (bluish).

Consistency defects. Sometimes milk acquires a slimy (viscous), curdled or frothy texture. This is due to the activity of various microorganisms in violation of the modes and periods of storage of milk.

All deviations from the normal organoleptic parameters of milk are called defects. The causes and timing of milk defects are varied. Thus, a number of taste and odor defects may appear in milk before milking. These include defects caused by changes in the chemical composition of milk in violation of physiological processes in the body of animals (at the beginning and end of lactation, in case of illness, etc.) and the entry of feed substances with a specific taste and smell into the mammary gland with blood. For example, colostrum, old-milk milk and milk from animals with mastitis, ketosis and other diseases have pronounced flavors (bitter, salty, cow, etc.). The most common feed flavors (silage, cabbage, garlic, etc.) and odors pass into milk when animals are fed certain feeds, herbs and weeds.

Other defects in taste and smell can occur in milk after milking - in case of violation of the rules for storage, transportation and primary processing of milk. So, rancid, oxidized, soapy and some other tastes and odors of milk are the result of lipolysis and fat oxidation. Various defects are predetermined by the absorption of odors from poorly washed containers, the lack of ventilation of the room in which milk is stored, the absorption of the smell of lubricating oils, gasoline, etc., as well as contamination of milk with detergents and disinfectants, drugs, pesticides and other chemicals.

Usually, defects in the taste and smell of milk are grouped according to the nature of the causes of their occurrence: defects of feed, bacterial, technical (technological) and physico-chemical origin.

Defects that are the result of lipolysis. Due to lipolysis, the taste and smell of milk becomes unpleasant, rancid. The reason for this is free low molecular weight fatty acids: butyric, caproic, caprylic, capric and lauric. They can accumulate in raw materials, as well as be formed during the processing and storage of milk due to fat hydrolysis under the action of heat-resistant milk lipases or lipolytic enzymes of psychrophilic bacteria that enter milk during re-contamination (from equipment, containers, air, etc.).

Defects that are a consequence of the oxidation of the lipid fraction. Oxidation of lipids by oxygen in the air is a common cause of undesirable flavors in milk: cardboard, metallic, oily, greasy, fishy and others, which are combined under the general term "oxidized" flavor.

The precursors of the oxidized taste are unsaturated fatty acids of phospholipids and triglycerides of milk fat - arachidonic, linolenic, linoleic, oleic acids and their isomers. Oxidation of fatty acids by molecular oxygen occurs through chain reactions (see v.2).

The oxidized taste of milk is determined by carbonyl compounds - numerous saturated and unsaturated aldehydes and ketones. Their certain concentrations and combinations give the products the corresponding specific foreign flavors: fishy, ​​rancid, metallic, cardboard. It is characterized by a pungent astringent taste, which is sometimes accompanied by metallic, fishy, ​​greasy and oleic flavors.

In pasteurized and raw milk, during prolonged storage at low temperatures, spontaneous oxidation of the phospholipid membranes of fat globules and free milk fat occurs. As a result, a cardboard taste also appears.

Destabilization of the fatty phase, ions of copper, iron, light accelerate the appearance of an oxidized taste. This is because free (destabilized) fat contains more polyunsaturated fatty acids. The amount of free fat in milk depends on the season (more in winter than in summer), the degree of mechanical interference during storage, and other factors.

The appearance of an oxidized taste in milk can be prevented by reducing the influence of mechanical factors, adding ascorbic acid (25 mg or more per 1 liter), pasteurization at high temperatures and homogenizing milk: ascorbic acid in low concentrations acts as a pro-oxidant, and with an increase

Chapter 2. Milk and dairy products concentration - as an antioxidant. The antioxidant properties of milk are enhanced by SH-groups, which are released during high-temperature pasteurization. Heat treatment and homogenization of milk reduce the pro-oxidant activity of copper and iron due to the formation of inactive complexes with proteins and SH-groups.

Defects that occur under the influence of light. Bottled milk is often stored on lighted counters and display cases before being sold. Under the action of light due to photooxidation of lipids, oxidized flavors appear in milk. At the same time, the biological value of milk decreases, carotene, ascorbic acid, riboflavin and other vitamins are destroyed.

The mechanism of lipid photooxidation is similar to the mechanism of oxidation with atmospheric oxygen, i.e. has a chain free radical character. At the same time, the oxidation of lipids by molecular oxygen during storage of milk at low temperatures lasts slowly, and light causes oxidative spoilage much faster.

During photooxidation in milk, proteins first change, and then milk fat. Accordingly, a sunny and oxidized aftertaste appears.

In addition, under the influence of light, fodder (cabbage) and burnt flavors may occur.

Sunny aftertaste is characteristic of homogenized milk. When storing packaged milk near fluorescent lamps, a change in taste occurs after 2-4 hours. The development of the defect is catalyzed by ascorbic acid. Over time, the salisty taste turns into an oxidized one, the appearance of which is catalyzed by copper and is determined by the oxidation of lipids.

Defects associated with heat treatment. In the process of pasteurization and sterilization, carbohydrates, lipids and amino acids of milk and cream undergo profound changes with the formation of numerous compounds that have specific taste and smell. During storage, changes in the constituent parts of milk can be prolonged, and the decay products, when interacting with each other, form new components that worsen its taste and smell. Compounds that adversely affect the taste and smell of milk include furfural, benzaldehyde, maltol, acetophenone, o-aminoacetophenone and benzthiazole.

These compounds accumulate as a result of reactions of melanoidin formation (saccharoamine reactions) when milk is heated to high temperatures.

The defects that appear in milk immediately after heat treatment include the taste of overpasteurization, caramelization and burnt taste - the specific taste of pasteurization, due to the release of sulfidryl groups and hydrogen sulfide from protein molecules, is not a defect.

The taste of repasteurization occurs at high processing temperatures (130-150 ° C) or prolonged heat treatment. This taste is sharper (compared to the taste of pasteurization) and does not disappear during storage.

The mechanism by which caramelization taste occurs is not yet fully understood. It is very complex and is caused by products of non-enzymatic darkening of milk (acids - fumeric, lactic, pyruvic; heterocyclic compounds - derivatives of furan, pyrol, pyran, aldehydes, phenols, etc.).

The burnt taste is caused by the formation of a burn on the surface of the heating apparatus.

Defects of biochemical origin associated with the activity of microorganisms. The most common among them are:

• souring of milk (due to the development of lactic acid bacteria in raw milk or butyric bacteria in pasteurized milk),
• malt flavor - predetermines acetaldehyde, which is a waste product of microorganisms,
• fruity taste as a result of the development of psychrophilic bacteria,
• bitter taste can appear in milk when stored in refrigerators for more than a specified period. Low temperatures retard the development of acid-forming bacteria and thus create conditions for the development of putrefactive bacteria, which contribute to the formation of a bitter taste in milk. In the first stage of putrefaction, proteins decompose to form albumose and peptones, which have a bitter taste.

The defects of the biochemical origin also include a defect in the consistency of milk - ductility. This defect appears due to the development of bacteria, which, forming capsules, give the milk a slimy, viscous consistency.

Color defects in milk are very rare. They may appear due to the development of pigment-forming bacteria (yellowing, blue, reddening of milk). Sometimes the discoloration is associated with the ingress of blood into the milk when milking animals in a diseased state.