INFLUENCE OF HEAT TREATMENT ON THE PROPERTIES OF MILK
Heat treatment of dairy raw materials is carried out for the purpose of its disinfection. It should ensure not only reliable suppression of the vital activity of microorganisms, but also the maximum possible preservation of the original properties of milk. Any thermal effect on milk disrupts its original composition and physicochemical properties. The degree of physicochemical changes in the components of milk depends mainly on the temperature and duration of heat treatment.
Milk proteins are denatured by heat. Whey proteins are the most heat-sensitive, denatured at temperatures above 65 °C, while casein has high heat resistance. At temperatures above 100 °C, partial decomposition of lactose begins, as a result of which milk acquires a specific taste, smell and color (brown). Milk fat remains virtually unchanged when heated to 100 °C. During heat treatment, vitamins are partially destroyed, especially water-soluble ones (C, B12, thiamine, etc.), and enzymes (reductase, phosphatase, peroxidase) are also inactivated. As a result of the transition of soluble calcium and phosphorus salts to an insoluble state, mineral salts partially precipitate. Changes in milk components that cause a negative effect on nutritional value and organoleptic properties should be insignificant.
Types of heat treatment include pasteurization, sterilization and thermization.
Pasteurization of milk– This is the heat treatment of milk in order to destroy vegetative forms of microflora, including pathogenic ones. The pasteurization regime should also ensure that the desired properties of the finished product are obtained, in particular organoleptic characteristics (give taste, desired viscosity, curd density).
The effect of pasteurization, determined by the degree of death of pathogenic microflora, influences the choice of modes and methods of pasteurization. Of the pathogenic microorganisms, tuberculosis bacteria are more resistant to heat treatment. Since the work of identifying the causative agents of tuberculosis is complex, the effectiveness of pasteurization is usually determined by the death of no less persistent E. coli. The effect of pasteurization depends on the temperature (t) and duration of heat treatment (z), the relationship of which is established in the form of the following equation: ln z = 36.84 – 0.48 t, where 36.84 and 0.48 are constant values. Depending on these factors, three pasteurization modes are distinguished: long-term pasteurization - at a temperature of 60–63°C with holding time for 30 minutes; short-term – at a temperature of 74–78 °C with a holding time of 20 s; instant - at a temperature of 85–87 °C or 95–98 °C without holding.
The choice of pasteurization modes is determined by the technological conditions and properties of the product. If the product contains components with low heat resistance, long-term pasteurization should be used. The process of long-term pasteurization, although it ensures reliable destruction of pathogenic microbes and the least change in the physicochemical properties of milk, however, requires large costs associated with the use of low-performance equipment.
The most common method in the production of pasteurized milk, fermented milk products, and ice cream is short-term pasteurization. This method is also reliable for inactivating microbes and maximizing the preservation of the original properties of milk. Instant pasteurization has the same effect on microbes and milk properties as short-term pasteurization. It is recommended for the pasteurization of cream, from which butter is produced, and in the production of canned milk. Thus, all pasteurization methods make it possible to obtain a product that is harmless for direct consumption, but has a limited shelf life.
The resistance of microorganisms to heat treatment increases with increasing fat and dry matter content in products (cream, ice cream mixture), since fatty and protein substances have a protective effect on microbial cells. Therefore, for products with a high content of fat and solids, the pasteurization temperature should be increased by 10–15% compared to the pasteurization temperature of milk.
Simultaneously with the pasteurization process, to improve the organoleptic characteristics of milk and cream, they are deodorized. Changes in organoleptic characteristics occur due to the presence of volatile substances and gases in milk, especially oxygen, which cause undesirable taste and smell. Oxygen present in milk during storage contributes to the oxidation of the fat fraction and the destruction of vitamins. Vacuum deodorization units are used to remove these unwanted substances from milk. Deodorization is usually carried out at a temperature of 65–70 °C and a vacuum of 0.04–0.06 MPa for 4–5 s. Under these conditions, the milk boils, and unwanted gases and volatile substances are removed along with the vapor.
One of the types of pasteurization is thermization.
Thermization– This is the heat treatment of milk in order to increase its shelf life by reducing the overall bacterial contamination of milk. It is carried out at a temperature of 65 °C for 15 s. Thermization as a low-temperature short-term heat treatment is recommended to increase the stability of raw milk during storage. In cheese making, thermization is used to process milk with increased bacterial contamination and intended for ripening, and in the production of canned milk - to increase the heat resistance of milk.
People constantly strive to learn how to extend the life of products, but at the same time technologies are being developed that do not in any way affect the beneficial properties. Pasteurization technology was discovered in the 19th century by a man named Louis Pasteur. It was he who became the founder of immunology and discovered the possibilities of heat treatment of products, which can significantly increase their shelf life.
What it is?
You can often find milk and other products on store shelves that indicate that they are pasteurized. In fact, such a complex word just means that the milk was processed at high temperature, that is, it was heated, but not boiled, because then it would lose its beneficial properties. It is enough to heat it to 60 degrees and hold it at this temperature for half an hour to destroy pathogenic bacteria. If the temperature reaches 80 degrees, then 20 minutes is enough.
This time is enough for some of the bacteria to die, and the other part to reduce activity.
The pasteurization process has a beneficial effect on the shelf life of the drink, regardless of whether it was produced on an industrial scale or purchased on a farm.
Many young housewives do not know whether it is possible to pasteurize a product at home and what is needed for this. Indeed, pasteurization of milk at home is possible. They use not only a gas stove, but also an oven; you can even pasteurize it in a slow cooker.
If you buy milk in a tetra pack, then it is recommended to heat it not in a saucepan, but to place the package in a container with heated water. In fact, the pasteurization process will be the same, only the beneficial properties will be better preserved and the drink will undergo fewer changes. The process is carried out once, which is enough to protect yourself. Milk will not become better if it is constantly boiled, but the beneficial properties will become less and less each time.
As a useful tip, it is recommended to cool the fresh milk immediately, otherwise it will turn sour in a few hours at its own temperature. It is best to keep milk in the refrigerator in glass containers. But storing the drink in metal and plastic containers is not recommended, since the materials can react with the liquid and impart negative qualities to it.
Using a multicooker
There is only one way to properly prepare pasteurized milk in a slow cooker, and this is due to the properties of household appliances. When the equipment appeared in the kitchen of the modern housewife, it made many processes easier. Stews, grains, and more are cooked wonderfully inside. You can also easily pasteurize milk in it without having to stand at the stove and watch for it to escape. Moreover, it is not time that plays a decisive role, but temperature during the heat treatment process, therefore it is not easy to regulate the degree of heating.
With a multicooker, everything is easy: the appliance has a mode, all the housewife needs to do is set it and press a button. If you are processing homemade milk, just set it to 80 degrees and set the timer for 20 minutes. New multicookers have an additional mode, which is called “pasteurization”. You just need to pour the milk into the container, put it inside and press the appropriate button.
Kinds
In order for the drink to be well stored even in its processed form, the container into which it is then poured for storage must also undergo heat treatment. It is best to use glass jars that have a tight lid.
There are several types of pasteurization depending on the temperature at which it is carried out:
- long-term;
- ultra-high temperature;
- short-term high temperature.
The thirty-minute heat treatment process is called long-term pasteurization. At the same time, the temperature remains at 60 degrees. In terms of destroying microorganisms, this is the most time-consuming but also effective method.
It is impossible to carry out high-temperature short-term treatment at home; this type of pasteurization is typical for industrial facilities. The procedure requires special equipment that can heat milk and cool it in a few minutes. One of the significant disadvantages of this type of processing is accuracy: if you do not hold milk for a few seconds, the microorganisms will not die, but if you hold it too long, it will lose all its beneficial properties.
This is one of the reasons why pasteurized milk differs in quality at different enterprises. Even different batches of a drink from the same plant may differ in their properties.
As for instant heating, it was originally invented for mothers who are sick with HIV, and therefore cannot feed their children breast milk. The method is available for use at home, but to implement it you will need to organize a water bath. For pasteurization you will need 2 containers: one large and the other smaller. Water is poured into the first and put on fire, the second with milk is placed on water. As soon as the first pan begins to boil, you can remove the milk from the heat.
Will there be any benefit?
There are many opponents of the process of heat treatment of milk, who believe that the moment it is heated, it loses its beneficial properties and becomes useless for the human body. They argue that pasteurizing a drink is necessary only to increase its shelf life and nothing more. Due to ignorance of many nuances, they, without knowing it, talk about sterilization when the temperature of the milk reaches 100 degrees. Only in this case does the destruction of useful compounds occur, but not during the pasteurization process, when the maximum temperature reaches 80 degrees.
The method allows you not only to increase the shelf life of the product, but also to protect yourself, which is important when milk from a farm is consumed as food.
You will learn more about how milk is pasteurized in the following video.
Pasteurization
Louis Pasteur.
Pasteurization- process disposable heating most often liquid products or substances to 60 °C for 60 minutes or at a temperature of 70-80 °C for 30 minutes. The technology was proposed in the mid-19th century by French microbiologist Louis Pasteur. It is used to disinfect food products, as well as to extend their shelf life.
With such processing in the product vegetative forms die microorganisms, however disputes remain in a viable state and when favorable conditions arise, they begin to develop intensively. Therefore, pasteurized products (milk, beer, etc.) are stored at low temperatures for a limited period of time. It is believed that the nutritional value of products remains virtually unchanged during pasteurization, since the taste and valuable components (vitamins, enzymes) are preserved.
Depending on the type and properties of food raw materials, different pasteurization modes are used. Distinguish long-term(at a temperature of 63-65 °C for 30-40 minutes), short(at a temperature of 85-90 °C for 0.5-1 min) and instant pasteurization (at 98 °C for a few seconds).
Pasteurization cannot be applied when canning products, since hermetically sealed containers are a favorable environment for the germination of spores of anaerobic microflora (see botulism). For the purpose of long-term preservation of products (especially those initially contaminated with soil, for example, mushrooms, berries), as well as for medical and pharmaceutical purposes, fractional pasteurization is used - tindalization.
Behavior of bacteria during pasteurization
Mesophilic lactic acid bacteria (S. lactis, S. cremoris, etc.) mostly die during pasteurization. Thermophilic lactic acid streptococci and enterococci (S. durans, S. bovis, S. faecalis) remain in milk after pasteurization in quite significant quantities. However, their biological activity during milk storage at temperatures below 8°C is relatively low, and they do not affect the quality of chilled pasteurized milk. Heat-resistant lactic acid sticks also withstand accepted pasteurization regimes. However, at low milk storage temperatures they do not develop. Their role is especially great in the production of fermented milk products, where elevated ripening temperatures and the presence of lactic acid streptococci stimulate their development. Psychrotrophic bacteria mostly die during pasteurization, although individual cells of more heat-resistant species can withstand short-term pasteurization at temperatures of 71-72°C and even 75-77°C. The effectiveness of pasteurization depends on what types of microorganisms predominate in raw milk. This factor, in turn, is determined by the storage conditions of raw milk before pasteurization. If milk is cooled to a temperature of 0-3°C immediately after milking and stored at this temperature until processing, predominantly psychrotrophic microflora develops in it. Psychrotrophs have low heat resistance, so the efficiency of pasteurization of deep-chilled milk is high (up to 99.9%). Developing in raw milk, psychrotrophs can produce heat-resistant lipids and proteases that are not destroyed by heat treatment, which can have a negative impact on the quality of sterilized milk and canned milk. If milk is stored at temperatures above 8-10°C, heat-resistant bacteria (enterococci, thermophilic streptococci, etc.) predominate in it, reaching 50% or more of the total number of microorganisms. As a result, the efficiency of milk pasteurization is below 98%.
Sources
- Pasteurization- article from the Great Soviet Encyclopedia
- Commodity research and examination of food products: Textbook / Ed. prof. L. G. Eliseeva. - M.: MCFR, 2006.
Notes
see also
Links
Wikimedia Foundation. 2010.
Synonyms:See what “Pasteurization” is in other dictionaries:
Heating grape wine and other liquids to a certain temperature to protect them from the development of harmful microorganisms; the method is named after them. Pastors. Dictionary of foreign words included in the Russian language. Pavlenkov F., 1907.… … Dictionary of foreign words of the Russian language
pasteurization- and, f. pastérisation f. Sterilization of wine according to Pasteur's method to protect it from spoilage, as well as to improve its quality. Chudinov 1902. || ext. Destruction of microorganisms in liquids by heating no more than 100º. Pasteurization... ... Historical Dictionary of Gallicisms of the Russian Language
A method for destroying vegetative forms of microorganisms in liquid media and food products by heating them once and briefly to temperatures below 100 °C. Normal pasteurization mode – 60 - 70 °C for 15-30 minutes. It is applied for… … Dictionary of microbiology
Pasteurization, actinization, biorization Dictionary of Russian synonyms. pasteurization noun, number of synonyms: 3 actinization (1) ... Synonym dictionary
Heating food during canning to temperatures below 100°. Dictionary of culinary terms. 2012… Culinary dictionary
PASTEURIZATION- one of the ways to destroy microorganisms by heating food products to a temperature not higher than + 100°. For the first time, this method of combating harmful microorganisms was proposed by the outstanding French microbiologist L. Pasteur and... ... Concise Encyclopedia of Housekeeping
PASTEURIZATION, a method of destroying microorganisms in liquids and food products by heating once (usually at 60-70°C for 15-30 minutes). Proposed by L. Pasteur. Used for canning milk, wine, beer, etc... Modern encyclopedia
A method of destroying microbes in liquids and food products by one-time heating to a temperature below 100.C (usually 60-70.C) with different exposure times (usually 15-30 minutes). Proposed by L. Pasteur. Used for canning milk, wine, beer and... ... Big Encyclopedic Dictionary
PASTEURIZATION, a controlled heat treatment of products designed to kill bacteria and other microorganisms, proposed by Louis Pasteur in the 1860s. Milk is pasteurized by heating it to a temperature of 72 ° C, at which it... ... Scientific and technical encyclopedic dictionary
- [te], pasteurization, plural. no, female (specialist.). Preventing liquids from developing harmful microorganisms by heating. (On behalf of the 19th century French bacteriologist Pasteur, who first used this method.) Ushakov’s explanatory dictionary. D.N. Ushakov. 1935... ... Ushakov's Explanatory Dictionary
PASTEURIZE [te], zuyu, zuesh; bathed; owls and nesov., that. Process (cook) food products by heating (not higher than 100 Ozhegov’s Explanatory Dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 ... Ozhegov's Explanatory Dictionary
Books
- Radiation technologies. Applications in laboratory research, materials science and nanotechnology, industry, Ilya Mikhailovich Obodovsky. The previously published book “Physical Foundations of Radiation Technologies” examines the issues of Energy loss of various types of radiation in matter. This study guide analyzes how the substance...
Pasteurization of milk or heat treatment is the process of heating milk from 63 ° C to a temperature close to the boiling point.
This process got its name from the famous French scientist Louis Pasteur (1822-1892), who first used this method to eliminate microorganisms in wine and beer.
The effect of pasteurization on microorganisms present in milk depends on the temperature to which the milk is heated and the duration of exposure at this temperature.
Pasteurization destroys bacteria, and sterilization (heating milk above boiling point) immediately destroys spores. Boiling destroys all microflora of milk, except for spores that are resistant to boiling temperatures. Pasteurization without noticeable changes in the organoleptic parameters of milk (taste, smell and consistency) destroys tuberculosis, brucellosis and other pathogenic bacteria.
In ordinary collected milk, 99% of microbes die only if the equipment, tools, and utensils used in the pasteurization process are well and reliably sterilized. Thus, the addition of contaminated milk containing 1 billion microbes to pasteurized milk (i.e., the amount that could accidentally remain in dairy equipment) will increase the number of bacteria in milk to 1 million in 1 ml. These bacteria will actively multiply and will inevitably lead to spoilage of all milk.
Pasteurization is therefore a more common and cheaper method of disinfecting milk.
Milk is also pasteurized during the production of all milk products in order to protect them subsequently from undesirable processes that are caused by the activity of bacteria and especially E. coli, butyric acid microbes, etc.
In practice they are used three pasteurization modes:
- during long-term pasteurization, milk is heated to 63-65 ° C and maintained at this temperature for 30 minutes; short-term pasteurization is carried out at 72-75 °C with holding for 15-20 s, which is carried out in a stream;
- instant pasteurization - heating milk to a temperature of 85-90 ° C without holding.
The thermal effect on milk leads to some changes in its constituent substances. When heated, the gases dissolved in milk evaporate from the milk. Due to the removal of carbon dioxide, the acidity of milk decreases by 0.5-1 °T.
At temperatures above 85°, casein partly changes. But milk albumin is most affected: at 60-65 °C it begins to denature.
The salt composition of milk is also disrupted during pasteurization. Soluble phosphate salts become insoluble. Due to the partial coagulation of proteins and the formation of insoluble salts, a sediment is deposited on the surface of heating devices (pasteurizers) - milkstone (burnt).
Pasteurized milk is curdled more slowly by rennet. This is explained by the precipitation of calcium salts. Adding a calcium chloride solution to such milk restores its ability to coagulate.
Heat treatment or pasteurization is the process of heating milk from 63 ºС to a temperature close to the boiling point.
This process got its name from the famous French scientist Louis Pasteur (1822-1892), who first used this method to destroy microorganisms in wine and beer.
The effect of pasteurization on microorganisms contained in milk depends on the temperature to which the milk is heated and the duration of exposure at this temperature.
Pasteurization destroys microbes, and sterilization (heating milk above boiling point) also destroys spores. Boiling destroys all microflora of milk, with the exception of spores that are resistant to boiling temperatures. Pasteurization without noticeable changes in the organoleptic properties of milk (taste, smell and consistency) destroys tuberculosis, brucellosis and other pathogenic bacteria.
In ordinary collected milk, 99% of bacteria die only under the condition of good, reliable sterilization of equipment, equipment, and utensils used in the pasteurization process. Thus, the addition of contaminated milk containing 1 billion bacteria to pasteurized milk (i.e., the amount that could remain inadvertently in dairy equipment) will increase the number of bacteria in milk to 1 million in 1 ml. These bacteria will actively multiply and will inevitably lead to spoilage of all milk.
Pasteurization, therefore, is the simplest and cheapest way to decontaminate milk.
Milk is also pasteurized during the production of all dairy products in order to protect them subsequently from undesirable processes that are caused by the activity of bacteria and especially E. coli, butyric acid bacteria, etc.
When cattle are kept on pasture, the microflora of milk is destroyed by heating more completely than when kept in stalls. This is explained by the fact that when kept in stalls, bacteria enter the milk mainly from manure particles. These bacteria are more resistant to heat due to their properties. When kept on pasture, milk contains mainly bacteria that multiply on plants. Before pasteurization, thorough cleaning of milk is necessary. In practice, three pasteurization modes are used:
during long-term pasteurization, milk is heated to 63-65 º C and maintained at this temperature for 30 minutes;
short-term pasteurization is carried out at 72-75 º C with holding for 15-20 s, which is carried out in a stream;
flash pasteurization - heating milk to a temperature of 85-90 C without holding.
Thermal effects on milk lead to some changes in its constituent substances. When heated, the gases dissolved in it evaporate from milk. Due to the removal of carbon dioxide, the acidity of milk decreases by 0.5-1 ºT.
At temperatures above 85°, casein partially changes. But milk albumin is most affected: at 60-65 °C it begins to denature.
The salt composition of milk is also disrupted during pasteurization. Soluble phosphate salts become insoluble. Due to the partial coagulation of proteins and the formation of insoluble salts, a milky sediment (burnt) is deposited on the surface of heating devices (pasteurizers).
Pasteurized milk is curdled more slowly by rennet. This is explained by the precipitation of calcium salts. Adding a calcium chloride solution to such milk restores its ability to coagulate.
Vitamins are resistant to high temperatures, especially if milk is heated without access to oxygen. Heating to high temperatures (80-85°) gives milk a special taste and aroma, which intensifies as the temperature rises. When boiling, the composition of milk also changes. For example, the content of vitamins A and C is reduced by almost 2 times. Nutrients ranging from 15 to 20 are lost due to the formation of sediments of proteins, fat and calcium salts on the walls of the dishes. Therefore, there is no special need to boil pasteurized milk.
At home, we can also recommend long-term pasteurization of milk, which can be done without much difficulty. It is produced through heated water. The milk poured into the pan is stirred with a clean spoon while heating. As soon as the temperature rises to 63-65 °C, heating should be stopped and maintained for 20-30 minutes. After this, place the pan with milk in cold water.