FREEZING AS A METHOD OF FOOD PRESERVATION ЗАМОРАЖИВАНИЕ КАК МЕТОД

The main reasons of fresh food spoilage are microorganisms that are present in plant and animal tissues and act destructively on raw material components. An additional effect on these factors have air, temperature, light and so on. Depending on the characteristics of raw materials, the reasons of their spoilage and a product that is to be produced, the appropriate principles and methods of preservation are used. To prevent product spoilage, it is necessary to create conditions of their storage or change their properties in such a way that microorganisms would be destroyed or could not develop and enzymes that regulate biochemical processes would be inactivated. The first methods of preservation were natural processes: salting, smoking, fermentation and so on. In 1810, French chef Nicolas Appert published a book on food preservation using heating. Later an English patent on food preservation in hermetically closed tin cans was registered. Multiple methods of food preservation consist mainly in regulation of vital processes both in raw materials and microorganisms. This is a basis of classification of plant raw material preservation by prof. Ya.Ya. Nikitinsky. It is necessary to pay attention to the fact that animal raw materials before preservation are not a living object and are different from plant objects, in which the processes of metabolism inside tissues and substance exchange with an environment (including the respiration process) are continued. Therefore, not all moments in classification of preservation methods are relevant to methods for preservation of meat from warm-blooded animals, fish and poultry. Regulation of life processes in this case concerns only raw material microflora. Введение Основными причинами порчи свежих пищевых продуктов являются присутствие в растительных и животных тканях микроорганизмов, которые разрушающе действуют на компоненты сырья. Дополнительное влияние на эти факторы оказывают воздух, температура, свет и т. д. В зависимости от характера сырья, причин его порчи и продукта, который необходимо получить, применяются соответствующие принципы и методы консервирования. Для предохранения продуктов от порчи необходимо создать такие условия их хранения либо так видоизменять их свойства, чтобы микроорганизмы или были уничтожены, или не могли развиваться, а ферменты, регулирующие биохимические процессы, были инактивированы. Первыми методами консервирования стали естественные процессы: соление, копчение, брожение и др. В 1810 г. французский кулинар Н. Аппер опубликовал книгу о консервировании пищевых продуктов с помощью тепла. Позднее был зарегистрирован английский патент на консервирование пищевых продуктов в герметически закрытых металлических банках. Многочисленные способы сохранения пищевых продуктов заключаются в основном в регулировании жизненных процессов в самом сырье и микроорганизмах. На этом основана классификация методов консервирования растительного сырья проф. Я. Я. Никитинского. Следует обратить внимание на то, что сырье животного происхождения перед консервированием не является живым объектом и отличается от растительных объектов, в которых после сбора урожая продолжаются процессы обмена веществ внутри тканей и с окружающей средой, в том числе и процесс дыхания. Поэтому не все моменты классификации методов консервирования касаются методов сохранения мяса теплокровных животных, рыбы, птицы. Регулирование жизненных процессов в этом случае касается лишь микрофлоры сырья. УДК/UDK: 664.9.03+ 664.8.037.1+ 664.8.037.51 DOI 10.21323/2414-438X-2017-2-2-43-59


Introduction
The main reasons of fresh food spoilage are microorganisms that are present in plant and animal tissues and act destructively on raw material components.An additional effect on these factors have air, temperature, light and so on.Depending on the characteristics of raw materials, the reasons of their spoilage and a product that is to be produced, the appropriate principles and methods of preservation are used.To prevent product spoilage, it is necessary to create conditions of their storage or change their properties in such a way that microorganisms would be destroyed or could not develop and enzymes that regulate biochemical processes would be inactivated.The first methods of preservation were natural processes: salting, smoking, fermentation and so on.In 1810, French chef Nicolas Appert published a book on food preservation using heating.Later an English patent on food preservation in hermetically closed tin cans was registered.Multiple methods of food preservation consist mainly in regulation of vital processes both in raw materials and microorganisms.This is a basis of classification of plant raw material preservation by prof.Ya.Ya.Nikitinsky.It is necessary to pay attention to the fact that animal raw materials before preservation are not a living object and are different from plant objects, in which the processes of metabolism inside tissues and substance exchange with an environment (including the respiration process) are continued.Therefore, not all moments in classification of preservation methods are relevant to methods for preservation of meat from warm-blooded animals, fish and poultry.Regulation of life processes in this case concerns only raw material microflora.

Classification
Three main groups of methods for raw material and food preservation are distinguished: 1. Methods based on the biosis principle, i.e., maintenance of the life processes in raw materials and the use of their innate immunity.
Biosis consists in food storage in a fresh form without any special treatment.Only measures aimed at maintenance of normal life processes and some restriction of their intensity are taken.Biosis is not a method of preservation in general meaning, but only a system of measures that ensures short-term storage of raw materials in fresh form upon its entering to processing.
The anabiosis principle is a basis of several preservation methods: cooling, freezing, creation of high concentrations of osmotically active substances, drying, storage in a regulated atmosphere, pickling, alcoholization and others.
In the method of cold storage (moderate cold), a temperature not lower than cryoscopic, at which freezing of a biological system begins, is used.The use of moderated cold facilitates retardation of biological processes that occur in raw materials and reduction in the activity of microorganisms, most of which develop at a temperature of 37 °С.
When decreasing a temperature, a reduction in the biological and biochemical activity in raw materials and microorganisms can be explained by dependency of a chemical reaction rate on a temperature and a decrease in microbial cytoplasmic membrane permeability.The method of cold storage gives an opportunity to preserve raw materials with minimal changes in its natural properties much longer than the biosis method.
Product freezing envisages their cooling to a temperature lower than cryoscopic.This preservation method consists in reduction of a biological system temperature lower than a point of its fluid freezing.The cryoscopic point depends on the concentration of soluble substances in the cellular fluid and on average is in a range from -0.6 °С to -1.2 °С for meat; -0.55 °С for milk; -0.5 °С for eggs; -0.6 °С to -2 °С for fish.Upon further reduction of a temperature, almost all free water freezes and the activity of microorganisms and enzymes virtually fully stops; as a result, it becomes possible to preserve initial quality of products for a long time provided that a temperature is constantly at an established level.
Основные требования, соблюдаемые при замораживании пищевого сырья и продуктов, формулируются следующим образом: formed simultaneously leading to formation of many small ice crystals in cells and the intercellular space even upon almost complete freezing, which cannot damage integrity of cellular membranes of product tissues.Therefore, the tissue structure changes only slightly during the following thawing.These products better retain their nutritional and organoleptic properties and their drip losses are insignificant.
Frozen food and raw materials can be preserved much longer than when using moderately reduced temperatures.This can be explained not only by the quantitative difference in the low temperature process of freezing and cold storage but also by the fact that in frozen foods the major part of moisture is transformed into the solid state.Therefore, microorganisms, which nutrition occur in the osmotic way, are deprived of the opportunity to use foods that contain small proportion of moisture in a liquid state.When using a method of raw material and food freezing, the principle of anabiosis is relevant (although not fully) only to microorganisms as the vegetative forms of microorganisms die at low temperatures, while spores survive transforming into the anabiotic state.At slow freezing, the number of survived microorganisms is higher than at fast freezing; however, many of survived microorganisms are damaged and later die.A degree of preservation of microbial life functions is influenced by a microbial species, their environment, rate and temperature of freezing and storage.Repeated freezing and thawing lead to a decrease in the viable microbial number.

Conditions and methods of food raw material and product freezing
In terms of duration, a freezing process can be characterized as slow (quiet), intensive and fast.These terms of freezing rate are rather conditional, and it is more convenient to regard a mean freezing rate as a ratio of distance that the front of free water ice formation covers in a product to duration of its passage in cm/h.It is possible to conditionally accept the following classification of the freezing character depending on the process rate: а) slow freezing at a rate of 0.1 to 1 cm/h; b) intensive (medium rate) freezing at a rate of 1 to 5 cm/h; c) fast freezing at a rate of 5 to 20 cm/h.
The main requirements that are met when freezing food raw materials and products are formulated as follows: Food raw material and product freezing can be carried out by several methods according to a refrigerant type: 1) by air -slow (quick), intensive and fast; 2) by a liquid phase (brine) -contact and non-contact (between cooled metal plates); 3) in contact with gas cooling agent having low boiling temperature.
Замораживание в жидкой среде производится в форме замораживания в рассоле.По способу, замораживание в рассоле, разделяется на две группы: а) контактное замораживание (продукт непосредственно соприкасается с рассолом); chamber.As a product freezes, the rate of heat transfer reduces; however, cooling is continued until establishment of a small difference between temperatures in a chamber and a refregerant that corresponds to the conditions of the thermal resistance of cooling surfaces.Air circulation accelerates freezing but also increases shrinkage losses in a product upon freezing; therefore, at low temperatures of freezing (an air temperature lower than -23 °С), when an effect of circulation on crystal formation is not high, air circulation in chambers is excluded with the aim of lowering shrinkage losses, excessive surface desiccation and evaporation of aromatic substances from a product.Freezing in a liquid medium is carried out in a form of freezing in brine.Freezing in brine is divided into two groups according to a method: а) contact freezing (product directly contact with brine); б) бесконтактное замораживание (продукт заключается в оболочки или формы, соприкасающиеся с рассолом).

Contact freezing exists in two forms: а) freezing by immersion b) freezing by spraying
Usually, aqueous sodium chloride solution serves as a cooling agent.The use of aqueous salt solutions of sodium potassium or magnesium is unacceptable as they impart a bitter taste to a product.Although both contact methods have advantages (the acceleration of the process and absence of weight losses), they also have two main disadvantages: а) salt penetration into a product to a certain depth; b) a color change that deteriorate apparent commercial product quality.Liquid freezing of food in brine began to be used in a primitive form for the first time at the end of the 19th century in the Russian fisheries (in mixtures of ice with salt) and later in a form of immersion of a product into a salt solution cooled by different cooling agents.During freezing by immersion, salt diffuse into a product because of the difference in the osmotic pressure of a salt solution and free moisture of a product even during freezing in a solution cooled to the cryoscopic point.However, in a saturated aqueous salt solution cooled to the cryoscopic point, an immersed product does not transfer moisture and does not absorb salt as the process of exchange diffusion based on the osmotic pressure differences does not occur in the product -cooling agent system.When a system temperature deviates from the cryosciopic point, a difference in the osmotic pressure appears and salting of a product begins.Impossibility to eliminate product salting is conditioned by a temperature difference between a product and cooling agent that arises during freezing.Near a surface of a freezable product, a cooling agent will always be warmer than its another part, even if its volume-averaged temperature is equal to cryosciopic.That is, salt osmotic diffusion [7] into a product will occur over the whole period of freezing.Since it is practically impossible to maintain a temperature of brine at a cryoscopic point (warming of a solution by a product, a decrease in heat transfer by cooling units due to ice deposition), product preliminary cooling is necessary, as well as addition into brine of substances that reduce a freezing temperature, for example, glycerol (each 5% of glycerol decrease a freezing temperature by 1°С lower than cryoscipic); however, a product gains a sweetish taste and a thin layer of brine remains on its surface leading to a product color change during storage.An amount and проникновения соли в продукт зависят не только от температуры замерзания рассола, но и от биохимических и физико-химических характеристик продукта.Поверхностный слой жира может почти полностью предотвратить просаливание продукта.Время замораживания при контактном способе при температуре рассола -23°...-25 °С составляет 6-8 часов.Замораживание контактным способом орошением рассолом, предполагает три фазы: а) предварительное обмывание продукта душем; б) замораживание продукта в среде тонко распыленного форсунками рассола; в) смыванием под душем капиллярного слоя рассола, осевшего на продукте.Если продукт имеет хорошо подготовленную и чистую поверхность, первая фаза необязательна.Распыление рассола, способствуя его испарению, повышает теплоотдачу.
If a product has a well prepared and clean surface, then the first phase is not necessary.Brine spraying facilitates its evaporation and increases heat transfer.
However, a process of freezing by spraying proceeds more slowly than freezing by immersion.At the same temperature of cooling brine, time of freezing by spraying is elongated approximately by 50%.Disadvantages of contact freezing in a liquid medium can be avoided by freezing a product in envelopes using a non-contact method.With that, salts (potassium chloride, magnesium chloride and others) with lower cryoscopic point than that of sodium chloride can be used in brines.
Non-contact freezing.To protect a product from an effect of brine, different brine impermeable envelopes are used.It is necessary to ensure maximum elimination of air between a product surface and an envelope.
Expansion of the pre-packed products as well as a necessity of convenient and fast freezing of small-sized products and their storage led to the use of the method of noncontact freezing between cooling metal plates.The main options of non-contact freezing between two plates can be presented in four types depending of a refrigerant, plate design and methods of cooling.If a refrigerant is air, the plate external side is made either smooth or riffle; if a refrigerant is brine, it can either flush a plate from an external side, or transit inside the latter.When cooling plates by direct evaporation, a refrigerant is evaporated inside plates.The time of freezing in plate freezers depends on a value of heat transfer coefficient between a refrigerant, a cooled surface of a plate and a product.Minimal freezing time is achieved when using either brine or an evaporating cooling agent as a refrigerant.The freezing process of products in packages is slowed down by thermal resistance of a packaging material and a presence of isolating air layers.The coefficient of heat conductivity for paper, cardboard and cellophane at a width of 0.05-0.1 mm is in a range of 0.1 to 0.84 J/m hour °С.During brine cooling, the coefficient of heat transfer depends on the brine flow rate in a unit.It was established experimentally [3] that the optimal rate of brine circulation is 0.2-0.3m/s as at higher rates, freezing time reduces quite insignificantly.
In plate freezing units, a pre-packed product usually is frozen in a package as it is extremely difficult to package a frozen product at low temperatures, and an increase in a temperature causes product thawing.An effect of heat resistance of packages and insulated air layers can be reduced to minimum by pressing packaged products due to a decrease of heat resistance of intermediate layers.Upon slight pressing of packaged products, removal of the air layer decreases condensate dropout between a product and package.The experiments of Ryutov D.G. and Khistodulo D.A. [8] demonstrated that a pressure on a product that contains free moisture should not exceed 0.1 kg/cm 2 in order to avoid жимания клеточного сока.Эксплуатация рассольных плиточных скороморозильных аппаратов осложнена коррозионной активностью рассольных систем, а аппаратов с испаряющимся хладагентом, сложностью полной герметичности непрерывно действующих систем.
Freezing with the use of an intermediate refrigerant is applied for freezing of single-piece products.Largely, these are air quick freezers of conveyor type, which represent heat-insulated box with an air cooler and conveyor inside, along which a product moves.Apparatuses are classed as tunnel, with belt-type multilevel conveyor and spiral.To reduce overall dimensions of tunnel apparatuses, a conveyor is made multilevel; a product is transferred to the top layer and falling to the next following lower layers moves inside an apparatus.Fluidization freezers used for freezing of small-sized products stand apart.In terms of design, they are similar to belt-type freezers but differ in a direction of supplied cold air; air is supplied from the bottom of a belt and a product is «floating» over a belt, which results in a uniform contact of a product and air flows.
Cryogenic apparatuses based on liquid nitrogen, which use multi-zone principle of action, characterize the modern trends in the development and use of quick-freezing technique.The multi-zone system ensures a decrease in nitrogen expenditure due to the use of cooling potential of gas nitrogen produced as a result of liquid nitrogen evaporation.Advantages of cryogenic freezing are low duration of the process, minimal shrinkage losses during freezing and ecological safety.The use of the cryogenic method allows bringing frozen product manufacture into proximity
The basis of the tunnel cryogenic apparatus design is three-zone scheme of freezing, which makes it possible to use nitrogen vapors after its evaporation in the freezing zone without preliminary cooling and temperature equalizing over a product volume.Product freezing is carried out due to liquid nitrogen supply through a system of nozzles into the freezing zone; gas nitrogen is directed to the zone of product preliminary cooling as well as to the zone of temperature equalizing using circulating axial-flow fans.Exhaust steam is removed using a system of ventilation skips installed from the side of product input.The main advantages of the nitrogen quick-freezing apparatuses compared to machine systems are: a) ecological purity; b) a 2-3 time decrease in capitalizable costs; c) high quality of a frozen product; d) minimal shrinkage of a product upon freezing; e) universality that allows working with different types of raw materials and products.

Peculiarities of freezing and storage of raw materials and products from animal protein
Protein and fat that contain all necessary nutrients are an ideal medium for microbial growth.Moreover, the fat tissue is susceptible to oxidation leading to rancidity and desiccation of the whole product mass.The shelf-life of raw materials and products from animal protein is extended upon retardation of volatile particle movement, weakening or slowing down the biological activity of components.This effect is achieved upon freezing.The bacterial growth is stopped at -8 °С, and at a temperature of -18 °С, the chemical activity and microbial activity are stopped.Ice crystals that are developed in a temperature range of 0...-5 °С, damage cell walls destructing a product tissue.Fast freezing reduces the risk of this destruction due to formation of small ice crystalline hydrates that do not have needle shape.A decrease in a temperature slows down the microbial activity, evaporation process and chemical reactions associated with oxidation.At a temperature of 0 °С and relative humidity of 85 %, lean meat can be stored approximately 21 day, while fat meat only 14 days.At a temperature of 5 °С, the duration is reduced to 1 day [11,12,13].An important factor that is associated with freshness is meat color.Different hues of red color are linked with the state of myoglobin oxidation.Fresh meat usually has дает оксимиоглобину ярко-вишневый цвет.В действительности оба состояния окисления безвредны, но потребителям больше нравится ярко-красный цвет.Поэтому упаковщики используют полимерные пленки, которые допускают проникновение безвредного количества кислорода, для создания привлекательного внешнего вида свежего мяса.

Особенности замораживания и хранения продукции мясо-растительного происхождения
Растительное сырье продолжает «дышать» и созревать в после урожайном периоде.Кроме того, оно содержит большое количество воды и вянет при из-purple red color because of a slight deficiency of oxygen.Treatment with an excessive amount of oxygen gives oxymioglobin a bright cherry red color.In fact, both oxidation states are harmful; however, consumers like more bright red color.Therefore, packagers use polymer films that allow penetration of safe quantity of oxygen for formation of attractive appearance of fresh meat.
The following problems arise upon freezing and storing meat raw materials: 1. Psychrophilic bacteria are present in meat raw materials.2. Animal fat (especially, back fat) easily oxidizes.3. Proteins of white chicken meat are not as stable as red meat proteins.The activity of psychrophilic bacteria is not affected by cooling to the same degree as that of the mesophilic types; therefore, the possibilities of hot meat storage are limited.To ensure control of psychrophilic bacteria, frozen white meat and mechanically deboned meat (MDM) are usually stored at lower temperatures (-30 °С) compared to other protein containing frozen meat raw materials and products.
Cold storage of protein products can cause ice sublimation and their serious desiccation, the so-called «cold burn».Tight packaging with a good barrier for humidity and minimal head space will reduce desiccation during storage.To avoid ice formation inside a package and product desiccation, it is necessary to fill a package fully.Packages for frozen meat products should be made of heat labile materials that maintain flexibility at freezing temperatures, provide protection from moisture and tightly fit a product.If cardboard is used as a package element, it should be richly paraffinized or covered with polyethylene to protect from moisture that is inevitably present in the process of freezing.A good example of frozen product packaging are PVC packages with good barrier properties, which are used for packaging and cold storage of poultry.After cutting, poultry is packed in packages and moves through a vacuum machine.As a result, a film tightly fits a product like a second skin.The impermeable barrier prevents water losses and «cold burn» for 30-45 days, as well as penetration of oxygen that oxidizes animal fats.

Методы размораживания пищевых продуктов
В настоящее время на пищевых предприятиях России применяется несколько способов размораживания, при которых теплоносителями являются воздух, паровоздушная среда, вода и рассол.Известны также способы размораживания с помощью ультразвука, инфракрасных лучей, электрического тока высокой, сверхвысокой и промышленной частоты и под вакуу-of biological and abiotic changes depends on a particular type of plant raw materials.Pea, green legumes and vegetables that have leaves «breathe» much faster that stems, tubers and roots.Potato, beet and carrot «breathe» more slowly; therefore, it is much easier to store them.Salad loses moisture much faster than beet due to a large surface area.Vegetable raw materials have an optimal ageing temperature (about 20 °С) and a threshold temperature lower than 5 °С, which prevents ageing.According to the empirical rule, a 10 °С decrease in a temperature increases shelf-life threefold (on condition that freezing is prevented) [9,10].Freezing of certain vegetable crops leads to destruction of the cell structure and after thawing they are spoiled very quickly.Ageing of vegetable crops is controlled by several ways.A «breath» rate can be reduced by decreasing an oxygen amount; however, a certain amount of oxygen should always be present for maintenance of the native condition of raw materials.Such technologies are used when packaging and storing in the modified gas atmosphere (MGA).Ethylene produced by plant tissues is associated with ageing of many types of plant raw materials and control of its content in a package is effectively used for retardation or acceleration of the ageing process.Starch containing raw materials are preserved over six month in an atmosphere that contains 5% of oxygen and 3 % of carbon dioxide (nitrogen accounts for the rest 92 %) [10], but in the absence of ethylene.These raw materials will be additionally aging if they are placed in conditions with the ethylene content at a level of several parts per million.Control of the storage atmosphere and temperature is a key condition for prolongation of plant raw material storage.At 90% humidity, a growth of bacteria and fungi increases.Moreover, sealed plastic packages (bags) are subjected to condensation and humidification.These factors complicate a problem of raw material and product storage.A compromise in many cases can be the use of perforated plastic envelopes or envelopes with holes.That allows a product to «breathe» upon a known risk of contamination and moisture loss.Another solution is a choice of film packaging materials with high gas permeability.
Available methods of thawing can be divided into three main groups.The first group includes the methods that use convection heating by heating media having different thermo-physical properties with different thermal gradients arising at their introduction.The second group consists of the thawing methods, which are based on heating by transformation of different types of energy into thermal energy directly in a processed product.These types of energy include the energy of electric field with different frequencies and the energy of ultrasonic vibrations.When using the energy of the alternating electric field, a homogeneous non-gradient heating of a product over the whole volume can be performed.The third group consists of the combined methods that use simultaneously convective and non-gradient heating.In a combined method of thawing, air, microwave, vacuum, electrical contact heating can be used among others.
In products of animal origin, an effect of tissue enzymes is manifested, mainly, by an increase in hydrolytic breakdown of proteins, as a result of which, favorable conditions for spoilage microflora are created.Microbiological processes occur in fast frozen meat after thawing almost with the same rate as in cooled meat at the same conditions of storage.Water vapor condensation upon thawing causes the accelerated development of microorganisms and, in slowly frozen meat, these processes proceed faster, which can be explained by higher enzyme activity in this meat.
For food products with the tissue structure (meat, fish, poultry), the most important indicator of reversibility of properties upon freezing is a value of drip loss.Drip losses are considered an external sign of protein substance denaturation.The main component of drip is water that was not absorbed by a product upon thawing as well as water that is released from a product under an effect of compressing when thawing.Drip losses can be accompanied by high losses of soluble substances -vitamins, enzymes, minerals, sarcoplasmic proteins and so on [15].
Drip losses in poultry depend on the muscle physiological state; at the moment of freezing they are maximal at the stage of rigor mortis and less significant at other stages.They also depend on freezing rate.Upon slow air freezing, losses increase 3 times compared to immersion method [15].
Drip losses during MDM thawing are subject to the same regularities as during meat thawing; however, as a rule, they are higher than in meat.A drip loss value depends on a MDM type and composition, the presence of bone fat in it, protein content, shape and size of frozen block and so on [15].
Quality of thawed plant raw materials depends on its type and storage conditions; in several cases, freezing methods have secondary significance.At the same time, it was established that for protein containing raw material, the most optimal method is dielectric thawing and the least optimal method is air thawing.In quality assessment of protein containing plant raw materials thawed by different methods, it was established that dielectrically thawed products were distinguished by higher content of intact raw materials, better consistency and less losses of vitamin C. The intensity of qualitative changes in thawed products is conditioned first of all by dynamics of microbiological and enzyme processes.Depending on many interacting factors, the activity of the latter can both increase and decrease.Storability of plant raw materials after thawing is less than that of animal products as they are less resistant to microbiological processes.Therefore, thawed meat-andplant products have to be maximally quickly used or realized due to rapid spoilage and deterioration of marketable appearance [10].
Analysis of different thawing methods shows that when using any heat transfer medium (air, water), process acceleration is limited.When thawing food product frozen in blocks for industrial purposes under the conventional accelerated technology of heating due to air convection or warming with water, product pollution and spoilage are possible.An improvement of the thawing technique is associated with changes in processing methods, a necessity of the further process intensification and development of интенсификации процесса, созданием конструкций агрегатов непрерывного действия.При этом важнейшим условием должно быть максимальное сохранение исходного качества продукта.
Analysis of available methods and an experience of foreign companies in using the microwave energy for food freezing demonstrated advantages of this method over others: saving of production space, strict regulation of the final temperature inside a product; simplicity of unit maintenance and a decrease in labor expenditures due to food thawing in packaging.Assessment of quality and sanitary condition of finished products showed that microwave thawing allows reducing losses of protein substances and vitamins, preventing microbial growth and improving meat tenderness, which is especially important in production of cooked sausages from thawed raw material.
A choice of a thawing method is conditioned by a capacity of an enterprise, its possibilities and a type of processed product.
In the world practice, an assortment of products that are preserved by fast freezing is extremely wide.Production of fast-frozen products in developed countries increases annually by 5-7 % [14].Production of such products is organized on the flow-type technological lines that include a process of fast single-piece freezing at the final stage.At present, more than 500 different world companies manufacture fast-frozen products.The USA, the Netherlands, France, Germany, Italy, Hungary and Poland occupy the leading place in production of such products.Unfortunately, up to now, the development of fast-frozen products manufacture in Russia has not achieved a desirable level in terms of assortment, production volumes and technological equipment.

Due to a necessity
to reduce product shrinkage losses, an air relative humidity in freezing chambers is maintained at a range of 85 % to 90-92%.Recently, fast freezing in special quick freezers with fast moving air having a low temperature and high relative humidity has becoming more widespread: products in these units are placed on conveyor belts in a layer with a low height or are hung in a form of small sized pieces.In belt-type fast freezers with air cooling[2], the freezing duration at a circulating air temperature of -50°...-60 °С and velocity of 5-6 m/s is 0.5-4 hours depending on a product thickness.This is confirmed by Rottenberg А.G.[3].To intensify a freezing process, it was suggested to use ejector air coolers[4, 5]  with a heat transfer coefficient of cooling elements increased by 2.5-3 times.Ejector air coolers are a system of pipelines with a directly evaporating cooling agent or brine that are intensively blown over by ejectors.The velocity of an air discharge from ejectors is about 20-30 m/s; with that, the freezing time of a meat half-carcass with a weight of 70 kg at an air temperature of -18°С is 40 hours.To reduce shrinkage losses and maintain product commercial quality during air freezing, different natural and artificial envelopes can be used.Preliminary packaging of a freezable product determines quality of its further storage in a frozen form.The use of frozen product glazing (2.5-3.0% of weight) increases product stability, reduces weight losses and preserve its quality during following cold storage.