Miscellanious

Good Practices for Preservation of Meat and Poultry Products

November 17, 2022

3341

Good Practices for Preservation of Meat and Poultry Products

Food preservation is a method of maintaining foods at a desired level of properties or nature for their maximum benefits. Preservation usually involves preventing the growth of bacteria, yeasts, fungi, and other micro-organisms (although some methods work by introducing bacteria, or fungi to the food), as well as retarding the oxidation of fats which cause rancidity. There are various methods of preservation chilling, freezing, curing, smoking, dehydration, canning, radiation preservation etc. Chilling is most widely used method for preservation for short term storage of meat because chilling or refrigeration slows down the microbial growth and enzymatic as well as chemical reactions. Freezing is the method of choice for the long term preservation of meat. It has advantage of retaining most of the nutritive value of meat during storage. Meat smoking was known to man as an aid in preservation for a long time. Smoke contains a large number of wood degradation products such as aldehydes, ketones, organic acids, and phenols etc. which exert bacteriostatic affect besides imparting characteristic smoky flavour. Canning is a process of preservation achieved by thermal sterilization of product held in hermetically sealed containers. Canning preserves the sensory attributes such as appearance, flavour and texture of the meat products to a large extent. Freeze drying of meat is a satisfactory process of dehydration preservation due to better reconstitution properties, nutritive quality and acceptability. It involves the removal of water from the frozen state to vapour state by keeping it under vacuum and giving a low heat treatment. Maintaining or creating nutritional value, texture and flavour is an important aspect of food preservation, although, historically, some methods drastically altered the character of the food being preserved. Meat and poultry products are chilled immediately after slaughter to acceptable internal temperatures which insure the prompt removal of the animal heat and preserve the wholesomeness of the products. As such, due to the recent up gradation of preservation techniques, the preservation industry is also growing almost at the same rate as the food industry which is about 10 to 12% per year.

Food, which contains essential nutrients, such as fats, proteins, carbohydrates, vitamins, and minerals, is the most indispensable part of human life. It is the basic necessity without which the survival of living beings is not feasible. Food is an edible substance of plant or animal origin, which is consumed to maintain life, provide energy and promote growth . Among all the industries in the world, food industry is the most prominent and fastest growing enterprise. In India, meat production was estimated 7.0 million tons in 2015-2016. Various technologies are being developed in order to meet the ever increasing demand of food due to population growth. Since ancient times, humans have employed several methods for preserving the food, so that they can store it to eat later on . The canning of vinegar was introduced in 1782 and the preservation of food by canning was patented by Nicolas Appert, a French Chemist. Later in 1837, Louis Pasteur, a French Scientist, used heat for the first time to destroy undesirable organisms in bear and wine. The use of sodium benzoate as a preservative in certain foods was given oficial sanction by USA in 1980. In the year 1990, the application of irradiation of the poultry was approved in the United States . Meat primarily obtained from herbivorous animals, such as cattle, buوٴaloes, goats, sheep, camels, horses, is widely consumed by people of developed as well as developing nations . Rich nutrient matrix meat is the first-choice source of animal protein for many people all over the world .According to the American Heart Association, the daily consumption of meat should be limited to six ounces . The transformation of animals into meat involves several operations, which include handling and loading of animals on the farm, transporting animals to slaughterhouses, oوٴ-loading and holding of animals and slaughtering of animals. Poor operational techniques and facilities in any of these operations will result in unnecessary suوٴering and injuries to animals, which can lead to loss of meat, reduced meat quality and spoilage of meat. Therefore, the prevention of contamination during meat cutting and processing is very essential . Storage time can be extended through hygienic slaughtering and clean handling of the carcass .Due to nearly neutral pH, high moisture content and rich nutrients, it is highly prone to contamination by microorganisms, which makes the preservation of meat more diٹcult than most other foods. The principle of preservation is to create unfavorable conditions for the growth of microorganisms, which result spoilage of food. Due to spoilage, the texture, flavor and nutritive value of meat are altered and thereby, rendering it inedible for human use. Unless proper preservation methods are adopted, deterioration, microbial activity, enzymatic and chemical reactions along with physical changes is bound to occur. However, once meat is contaminated with microorganisms, their removal is diٹcult. Hence, preservation of meat is done by various preserving techniques such as chilling/refrigeration, freezing, curing, smoking, thermal processing, canning, dehydration, irradiation, chemicals and pressure processing. This communication is an attempt to present an overview of various methods employed for the preservation of meat throughout the world.

Preservation of Meat

Meat preservation became essential for transportation of meat for long distances without spoiling of texture, color and nutritional value aіer the development and rapid growth of super markets . Traditional methods of meat preservation such as drying, smoking, brining, fermentation, refrigeration and canning have been replaced by new preservation techniques such as chemical, bio-preservative and non-thermal techniques . The aims of preservation methods are to inhibit the microbial spoilage and also to minimize the oxidation and enzymatic spoilage. Current meat preservation methods are broadly categorized into three methods (a) controlling temperature (b) controlling water activity (c) use of chemical or bio-preservatives . A combination of these preservation techniques can be used to diminish the process of spoilage .The preservation of food has several objectives :

1. To control foodborne infections and intoxications 2. To ensure the safety of food from microbes 3. To prevent the spoilage of food 4. To extend the shelf life of food 5. To enhance the keeping quality of food 6. To reduce financial losses.

Chilling/refrigeration

This is the most widely used method of preservation for short term storage of meat as chilling/refrigeration slows or limit the spoilage rate at temperature below the optimal range can inhibit the microbial growth , enzymatic as well as chemical reactions . Storage of fresh meat is done at a refrigeration temperature of 2 to 5°C. Chilling is critical for meat hygiene, safety, shelf life, appearance and nutritional quality . Carcasses are first hanged in chilled coolers (15°C) to remove their body heat, and are then passed on to holding coolers (5°C). It is essential to maintain proper spacing between carcasses so as to allow throughout air circulation. It is employed by two methods: (a) immersion chilling, in which the product is immersed in chilled (4°C) water and (b) air chilling, in which the carcasses are misted with water in a room with circulating chilled air . Refrigeration of meat begins with the chilling of animal carcass and continues throughout the entire channels of holding, cutting, transportation, retail, display and even in the customer household before the ultimate use. Нe relative humidity is generally kept at 90% in order to avoid excessive shrinkage due to loss of moisture. The refrigerated storage life of meat is influenced by species of origin, initial microbial load, packaging and temperature as well as humidity condition during storage. Pork and poultry starts with comparatively high microbial load. Irrespective of species of origin, maximum care should be taken during handling of meat in order to check further microbial contamination. Refrigerated temperature favors the growth of psychrophilic organisms causing spoilage of meat in due course of time. Generally, fresh meat remains in good condition for a period of 5-7 days if kept at refrigerated temperature of 4 ± 1°C. Cold-shortening and toughening may result from ultra-rapid chilling of pre-rigor meat . It is emphasized that the processed meat should be stored under refrigerated condition till they are finally consumed. The well preserved meat has enhanced shelf life as compared to fresh meat.

Freezing

is an ideal method of keeping the original characteristics of fresh meat. Meat contains about 50-75% by weight water, depending on the species, and the process of freezing converts most of water into ice . It stops the microbial load and retards the action of enzymes. The most significant advantage of freezing is the retention of most of the nutritive value of meat during storage, with a very little loss of nutrients occurring in the drip during thawing process. It is important to wrap fresh meat in suitable packaging film before freezing otherwise meat undergoes freeze burn. This abnormal condition occurs due to progressive surface dehydration resulting in the concentration of meat pigments on the surface. The quality of frozen meat is also influenced by its freezing rate. In slow freezing, there is formation of large ice crystals, which may cause physical damage to muscular tissue, giving it distorted appearance in the frozen state. In fast freezing, numerous small ice crystals are formed uniformly throughout the meat tissue. The freezing rate is increased with decreases in temperature, almost 98% of water freezes at -20°C and complete crystal formation occurs at 65°C .Thus, problem of muscle fiber shrinkage and distorted appearance is not there in meat tissue. The drip losses during thawing are considerably low as water freezes within the muscle fiber itself. Numerous small ice crystals on the surface of the fast frozen meat are also important as they give a desirable light color as compared to slow frozen meat. Microbial growth stops at -12°C and total inhibition of the cellular metabolism in animal tissues occurs below -18°C . However, enzymatic reactions, oxidative rancidity and ice crystallization will still play an important part in spoilage . During freezing, about 60% of the viable microbial population dies but the remaining population gradually increases during frozen storage.

Curing

Sodium chloride, sodium nitrate, sodium nitrite and sugar are main curing ingredients. Various methods of curing are practiced in India, such as dry cure, pickle cure, injection cure, direct cure etc. Preservation of meat by heavy salting is an old age practice. Sodium chloride has a long history of use in food preservation in suٹciently high concentrations . It was applied as a thumb rule because refrigeration facilities were not available during olden days. Later, curing by common salt and sodium nitrate resulted in comparatively improved products. Sodium Chloride inhibits microbial growth by increasing osmotic pressure as well as decreasing the water activity in the micro-environment .Some bacteria can be inhibited by concentrations as low as 2% . A concentration of 20% of sodium chloride is high enough to inhibit many food spoilage yeasts including Debaryomyces hansenii, Yarrowia lipolytica, Kloeckera apiculata, Kluyveromyces marxianus, Pichia anomala, Pichia membranaefaciens, Saccharomyces cerevisiae, Yarrowia lipolytica, Zygosaccharomyces bailii, and Zygosaccharomyces rouxii . However, some microorganisms from the genera Bacillus and Micrococcus have shown ability to tolerant high concentrations of salt .Sugars have the capabilities to bind with moisture and reduce water activity in foods . Dextrose, sucrose, brown sugar, corn syrup, lactose, honey, molasses, maltodextrins, and starches are generally used in dried meat processing as a source of sugars or carbohydrates to enhance flavor, reduce harshness of salt and lower water activity . In Canada and the United States, sugars are generally recognized as safe .The nitrites used in meat preservation industry are always in the form of salts such as sodium nitrite or potassium nitrite. Nitrites provide stabilized red meat color, cured meat flavor and rancidity retardation .Further, nitrite salts are eوٴective in controlling color, lipid oxidation and odor in addition to controlling the anaerobic bacteria .The current limit for nitrite in food is 156 ppm in US, and 200 ppm in Canada for meat products . On the other hand, the use of nitrite as food additive may form carcinogenic nitrosamines with prolonged exposure. However, there is no epidemiological evidence to support the relationship between nitrate consumption and a specific cancer or cancer risk.

Smoking

Meat smoking is also known as an aid in the preservation for a long time to the meat product. It is now well known that smoke contains a large number of wood degradation products such as aldehydes, ketones, organic acids, phenols and many more. Preservation of meat by smoke is also due to surface dehydration, lowering the surface pH and antioxidant property of smoke constituents. Curing and smoking of meat are closely related. Нese days, curing is usually followed by smoking. Smoke is produced in specially constructed smoke house where sawdust or hard wood and sometimes both are subjected to combustion at the temperature of about 300°C . Smoke generation is accompanied by formation of numerous organic compounds and their condensation products. Aldehydes and phenols condense, which constitute 50% of smoke components and contribute to the most of the color of the smoked meat products. Phenols act mainly as the chief bactericidal compounds. Currently, many liquid smoke preparations are commercially available in the developed countries. Liquid smoke is generally prepared from hard wood wherein polycyclic-hydrocarbons are removed by filtration. Application of liquid smoke on the product surface before cooking imparts it a smoky flavor, which is very much liked by the consumer.

Thermal processing

Thermal processing as a preservative method is employed to kill the spoilage causing microorganisms. Pasteurization refers to moderate heating in the temperature range of 58-75°C, which is also the cooking temperature range of most of the processed meats. Нis heat treatment extends the shelf life of meat significantly. It is imperative that such products also need to be stored under refrigerated conditions. Sterilization refers to the severe heating of meat at the temperatures above 100°C whereby all spoilage causing microbes in meat are killed or their microbial cells are damaged beyond repair. Нis heat treatment renders the meat product commercial sterilization as the bacterial spores may still survive. However, exposure of meat to high temperatures imparts sulѓydryl flavors in cans and also modifies texture. Various meat products diوٴer in water content, fat and consistency. Нese are the deciding factors of thermal processing schedule. For example moist heat is more eوٴective in killing microorganisms and spores as compared to dry heat. Нerefore, a meat product with high moisture content requires comparatively less heat for sterilization.

Canning

It is the process of preservation achieved by thermal sterilization of a product held in hermetically sealed containers. Canning preserves the sensory attribute such as appearance, flavor and texture of the meat products to a large extent. Besides, canned meat products have a shelf life of at least two years at ambient temperature. Canning involves several steps, which include preparation of meat, precooking, filling, exhausting, seaming, thermal processing, cooling, and storage .

Dehydration

Removal of water from meat concentrate, the water soluble nutrients making them unavailable to the microorganisms. Нe extent of unavailability of water to microbial cell is expressed as water activity. Dehydration lowers the water activity considerably to prevent the growth of spoilage causing microbes. Sun drying of meat chunks as a means of preservation was practiced in ancient days but rehydration of such meat chunks used to be limited. Нe mechanical drying process involves the passage of hot air with controlled humidity but here also there is diٹculty in rehydration. Freeze drying of meat is a satisfactory process of dehydration, preservation due to better reconstitution properties, nutritive quality and acceptability of the meat products. Freeze drying involves the removal of water from a food by sublimation from the frozen state to vapor state by keeping it under vacuum and giving a low heat treatment. Freeze drying of meat is carried out in three steps, namely pre-freezing, primary drying and secondary drying [1]. Meat is first frozen at -40°C, and then it is dried under vacuum for 9-12 hours at low temperature in plate heat exchangers at 1-1.5 mm pressure of Hg. Ice crystals get sublimated to water vapors and there is no rise of temperature. In the 1st phase of drying, free and immobilized water of meat, which is freezable and constitutes about 90-95% of total moisture, is removed. Secondary drying is done at high temperature to remove remaining 4-8% bound water. Freeze dried products are packed under vacuum and have very good storage stability. The process has been largely used for the preparation of dehydrate meat soup mixtures.

Irradiation

Irradiation is also known as “cold sterilization”. It is the emission and propagation of energy in the material media. Electromagnetic radiations are in the form of continuous waves. Нese are capable of ionizing molecules in their path. Нese radiations can destroy the microorganisms by fragmenting their DNA molecules and causing ionization of water within microorganisms. It is pertinent to mention that microbial destruction of foods take place without significantly rising the temperature of the food [1]. Gamma radiations produce desired eوٴect only during food irradiation and have no eوٴect aіer removal of source. Нese are widely used in food preservation. Among the known ionizing radiations, UV radiations are mostly bactericidal in nature but do not have good preventing power, so these are used only for surface sterilization of meat.

Chemicals

Energy intensive freezing operations are the greatest way to preserve carcass, meat and meat products for a longer time, which inhibits bacterial growth, but not the psychrophiles and the spores. Most of these survive freezing and grow during thawing . Traditional methods for preservation of meat by salting and picking are well accepted procedures. Other chemicals have been used as food additives for preservation of meat but every country has drawn its rules and regulations and established limits for the purpose of prevention of harmful eوٴects to humans . Freeze storage cannot prevent oxidative spoilage and microbial/enzymatic spoilage .Thus, chemical preservation methods are quite beneficial in combination with refrigeration in order to optimize stability, product quality while maintain freshness and nutritional value . Antimicrobial preservatives are substances which are used to extend the shelf life of meat by reducing microbial proliferation during slaughtering, transportation, processing and storage . Growth of bacteria and spoilage of meat is depending on the species of bacteria, nutrients availability, pH, temperature, moisture and gaseous atmosphere . Antimicrobial compounds added during processing should not be used as a substitute for poor processing conditions or to cover up an already spoiled product .They oوٴer a good protection for meat in combination with refrigeration. Common antimicrobial compounds include: chlorides, nitrites, sulfides and organic acids . Freeze storage cannot prevent oxidative spoilage and microbial/enzymatic spoilage . Thus, chemical preservation methods are quite beneficial in combination with refrigeration in order to optimize stability, product quality while maintain freshness and nutritional value . Several organic acids have been generally recognized as safe. Benzoic acid, citric acid, propionic acid, sorbic acid and their salts are eوٴective mold inhibitors. Acetic acid and lactic acid prevent the bacterial growth whereas sorbate and acetate are capable of arresting the growth of yeasts in food. Ascorbic acid (vitamin C), sodium ascorbate and D-isoascorbate (erythorbate) have been used as meat preservatives. Their antioxidant properties can oxidize reactive oxygen species producing water. Ascorbic acid has been shown to enhance antimicrobial activity of sulfites and nitrites .The enhanced activities include both the antioxidant properties and the sequestering of iron . Benzoic acid and sodium benzoate are also used as preservatives in the meat industry. Нe un-dissociated molecule of benzoic acid is responsible for its antibacterial activity .The benzoic acid is generally used to inhibit yeasts and fungi rather than bacteria . It has been reported that yeasts such as Saccharomyces and Zygosaccharomyces have intrinsic ability to resist benzoic acid under the tolerable toxicological limits. Нe combination of benzoic acid treatment and nitrogen starvation conditions is suggested to enforce eوٴective food preservation from yeast spoilage.

Hydrostatic pressure processing

High pressure directly aوٴects cellular physiology of the microorganisms. High pressure of a few hundred MPa can decrease the viability of bacterial cells, and a pressure of a few tens MPa can decrease the growth rate. New high-pressure technology for food sterilization is being developed based on these facts. Нe inactivation is due to widespread damages of micro-organisms through modification of morphology and of several vulnerable components such as cell membranes, ribosomes, and enzymes, including those involved in the replication and transcriptions of DNA . Microbial inactivation through high pressure application has been well reviewed by &heіel . The extent of inactivation depends on several parameters such as the type of micro-organisms, the pressure level, the process temperature and time, and the pH and composition of the food or the dispersion medium. In general, Gram-negative bacteria such as Yersinia enterocollitica and Salmonella spp. were found to be more sensitive than Gram-positive bacteria such as Listeria monocytogenese and Staphylococcus aureus. Some strains of Escherichia coli O157:H7 were found to be relatively resistant to pressure. Some investigators reported the eوٴect of substrate on pressure resistance of S. aureus, S. enteridis and one of the resistant E. coli O157:H7 strains .There was greater survival of E. coli and S. enteritidis in ultra-high-temperature treated (UHT) milk compared to poultry meat, whereas there was greater recovery of S. aureus in poultry meat than in the milk. Нe simultaneous applications of pressure with mild heating (up to 60°C) significantly increased the death of E. coli O157:H7 in poultry meat and UHT milk compared to either treatment alone. In practical meaning, high-pressure processing is preferable as an additional final processing step to produce safety products. Highpressure processing can eliminate manufacturing contamination of Salmonella, Listeria monocytogenes, and other food-borne pathogens in finished, packaged products without any adverse eوٴects on color, flavor, texture, and moisture, and increase refrigerated shelf life. The tenderization of meat or acceleration of meat conditioning could be induced by high-pressure treatment and the improvement of thermal gel formability of pressurized actomyosin, especially at low salt concentration, opens up the possibility for exploitation of new types of meat products. The shelf life of cooked meat products prepared by conventional methods could be extended by exposing them to high pressure.

Hydrodynamic pressure processing

Tenderness is the major criterion driving consumer’s decisions to purchase meat. A means of controlling and assuring a meat product’s safety and tenderness level is essential. Unfortunately, tenderness has proven to be the most diٹcult quality factor for meat producers and meat packers to manage. Thus, a commercial method to ensure a consistently tender meat product is of primary importance for enhanced consumer acceptance of meat. Techniques applied individually or in combination include mechanical, chemical, temperature conditioning, aging, electrical stimulation, high pressure heat treatments, and alternative carcass positioning. A number of these techniques require additional holding periods, space, and labor. Furthermore, several of these methods have been criticized for their lack of consistency in tenderizing meat. Нe concept of tenderizing meat using shock waves from underwater detonation of explosives, called hydrodynamic pressure processing (HDP), was first patented by Godfrey . Hydrodynamics refers to the motion of fluids and the forces acting on solid bodies immersed in these fluids. Нe HDP process should not be confused with research using high hydrostatic pressure (HHP), which was introduced by Japanese scientists and dates back to the end of the 19th century. Нe HDP-treated meat displayed no outward signs of change, but on cooking, it was found to be significantly tender than non-treated control samples. HDP involves underwater detonation of a high-energy explosive in a containment vessel to generate a shock wave pressure front at velocities exceeding the speed of sound. Нe shock wave passes through the liquid medium and vacuum-packaged meat (placed at the bottom of the container). Shock waves generated and transmitted through water move equidistant from an explosive source depending on the shape of the explosive .The shock wave, with targeted pressure fronts of 70 MPa to 100 MPa in the HDP process, occurs in fractions of milliseconds. Hugoniot (adiabatic) compression of water (or of aqueous solutions) causes a temperature increase of only 2 to 3°C per 100 MPa, depending on the initial temperature and the rate of pressure increase . Pressure release causes a decrease in temperature of the same order of magnitude. Because the dynamics of the shock wave pressure front in the HDP process occur in fractions of milliseconds and at pressures less than 100 MPa, there is virtually no increase in the temperature of the meat or water. The shelf life of HDP-treated meat products is increased by reducing the non-pathogenic (normal) microbial flora in the sample. Microbial populations of HDP-treated meat does not increase significantly for approximately 14-15 days of storage at 5°C whereas there is increase in microbial population of untreated meat products.

Frozen techniques for Meat Products

Meat products are rich in protein, fat, water, and other nutrients and are considered essential for human growth, which is easily spoiled due to microbial deterioration during storage. Among all animal sources, both beef and chicken are the main meat protein sources and are popularly consumed in many countries. Beef, lamb/mutton, and chicken are the meat products that are produced worldwide in the greatest quantities majority of the research in the meat science discipline has the main focus on these species.

The global demand for meat products has increased during the recent COVID-19 pandemic, which means that a frozen meat product has become more lucrative. The global production of frozen food has expanded at a significant rate in recent years. The production and consumption of quick-frozen food in the world display a growth rate of 20%–30%. It is expected that frozen food will become the fastest-growing food in the world with its sales volume accounting for 60%–70% of all food in developed countries. In order to ensure the safety and economy of largescale production of meat products in the industry, frozen storage is still the most commonly used preservation method for meat products enterprises in the world. As global trade increases and the distance between producer and consumer expand, there is a great demand to freeze meat for transportation. Meat freezing is a practice to extend its shelf-life. The most improvements in freezing technologies have occurred in the past century but the commercial application of the freezing process is still disputed, however, even though scientific research indicates that they lead to an increase in the quality of meat.

FREEZING: Freezing of meat involves the reduction of the internal temperature of meat below its freezing point of -18 ⁰ C and further storing it at temperatures of less than its freezing point. Beef quarters will be accepted for freezing at a temperature, not above +4 ⁰ C and frozen within 36 hours to an internal temperature of -4 ⁰ C or below. Frozen storage for beef must be at a temperature of -18 ⁰ C. The meat must be wrapped in a polythene pack of at least 0.05 mm thickness and in stockinet. The form of wrapping greatly affects the freezing time; if it is loose, the pockets of air or cartons act as insulation and thereby increase freezing times. Wrapping in moisture-proof packaging can offset water losses. The shelf-life of meat is generally determined by appearance, texture, flavor, color, microbial activity, and nutritive value. All of these parameters are influenced by freezing, frozen storage, and subsequent thawing.

METHODS OF FREEZING

Slow freezing: Freezing undertaken in a cabinet freezer is essentially a slow process and is referred to as slow freezing. Slow freezing generally takes about 72 hours. The delay involved in slow freezing usually results in greater drip loss, during thawing than that associated with quick- freezing. The temperature of the product being frozen remains near the initial freezing point for an extended time. This results in the formation of a continuous freezing boundary and freezing proceeds slowly from the exterior to the interior. Extracellular water freezes more rapidly than intracellular water due to its lesser solute concentration. It favors the formation of pure ice crystals and the concentration of solutes in unfrozen conditions. Long periods of crystallization exist in slow freezing, producing numerous large extracellular masses of ice crystals that are easily lost as drip during thawing. Slow freezing also might result in mechanical damage to muscles, due to volume changes, associated with the formation of large ice crystals and concomitant shrinkage of muscle fibers that have lost water to extracellular pools.

Quick freezing: Quick freezing can also be achieved by Liquid Immersion Liquid spray and Cryogenic Freezing. The temperature of the product being frozen falls below the initial freezing point rapidly in case of quick freezing. It causes the spontaneous formation of numerous small ice crystals, resulting in a discontinuous freezing boundary and very little translocation of water. Most of the water inside the muscle fiber freezes intracellularly, so drip losses during thawing are considerably lower than in slowly frozen meat. Muscle fiber shrinkage and distortion are minimized than in slowly frozen meat. Volume changes are less and periods of crystallization are shorter than in slowly frozen meat and consequently, mechanical damage is correspondingly less. Smaller and more numerous ice crystals formed in quick-freezing reflect more light from meat surfaces, resulting in a lighter color than in slowly frozen meat.

PHYSICO-CHEMICAL CHANGES DURING FROZEN STORAGE OF MEAT

Frozen storage is one of the main storage methods for meat products. It is a form of low-temperature dehydration. However, it has been shown that even under ideal frozen stored conditions a certain amount of deterioration in the quality of meat so not uncommon. The available meats at retail markets should be of stable quality and free from pathogenic bacteria and fungi which can cause serious human diseases. Fresh meats are often treated by cooling or freezing to increase their shelf-life. Freezing and refrigeration processes are the common methods used to protect foods by preventing the microorganism growth that causes food-borne illnesses. Freezing and thawing mainly influence the water fraction of meat. Freezing reduces the water activity as well as enzyme activity of all foods and thus delays or avoids spoilage, prolongs storage life while retaining the original flavor, and reduces the loss of nutrients.

The oxidative spoilage will have occurred even at very low freezing temperatures, which resulted in the deterioration of the meat quality, including flavor, odor, color, etc. During the freezing of meat products, the formation of large and irregular ice crystals can destroy cellular integrity, resulting in the degradation of meat muscle tissue. Before frozen meat is processed, it needs to be thawed. The physical state of the muscle plasma (globulin and albumen proteins) is considerably altered. The protein structure of the meat is damaged during thawing, which is characterized by the damage of water holding capacity, tenderness, color, and texture characteristics of meat products. In the thawing process, the ice crystals formed in the freezing process melt, and the water produced cannot be fully absorbed, resulting in drip loss. The drip loss of meat products is directly or indirectly related to its color, freshness, and other physical and chemical indexes, resulting in the decline of its quality. The amount of drip loss is directly related to the thawing process, so the control of the thawing process also plays an important role in the quality of frozen meat products.

THAWING OF FROZEN MEAT: Thawing or defrosting frozen meat is usually done before cooking. It is usually necessary to take freezing to keep it at a low temperature, and then thaw before further processing. This is done in order to bring the meat to room temperature. Defrosting may be achieved in many ways, viz., Slow defrosting in a refrigerator or in cold air At room temperature in a rack or warm air In circulating cold water and Quick de-frosting in warm water or cooked without prior thawing. Defrosted meat is cooked in the same way as fresh meat.

Meat when thawed sometimes produces a watery fluid called “Weep or Drip”. This fluid mainly consists of water, salts. Due to the presence of large ice crystals in muscle, protein is also to some extent unable to reabsorb the entire water when the meat is thawed. Meats are considered a potential medium for microbial growth owing to their rich sources of proteins and high nutritional value. Thawed meat is liable to spoil more quickly than fresh meat. As the shelf life of the thawed meat is low, re-freezing of such thawed meat will materially yield meat of poor stability. The microorganisms do not grow faster on thawed meat than on fresh meat. Therefore, frozen meat should not be thawed too long before cooking. Meat, which has a high pH prior to freezing, has a low drip when thawed.

An understanding of the changes that freezing and thawing perpetuate in different meat types and cuts is essential to the meat industry, as their main objective is to produce superior products with high resale values that are both appealing and enjoyable to the consumer.

PRECAUTIONS FOR EFFICIENT CHILLING AND FREEZING OF MEAT:

To ensure chilling and freezing is efficient and delivers a consistently excellent product: The initial design of refrigeration space should take into consideration – product tenderness, weight loss, the possibility of spoilage, size of individual units, space required, rail height, wall, and floor surfaces. Temperature and relative humidity must be maintained at recommended levels constantly, and must be monitored regularly. Overloading must be avoided and carcasses must not touch each other. Door opening and closing must be kept to a minimum and access must be restricted to authorized personnel only. Adequate airflow around carcasses is essential. Carcasses of different species must not occupy the same area. Drip pans must be placed under carcasses and meat. Cold shortening must be avoided by delaying chilling to less than 10⁰C, 10 hours after slaughter.

METHODS FOR DEFROSTING FROZEN MEAT AND POULTRY.

Meat should not be defrosted on a counter-top at room temperature because the outside portion of the meat becomes warm, allowing microbes to begin to grow while the center portion of the meat is still frozen.

There are three safe ways to defrost beef: in the refrigerator, in cold water, and in the microwave. Never defrost on the counter or in other locations.

Refrigerator: The safest way to thaw meat is to remove in from the freezer and place it in the refrigerator. It should be put on a plate or pan to collect any juices that leak from the package. Ground meats, stew meat, steaks and chops may defrosted within a day. Bone-in parts and whole roasts may take 2 days or longer. Once the raw meat defrosts, it will be safe in the refrigerator for 3 to 5 days before cooking. Once the raw poultry thaws, it can be kept in the refrigerator an additional day or two before cooking. During this time, if you decide not to use the meat or poultry, you can safely refreeze it without cooking it first.
Cold Water:To defrost in cold water, do not remove packaging. Be sure the package is airtight or put it into a leak proof bag. Submerge the beef in cold water, changing the water every 30 minutes so that it continues to thaw. Small packages may defrost in an hour or less; a 3- to 4-pound roast may take 2 to 3 hours.
Microwave:When microwave defrosting plan to cook it immediately after thawing because some areas of the food may become warm and begin to cook during microwaving. Holding partially-cooked food is not recommended because any bacteria present wouldn’t have been destroyed.Foods defrosted in the microwave or by the cold water method should be cooked before refreezing because they may have been held at temperatures above 40 °F (4.4 °C).
It is safe to cook from frozen in the oven, on the stove, or grill without defrosting it first; the cooking time may be about 50% longer.

Once meat has been thawed, there is nothing wrong with refreezing it, providing the temperature of the defrosted product has not risen above 40°F and the length of time does not exceed recommended storage times. Refreezing meat will not necessarily reduce palatability. However, meat that is unwrapped and thawed, then re-wrapped and refrozen, may be slightly drier because of moisture loss. Meat is best thawed unopened, in its freezer packaging.