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.