Principles of preservation

• Removal of microorganisms or inactivating them
• Inactivating enzymes
• Removal of insects and worms

Various Preservation methods

1. 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.

Blanching refers to the process whereby the ingredients are covered with cold water and brought to a boil. As soon as the water comes to a boil, the impurities are skimmed from the surface and the murky water is drained.

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. This heat treatment renders the meat product commercial sterilization as the bacterial spores may still survive. However, exposure of meat to high temperatures imparts sulfhydryl flavors in cans and also modifies texture.

Various meat products differ in water content, fat and consistency. These are the deciding factors of thermal processing schedule. For example moist heat is more effective in killing microorganisms and spores as compared to dry heat. Нerefore, a meat product with high moisture content requires comparatively less heat for sterilization.

2. Chilling

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 .

3. Refrigeration

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. The relative humidity is generally kept at 90% in order to avoid excessive shrinkage due to loss of moisture. Нe 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.

4. Freezing

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. 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. And 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.

5. Drying

Removal of water from meat concentrate, the water soluble nutrients making them unavailable to the microorganisms. The extent of unavailability of water to microbial cell is expressed as water activity. Drying lowers the water activity considerably to prevent the growth of spoilage causing microbes. The mechanical drying process involves the passage of hot air with controlled humidity but here also there is difficulty in rehydration.

Freeze drying of meat is a satisfactory process of dehydration. It 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. 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. Then, 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.

6. 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. These radiations can destroy the microorganisms by fragmenting their DNA molecules and causing ionization of water within microorganisms. Gamma radiations produce desired effect only during food irradiation and have no effect after removal of source. These 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.

7. Curing

Sodium chloride, sodium nitrate, sodium nitrite and sugar are main curing ingredients.

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 Pichia anomala, Pichia membranaefaciens, Saccharomyces cerevisiae, Yarrowia lipolytica, Zygosaccharomyces bailii, Zygosaccharomyces rouxii etc.However, some microorganisms from the genera Bacillus and Micrococcus have shown ability to tolerant high concentrations of salt.

Sugars are also used as they 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.

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 effective in controlling color, lipid oxidation and odor in addition to controlling the anaerobic bacteria.

8. Smoke

Preservation of meat by smoke is also due to surface dehydration, lowering the surface pH and antioxidant property of smoke constituents. Smoke contains a large number of wood degradation products such as aldehydes, ketones, organic acids, phenols and many more. Meat smoking is an aid in the preservation for a long time to the meat product.

9. 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.

10. Chemical method

Chemicals have been used as food additives for preservation of meat as per the rules and regulations. Also, there are established limits for the purpose of prevention of harmful effects. For example: Formaldehyde is prohibited, since it is demonstrably toxin, but is permitted up to 5ppm. 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.

There are many chemicals, which prevent microbial growth in foods and act as preservatives. Several organic acids have been Generally Recognized As Safe (GRAS)for use as chemical preservatives. Fresh meat, when in the intact carcass, is not usually severely contaminated. On the other, in preparing products containing comminuted or minced meats, there is every possibility for massive bacterial contamination from the hands of operatives or from equipment. Hence, chemical preservatives were particularly employed in relation to meat.

Various essential oils have preservation properties and have been used to extend the storage life of meat products. These include eugenol in cloves and alkyl isothiocyanate in mustard seed and 0.3 percent of sage or rosemary was inhibitory and 0.5 percent bactericidal.

Benzoic acid and sodium benzoate are also used as preservatives in the meat industry. The un-dissociated molecule of benzoic acid is responsible for its antibacterial activity.

Ascorbic acid has been shown to enhance antimicrobial activity of sulfites and nitrites.

Acetic acid and lactic acid prevent the bacterial growth whereas sorbate and acetate are capable of arresting the growth of yeasts in food.

Chemically preserved meat items can be kept for a fairly long time even after opening the seal of the bottle. It is however essential to control their indiscriminate use for avoiding harmful efffects.