The preservation of fresh meat has been practiced since time immemorial. However, Nicolas Appert of France was the first person to attempt it scientifically in 1810 as he developed canning method, which was patented later. Preservation of food is done in times of plenty to make its use in times of scarcity. The main aim of meat preservation is to check meat spoilage, which causes some changes in texture, flavour, and odour of meat and finally loss of its wholesomeness. There are a number of methods that are used for keeping meat safe by controlling the growth of bacteria and mold.
VARIOUS METHODS OF MEAT PRESERVATION
1. Drying,
2. Low Temperature Preservation,
3. High-Temperature Preservation or Thermal Processing,
4. Curing and Smoking,
5. Antibiotics and Bacteriocins,
6. Fermentation,
7. Packaging,
8. Irradiation,
9. Hurdle Technology.
DRYING METHOD
Drying has the distinction of being the first and simplest method that has been adopted for the preservation of meat since antiquity. Drying refers to the removal of moisture (reduction in aw*) from the food. It is known that microorganisms and enzymes require adequate water in food for their sustenance. When moisture is removed from the food (during drying process), the activity of microorganisms and enzymes is Inhibited and the shelf-life of the product enhanced at ambient temperature. This method has some public health problems as there is likelihood of getting meat contamination with Salmonella organisms during the process of handling, preparation, storage and the viability of the pathogen in the contaminated product has been reported for more than six months.
LOW TEMPERATURE PRESERVATION
Low temperature preserves the food material by retarding the microbial growth, enzymatic and the chemical reactions that deteriorate the meat and cause spoilage. The most widely used methods based on this principle of preservation by low temperatures are refrigeration (chilling or icing) and freezing.
1.CHILLING
Refrigeration(chilling) refers to preservation by lowering the temperature of the meat to a point above the freezing temperature. Chilling is also widely used for short-term preservation of meat as it has no adverse affect on appearance., flavour and nutritive value.Meat carcasses are normally chilled / refrigerated immediately after the slaughter at about – 1°C, usually in the dark to avoid the oxidation of fat. In the presence of 10 per cent Carbon dioxide, the storage life of the meat is further increased because the growth of molds is inhibited.
2.FREEZING
At chill temperature the meat is cooled to 2°C. Meat starts freezing at -1 .5°C.Freezing aims at preventing the multiplication of harmful bacteria, molds and yeast as water is converted to ice and therefore, remains no longer available for microbes. Freezing occurs at different rates in different parts of the material being frozen. The rate is faster at some points, for instance on the surface, while in the deeper parts of the material there is a point at which cooling is slowest. This point is known as the ‘thermal center’. About half of the water is frozen to ice at -2.5°C. Three quarters of it are frozen at -7°C and some water still remains intact at -18°C. Then, the meat is further cooled to its storage temperature (- 18 to -20 or -30°C) until its thermal center reaches the storage temperature.
HIGH TEMPERATURE PRESERVATION
All living things are destroyed by heat where temperature is high enough and applied for a sufficient time. The microorganisms are unable to survive under such environmental conditions. This principal is used for canning of the meat in which properly selected container holding meat is hermetically sealed and given heat treatment for a particular time and temperature.
CANNING OF MEAT PRODUCTS
Preservation of foods by heat processing in OTS (Open Top Sanitary) cans is one of the safest methods. In this method, the growth of pathogenic organisms is inhibited by application of heat energy and partial vacuum produced to retard biological and chemical degradation.
Sequence of steps involved in canning: Meats are presented in the form of chunks, cubes and mince. The sequence of steps can be listed as below: Meat is cooked in steam jacketed kettles + Cooked out juice is separated and used for preparation of brine, sauce, curry, etc. + Cans sterilized in hot water+ Cans filled with meats + Medium is exhausted (to drive away the air in the product and medium and to ensure desired vacuum) by sending through exhaust box for 30 minutes. The product temperature after exhaust should be around 82°C + Can is sealed (seaming) and then conveyed to autoclave for processing + Processing schedule is determined depending on the type of product and size of the can. Normally the processing pressure is 15 psi (pound per square inch) equivalent to 12 1°C for a duration of 50-60 minutes + Cans are cooled in running water-containing chlorine (8 mg / lit) + Cans are properly labeled with all the details about the date of manufacture, batch number, net weight, ingredients, legal declaration about whether they confirm to GRAS (Generally Regarded As Safe), wholesale price, retail price, etc.
CURING AND SMOKING
Historically, curing of meat developed as an art of preservation using common salt. Salted meat undergoing complex ripening reactions assumed a sensory profile of its own, establishing itself as a product of distinct identity. Eventually, other ingredients like nitrate, nitrite, sugar, phosphates, etc., entered the curing mixture, each with a specific role to play in the curing process. Sodium chloride (salt) exerts inhibitory effect on bacterial growth by bringing down the water activity (aw). Nitrite plays an important role in retarding the growth of several bacteria, particularly Clostridium botulinum. The phenolic constituents in smoke also have bactericidal action.
Methods of curing the meats include following two approaches:
a) Dry curing: In this method, salt mixture is applied on the surface of meat and kept in chill room (2-4°C) for 7-10 days.
b) Pickle curing: In this method of curing, the meat is immersed in pickle solution (salt mixture dissolved in water). Pickle solution is prepared by dissolving salt mixture at 60-65° salinometer and the solution is then used for 5-7 days followed by the application of dry salt mix on the surface of meat. The meat is kept at 2-4°C for 5-7 days.
Salts and chemicals used in curing are as follows:
i) Salt (sodium chloride): It is the most important ingredient used in curing of meats – the finished product containing about 2.5 per cent. Microorganisms differ in their power to thrive in the presence of sodium chloride. The halophilic (salt-loving) bacteria like Staphylococcus spp. Grow well in high salt concentration unlike the non-halophilic bacteria, which exhibit slow growth under these conditions. Common salt is an effective inhibitor of microorganisms, imparts flavour and in some cured meats, such as emulsion type products. Serves an important functional role by solubilizing the myofibrillar proteins. The purity of salt is very important. Contamination of salt with metal ions promotes oxidative rancidity.
ii) Nitrate: Sodium nitrate is a vital ingredient for meat curing. It reacts with myoglobin to produce characteristic pink colour in cured meat.
Nitrite affords specific protection against outgrowth of spores of Clostridium botulinum. The finished product should not contain more than 200 ppm of nitrite. A potential problem that may emerge relates to the possibility of nitrite reacting with secondary amines to form nitrosamines, which are carcinogenic.
Smoke: Smoking is an integral part of curing process of meat. It provides specific colour (brownish or mahogany) and preservative and antioxidant effects. Special room is planned out where coal smoke is produced by burning wood or sawdust (oak, hickory, maple, jumper wood). Smoke has mainly formaldehyde whose action is bactericidal and bacteriostatic. However, it causes coagulation of protein and dehydration of the meat.
ANTIBIOTICS AND BACTERIOCINS
Certain substances produced by one type of living organisms such as antibiotics by fungi, and bacteriocins by bacteria, have the property to kill (bactericidal) or inhibit (bacteriostatic) the growth of other organisms. Antibiotics and bacteriocins have potential for preservation of meat as some of them are non-toxic and can be used safely. In case of poultry, certain antibiotics such as tetracycline Meat Preservation and chloromycetin in ice water are used at the time of evisceration for two hours at 3°C.
FERMENTATION
Fermentation is a process in which chemical changes in an organic substrate are brought about through the action of enzymes liberated by microorganisms. During fermentation, microorganisms liberate lactic acid, volatile acids (such as acetic acid), antibiotics and bacteriocins that inhibit the growth of undesirable microorganisms and bring preservative effect in foods. Microorganisms responsible for fermentation are lactic acid bacteria (LAB), certain molds and yeasts. LAB are one of the major groups of microorganisms responsible for fermentation of meat and meat products and for making silage of offals from fish, poultry and animals. The unique character of LAB is the production of lactic acid during fermentation.
PACKAGING
The purpose of packaging is to protect the meat products from microbial contamination, light, physical damage or chemical changes. Even if sound preservatives methods are employed in the handling and storage of meat, poor wrapping techniques or the use of the wrong type of packaging material may lead to deteriorative changes in the meat. Package-product compatibility, therefore, assumes a critical role in determining the product shelf life.
1.Vacuum packaging
2.Modified atmosphere packaging
3.Retortable flexible pouches
4.Cryovac packaging
IRRADIATION
Irradiation or the controlled application of energy from ionizing radiations has been well recognized as a cost-effective method of preservation of meat and meat products. Radiation at low energy level does not induce radioactivity in the food constituents. It will not produce any harmful toxic residues in food and can be used to treat prepackaged commodities. Irradiation achieves disinfestation of insects, enzyme inhibition, destruction of spoilage and pathogenic microorganisms and elimination of parasites of hazardous nature. Irradiation destroys the biological processes that are responsible for spoilage. It does not cause changes in freshness and texture of food. Irradiation produces very little chemical changes in food. None of the changes known lo occur have been Found to be harmful.
HURDLE TECHNOLOGY
The ‘hurdle’ concept of food preservation is the modern concept and based on installing the ‘hurdles or blocks’ in the microbial growth pathways through ‘additive or synergistic effect’ of two or more methods of food preservation.
CONCLUSION
The methods that are commonly used to store or preserve meats, significantly reduce or retard the microbial growth, and therefore, play a vital role in ensuring safety of meat, controlling the spoilage and extending the shelf life. In other words, meat preservation aims at enforcing measures that prevent the occurrence of deteriorative changes in meat brought about by microbial, chemical and physical processes.