Crop Process Engineering

Lesson 10. Meat and Meat Processing

10.1  Chemical Composition of Meat

 Meat is composed of water, fat, protein, minerals and a small proportion of carbohydrate. The most valuable component from the nutritional and processing point of view is protein. The lean meat contains 20-22 percent proteins. The quality of raw meat and its suitability for further processing is depends on the protein content. The fat content is higher in entire carcasses than in lean carcass cuts. The fat content is also high in processed meat products where high amounts of fatty tissue are used. The fat content of meat varies from 5 – 40 per cent with the type, breed, feed and age of the animal. Carbohydrates are found only in very small quantities in meat.

 10.2 Processing of Meat

 The advantage of meat processing is the integration of certain animal tissues like, muscle trimmings, bone scrap, skin parts or certain internal organs in to the food chain as valuable protein rich ingredients. The basic meat product processing technologies; cutting and mixing are accomplished by various additional treatments like curing, seasoning, smoking, filling in to rigid containers, vacuum packaging, canning. This treatment depends upon the type and quality of the final product. The main objective of processing is to prevent it by inhibiting microbial decomposition. Processing technologies for meat products will not deliver satisfactory results, if there is no adequate meat hygiene in place. All the slaughtering equipments used during processing should be made of stainless steel or plastic and should be rust resistant and easily cleaned & sterilized.

 Curing: The curing of meat brings about the modification of meat that affects preservation, flavor, color and tenderness due to added curing agents. The prime purpose of curing is to produce the unique flavored meat products and a special purpose is to preserve the red color of meat. The ingredients used for curing are common salt, sodium nitrate or nitrite, sugar and spices. Salt retards microbial growth and gives flavor to the meat. Nitrite fixes the red color of myoglobin, also a beneficial effect on the flavor of cured meats and an inhibitory effect on Clostridium botulinum. Salt adds to the taste of the final product. The content of salt in sausages, hams, corned beef and similar products is normally 1.5-3 %. Sugar helps stabilize color, counteract saltiness and also adds flavor. Spices are added mainly for flavor.

 During curing by salts, the high osmotic pressure of the external fluid initially draws water and soluble proteins out of the meat. Later, salt diffuses into the meat and binds to the proteins, causing some expelled protein to diffuse back in. This causes a swelling of the meat. The salt-protein complex that forms binds water well.

 Curing has also some detrimental effects during storage. The pink color of nitrite cured meat changes to brown, in the presence of oxygen. Thus, cured meat should be preferentially packed in containers from which oxygen has been excluded. The salts of cured meat enhance oxidation of lipid components and thus reduce shelf life.

 Smoking: A cured meat may be dried and smoked. Smoking also was originally used as a method of preservation but today smoking is used mostly for its flavor contribution and coagulation of proteins. Ham is frequently processed by smoking. Slow smoking is preferable since the extended period enables more drying to occur on the surface. Drying is responsible for much of the preservative action of smoking. The smoke contains compounds having antiseptic properties which destroy the microorganism present in meat. Smoking also prevent of rancidity in meat.

Cooking of Meat: Cooking of meat is done in order to improve the texture of meat. The method and requirement can make meat tender or less tender than the original raw cut. When meat is cooked, three types of changes contribute to increase tenderness;

i)  the melting of fat,

ii) dissolution of collagen in hot liquids to become soft gelatin and

iii) tissue softening and muscle fiber separation.

 Overheating can cause muscle fibers to contract and meat to shrink and become tougher; evaporation of moisture occurs and dried out tissues become tougher.

 There are two methods of cooking meat; the dry heat and moist heat methods. Selection of the method to use for a meat cut depends upon whether it is a tender or less tender cut. For any method of cooking, an appropriate cooking temperature must be chosen. Generally, lower cooking temperature for a longer period of time is better than a higher temperature for short periods of time for any degree of doneness. This results in decreased drip loss, less shrinkage, increase juiciness and more uniform color throughout the cut.

 a) Dry Heat method: Tender cuts of beef, lamb and pork may be cooked by these methods.

 Roasting: Roasting is one of the simplest and most commonly used methods of cooking meat. The meat is placed uncovered on a rack in a shallow pan to keep the meat out of drippings. The meat is adequately cooked till browning of meat for good flavor and  appearance. For small roasts, an oven temperature of 177⁰C is used. Roasts continue to cook at the centre even after they are removed from the oven. This is because heat is transmitted into the interior from the outer surface.

 Broiling: Broiling is cooking of meat by direct radiant heat, such as the open fire of a gas flame, live coals or electric oven. In open fire or coal broiling heat comes from below, whereas in oven broiling, the heat comes from above. The Broiling is carried out at a temperature of 176 ⁰C until the topside is brown. The Broiling is a faster method of cooking meat by dry heat than roasting. Roasting produces more juicy and tender meats than broiled meats. However, meats with unusual flavor can be obtained by broiling by marinating meats in some types of salad dressings or juices an hour before broiling. This treatment also permits some hydrolysis of protein to occur and thus produces small increases in tenderness.

 Pan broiling:  In pan broiling, heat is transferred to meat primarily by conduction from the pan or griddle. Meat is placed in a cold griddle and heated so that meat cooks slowly. Pan broiling is the preferred method of cooking for thin cuts of meats, because the equipment required for cooking is simpler. A low temperature is sufficient to brown the meat. Pan broiled meat should be turned occasionally to ensure uniform heat penetration.

 Frying:  The cooking of tender cuts of thin (about 1-1.5 cm thick) meat by pan frying or deep fat frying. In pan frying, a small amount of fat/oil is added to the frying pan so that the melted fat is about 0.5 cm deep. In deep fat frying, the melted fat will be deep enough to cover the meat.

 b) Moist heat Methods Moist heat method is used for less tender cuts of meat. This method consists of combination of moisture, heat and a long period of cooking causes meat to become tender owing to the conversion of connective tissue to gelatin. The different moist heat methods are explained below;

 Braising: After broiling the meat, small amount of water is added to the browned meat and the pan used for cooking is covered with a tight fitting lid and cooked with a low heat the meat becomes tender.

 Stewing: Large pieces of tough cuts are cooked in water until tender. The meat is placed in a kettle or vessel with sufficient quantity of water to cover the meat. The vessel is then covered and allows the water to simmers.

 Pressure cooking: In pressure cooking, cooking is done in steam at a temperature higher than that of boiling water. Quality wise pressure cooked meat is less juicy and cooking losses are great.