Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 20 : Preparation and Processing of Meat

Post mortem changes

The changes taking place in meat after slaughter may be grouped under two heads

1. Onset of rigor mortis and
2. Development of tenderness in muscle

• Onset of rigor mortis: The first biochemical change occurring in muscle is rapid glycolysis of the glycogen represented by the presence of enhanced lactic acid content in muscle. The lactic acid content of muscle after rigor mortis is as high as 0.9 per cent. The muscle becomes stiff due to rigor mortis. Rigor mortis was correlated with the disappearance of ATP. In the absence of ATP, actin and myosin combine to form rigid chains of actinomyosin. Just before an animal is slaughtered, the muscles are soft and pliable. But immediately upon death, stiffening of the carcass known as rigor mortis occurs. It is 24-48 hours in beef.


• Conditioning or tenderization of meat: When meat is stored at < 00C, biochemical changes take place in meat leading to the development of tenderness in meat. This process is called conditioning of meat. The tenderness is due to


• Denaturation of the meat proteins and
• Mild hydrolysis of denaturated meat proteins by the enzyme cathepsin present in meat

The increase in tenderness is followed by an increase in water soluble amino nitrogen indicating mild proteolysis of the muscle proteins. Contrary to the general belief, there is practically no change in the connective tissues and collagen. There is no increase in water soluble hydroxyl proline peptides indicating collagen has not been acted upon by proteolytic enzymes.

• Artificial tenderization of meat: Cold storage facilities are required for the natural tenderization of meat. Artificial tederization of meat has been developed by using proteolytic enzymes such as papain (from papaya), bromelin ( from pineapple) or trypsin (from pancreas). The enzyme is usually injected into the animal, half an hour before slaughtering. The meat obtained from such animal becomes tender within 24 hours.
  
  These post-mortem effects bring about changes in the quality attributes of meat, such as
• Texture
• Water-holding capacity
• Colour and
• Flavour
  Nutritional quality is not that much affected.


• Aging:
• If meat is held cold for sometime for 1 or 2 days after it has completed rigor mortis, the muscles again becomes soft and pliable with improved flavour and juiciness which is called resolution of rigor. Some changes that take place during this period are known as ageing or ripening.
• During ageing there is progressive tenderisation of meat owing to the denaturation of the muscle proteins by the intracellular proteolytic enzymes, the cathepsins.
• Ageing or ripening is done by holding meat at 0.50 to 200C temperature in a cold room. Aging may take 1-4 weeks. The best flavour and the greatest tenderness develop in meat aged from 2 to 4 weeks.
• During ageing, humidity of the cold room is to be controlled and meat may also be affected by holding it at a higher temperature for a shorter time usually 200 C for 48 hours.
• Ageing with even higher temperature for lesser time is practised commercially. In such cases, ultraviolet light is used to keep down surface bacterial growth.
• Beef is usually the only kind of meat that is commercially aged. Lamb and mutton are occasionally aged. Pork is never aged because of its high fat content.


• Tenderising
  
  Tenderness is the most desired characteristics in meat. The amount and distribution of connective tissues and the size of both muscle fibres and bundles of fibre determine the tenderness of meat. The number and strength of cross linkages between the peptide chains of collagen increase with the age of the animal and this decreases the amount of collagen that may be solubilised during cooking thus contributing to decreased tenderness. There are different methods of tenderising meat. Exercise increases tenderness of meat.


• Cold-room storage results in the ripening of meat with tenderising from the natural enzymes of meat.
• The mechanical methods of tenderising meats include pounding, cutting, grinding, needling or pinning and the use of ultrasonic vibrations. Mechanical methods cut or break the muscle fibres and connective tissues.
• The art of using enzymes for tenderising meat is an old one.


• Wrapping of meat in papaya leaves before cooking results in tenderisation. This is the result of the action of the enzyme papain on meat proteins.
• Other enzymes used for meat tenderisation are
  
  • Bromelain from pineapple
  • Ficin from figs
  • Trypsin from pancreas and fungal enzymes.
    These proteolytic enzymes
    
    
    • Catalyze the hydrolysis of one or more meat proteins.
    • The enzymes also hydrolyze the elastin of the connective tissues.
    • To achieve uniform tenderness, papain is injected into the veins of
    • animals some 10 minutes before their slaughter.
      
• Tenderising enzymes remain active until the meat is heated. Papain is inactive at 55oC.
• Meat may be tenderised by the use of low levels of salts.
  
  
  • Salts increase the water-holding capacity of muscle fibres resulting in tenderness and juiciness.
  • Salt also solubilises the meat proteins.
  • Tenderness of meat is improved when freezer dried meat is rehydrated in a weak salt solution instead of water.
  • Salts used for tenderising are
    
    • Sodium chloride
    • Sodium bicarbonate and
    • Sodium and potassium phosphate.
      
• Another method of increasing tenderness in meat is by change of pH.
• Decreasing or increasing the pH of meat increases hydration and to its tenderness.
• Soaking beef for 48hrs in concentrated vinegar increases its tenderness and juiciness.
• Exercised animals give tender meat.


• Curing of Meat
• Curing of meat brings about the modification in meat that effects preservation, unique flavour, red colour and tenderness due to added curing agents.
• The ingredients used for curing of meat are
• Common salt
• Salt retards microbial growth and gives flavour to meat
• Sodium nitrate or nitrite
• Nitrite fixes the red colour of myoglobin, develops flavour and inhibits clostridium botulinum
• Sugar
• Sugar helps stabilize colour, counteract saltiness and also add flavour
• Spices
• Spices are added mainly for flavour
• During the curing process, the curing mixtures may be rubbed dry on the surface of cut meat or the meat may be immersed in a solution of the curing agent (pickling).
• The curing ingredients may be much more rapidly and uniformly distributed throughout the meat by pumping the solutions via an artery if it is intact or the cure may be injected with multiple needles into the cut of meat.
• As per Codex Alimentarius, the nitrate in meat products can be 150-500 mg/kg.


• Cuts and Grades
• Carcass quality usually refers to composition and conformation.
• The gross composition of the carcass considers the proportion of muscle, fat and bone. These are influenced by age, weight, breed and other similar factors. As the animal increases in age
• The ratio of lean mass and of fat to bone increases
• The amount of fat increases and
• The amount of total moisture decreases in the soft tissues.


• Conformation refers to the proportionate development parts of the carcass and to the ratio of meat to bone.
• Meat carcasses are commonly divided into relatively larger wholesale cuts and these are further divided into smaller retail cuts.
• Distinguishing features of a cut of meat are
• The size, shape and location of bone
• The size and shape of muscle found in the cut and
• the amount and distribution of fat.
• The commonly used meat in India is lamb mutton. About 70.0% of all meat used comes from sheep and goat. The wholesale cuts of lamb are legs, loin, racks, breasts and shoulders. Each of the wholesale cut is further cut into retail cuts such as chops, roasts and neck slices. Meat sold in the market must be wholesome and fit for human consumption.
• Meats are also graded for quality. Two major factors used to evaluate the quality or palatability of meat are maturity and marbling. The maturity of animal affects the texture, firmness and colour of the meat.
• Marbling, which refers to the amount and distribution of fat appearing as white flecks within the lean, is an important index of quality. The quality, consistency and character of juices or extractives contained in muscle fibres also contribute to the quality of meat.
• Good quality lamb mutton has a smooth covering of clean white brittle fat over most of the exterior. The lean meat is pinkish red in colour in lamb and deeper red in mutton. The texture of the lean is fine grained and velvety in appearance. The bones are porous and reddish in colour in lamb and they are hard and white in mutton. Poor quality meats have darker flesh and the grain is coarse and fibrous. The fat layers are heavy and have a strong flavour.




Table: summarises the desirable characteristics to be observed while buying meat.

Table: Desirable characteristics in meat

Type	Meat	Fat	Bone
Bacon (back/sides of a hog)	Bright red	Small flecks of white fat, firm, brittle, loamy, white, odourless
Veal(calf)	Pale pink, firm, not soft and flabby. Cut Surface moist	No fat	Pinkish white, porous with a small quantity of blood in their structure
Lamb	Pinkish red	Fine grained and velvety appearance	Porous and reddish
Mutton	Deep red	No yellow, no strong flavour	Hard and white
Pork	Lean	Should be white, firm, not excessive	Small and fine pinkish