Manipulating meat quality and composition

Meat quality describes the attractiveness of meat to consumers. The present paper focuses on two major aspects of meat quality, tenderness and flavour . Both aspects of quality can be influenced by nutrition, principally throu gh its effects on the amount and type of fat in meat. In several countries, high levels of intramuscular fat (marbling fat), i.e. above 30g/kg muscle weight in longissimus, are deemed necessary for optimum tenderness, althoug h poor relationships between fat content and tenderness have generally been found in European studies, where fat levels are often very low, e.g. below 10g/kg in UK pigs. Muscle lipid may be a marker for red oxidative (type 1) muscle fibres which are found at higher concentrations in tender muscles a nd carcasses. Nutritional treatment can be used to manipulate the fatty aci d content of muscle to improve nutritional balance, i.e. increase the polyu nsaturated (PUFA):saturated fatty acid value and reduce the n-6 : n-3 PUFA value. Increasing PUFA levels may also change flavour because of their grea ter susceptibility to oxidative breakdown and the generation of abnormal vo latile compounds during cooking. This situation particularly applies to the n-3 PUFA which are the most unsaturated meat lipids. In pigs, a concentrat ion of 3 mg alpha-linolenic acid (18:3)/100 mg in muscle and fat tissue fat ty acids can easily be achieved by including whole linseed in the diet. Thi s level has led to abnormal odours and flavours in some studies, but not in others. In cattle and sheep, feeding whole linseed raised 18:3 concentrati ons in muscle fatty acids from about 0.7mg/100mg to > 1 mg/100 mg. As with pigs, this diet also increased levels of long-chain n-3 PUFA formed from 18 :3, including eicosapentaenoic acid (20:5). Although this increase led to g reater oxidative breakdown of lipids during storage and the generation of l arge quantities of lipid-derived volatile compounds during cooking, there w ere no deleterious effects on odour or flavour. When 18:3 levels are raised in lamb and beef because of grass feeding, the intensity of the flavours i ncreases in comparison with grain-fed animals which consume and deposit rel atively more linoleic acid (18:2). In ruminants, very high levels of 18:2 p roduced by feeding protected oil supplements cause the cooked beef to be de scribed as oily, bland or pork-like.