Manipulating the Fatty Acid Composition of Meat to Improve Nutritional Value and Meat Quality

Abstract This chapter reviews research on the fatty acids in meat, which have major roles in its nutritional value and product quality. Nutritional value is affected by the balance between saturated (SFA) and polyunsaturated (PUFA) fatty acids. Meat is frequently criticized by nutritionists and national health authorities for supplying too much SFA to the diet. On the other hand, meat can be a significant source of long-chain n-3 fatty acids, the intakes of which are widely judged to be too low at present. It would benefit the healthiness and also the image of meat if it supplied less saturated fat to the diet and more PUFA, particularly n-3 PUFA. The use of feeding treatments to change meat fatty acid composition has been a popular research topic in recent years. Use of α-linolenic acid (ALA) in linseed/flaxseed and grass can lead to deposition of ALA in tissues and synthesis of the metabolically-important long-chain n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, synthesis is low, particularly of DHA; and EPA and DHA together do not usually reach the levels required for the meat to be labelled as a “source” of n-3 fatty acids. Higher levels can be achieved in all species when sources of EPA and DHA are fed, in fish oil or algae. In all species, the bulk of PUFA are deposited in phospholipid (PL) in muscle and limits to high concentrations of PUFA are the small amount of PL and the animal’s need to retain functioning membranes with a balanced fatty acid composition. Feeding treatments often achieve peak concentrations of PUFA quickly because sites for deposition are swamped. A particular problem in beef and sheep is that the rumen breaks down PUFA to SFA and MUFA so the balance between PUFA and SFA absorbed from the gut is much lower than in pork and chicken. Nevertheless, the use of grass feeding can achieve useful levels of EPA and DHA, particularly in sheep. In pork and chicken, the deposition of long-chain PUFA in adipose tissue, as well as muscle means that products, such as sausages, which contain both tissues, can more easily reach “source” concentrations. High levels of PUFA in meat can lead to lipid oxidation postmortem which may negatively affect the flavor of cooked meat and the color of displayed meat. Beef and sheep muscle are particularly susceptible to lipid oxidation. The antioxidant vitamin E is the key to controlling oxidation and good quality products, with levels of n-3 PUFA exceeding “source” values, can be produced if muscle concentrations of vitamin E are maintained at 3–4 mg/kg. This is achieved by feeding grass, which contains vitamin E naturally, or by supplementing diets with “supranutritional” levels of vitamin E (200–500 mg/kg). Even with antioxidant protection, however, lipid oxidation can be triggered when post mortem procedures promote oxidation. These include extended ageing, high oxygen packaging, extended display under light, and cooking. Research in this area will continue to search for more effective feeding strategies which optimize fatty acid composition and the oxidative stability of meat. Possible new approaches are considered in the review.