48 pigs (gilts and barrows) were divided into four groups and fed for three months on diets containing either 3 % soya oil or 3 % beef tallow, together with a-dl-tocopheryl acetate at either a basal (20 mg/ kg feed) or a supplemented (200 mg/kg feed) level. The fatty acid compositions of the longissirnus dorsi muscle (m.1.d.) and adipose (backfat) tissue were found to vary with dietary fats and sex. Gilts showed higher contents of polyene fatty acids (PFA) than barrows. The PFAs C20:4w6, C22:4w6, C22:503 and C22:6w3 were not affected by the diet. Levels of a-tocopherol in muscle and adipose tissue were 2.5 to 4.0 times higher in pigs on the supplemented diet compared to pigs on the basal diet. After storage at -18°C for nine months the muscle tissues were subjected to iron-induced lipid peroxidation. Supplementation of the feed with a-tocopheryl acetate improved the oxidative stability of the muscle. The influences of dietary fat and sex on lipid peroxidation were reduced by supplemental a-tocopheryl acetate. Muscle tissue from the basal-diet/soya-oil group was more susceptible to lipid oxidation than muscle tissue from the basal-diet/beef-tallow group.
I n t r o d u c t i o n
During the storage and preparation of meat, many primary and secondary oxidation products such as aldehydes, dialdehydes, ketones, esters, furans, alcohols, hydrocarbons and lactones are formed'. These volatile compounds, together with break-down products of the amino acids, affect flavour and aroma2. T h e occurrence of warmed-over flavour in cooked meat products, caused by the oxidation of phospholipids3, is a well-documented example of the importance of controlling lipid oxidation in meat. Feeding pigs with vitamin E at high levels increases the a-tocopherol content of the membranes4. The formation of thiobarbituric-acid-reactive substances (TBARS) during storage' and the induced oxidation of fresh neat^.^ is delayed by feeding vitamin E a t higher levels.
Stability against oxidation is influenced not only by the levels of antioxidants but also by the fatty acid composition of the meat'. This is also a determining factor for the flavour of pork'. A s early as 1926, Ellis and Isbell'o*'' demonstrated that the fatty acid composition of pork fat was dependent o n the types of fat consumed with the feed. There was a particularly good correlation in the case of linoleic acid.