Effect of extensive feeding on α-tocopherol concentration and oxidative stability of muscle microsomes from Iberian pigs

The effect of extensive feeding, confinement and diet supplementation with a-tocopheryl acetate (100 mg/kg) on the fatty acid composition and tocopherol concentration of microsome extracts and their susceptibility to oxidation was studied in Iberian pigs. The diet of pigs raised extensively was mostly composed of acorn and grass. The a-tocopherol contents of acorn and grass were 20 and 171 mg/kg dry matter, respectively. Microsomal fatty acid composition showed no differences among groups. Pigs feeding extensively had a higher concentration of a-tocopherol in muscle and microsomes than pigs given mixed diet with the basal level of a-tocopheryl acetate ( P < 0·05) but lower values than pigs given supplementary levels (100 mg/kg) ( P < 0·05). Microsomal fractions from pigs given mixed diet with a basal level of a-tocopheryl acetate were significantly more susceptible to iron-induced lipid oxidation than extract from pigs given diets containing a supplementary level ( P < 0·05). Microsomal extracts from pigs feeding extensively had the lowest oxidation rate ( P < 0·05), suggesting that other dietary constituents may play a role in the stabilization of microsomal lipids.