THE EFFECTS OF DIETARY ALPHA-TOCOPHEROL AND OXIDIZED LIPID ON POSTTHAW DRIP FROM CATFISH MUSCLE

DL-alpha-tocopheryl acetate was added at different concentrations (20 or 100 mg kg(-1)) to catfish diets containing either fresh or oxidised (rancid) oil to determine the effects on tissue alpha-tocopherol leve ls, fatty acid composition and post-thaw exudative moisture loss from fillets of African catfish (Clarias gariepinus). Following a 56-day fe eding trial in which duplicate groups of twenty 15.7-g catfish were fe d diets at a ration level of 3% body weight per day, it was recorded t hat for any given oil status, muscle alpha-tocopherol responded signif icantly (P < 0.05) to elevations in dietary DL-alpha-tocopheryl acetat e. Oil quality exerted a profound effect on muscle alpha-tocopherol le vels, with fillets from fish fed oxidised diets exhibiting significant ly (P < 0.05) lower alpha-tocopherol concentrations, despite similar d ietary tocopherol-ester contents. Decreased PUFA content was recorded in fillets from fish fed rancid-oil diets, although dietary alpha-toco pherol was successful in lessening the effect. Post-thaw exudative moi sture losses from fillets after refrigerated storage for 48 h was sign ificantly (P < 0.05) greater in treatments fed oxidised- rather than f resh-oil diets. Within the oxidised treatments, elevated dietary alpha -tocopheryl acetate inclusion resulted in a lessening of the moisture loss, thus demonstrating the protective effect of vitamin E against fr eeze damage of muscle-tissue membranes. After 96 h, the significant di fferences (P < 0.05) in exudative losses between treatments was solely due to muscle alpha-tocopherol concentration. Hence, alpha-tocopherol was shown to be the most important factor in the maintenance of post mortem membrane stability. In this investigation supplemental dietary vitamin E afforded some degree of protection to Clarias tissues, again st the stresses involved with the consumption of rancid feeds. (C) 199 7 Elsevier Science B.V.