Lipid and colour stability of beef from grazing heifers supplemented with sunflower oil alone or with fish oil.

The effect of sunflower and fish oil supplementation of grazing heifers on lipid oxidation and colour stability in beef was investigated. For 150 days, heifers were assigned unsupplemented grazing (G) or restricted grazing with 2.5kg concentrates containing 1250I.U. α-tocopheryl acetate and 290g sunflower oil (S1), 415g sunflower oil (S2), 290g sunflower+85g fish oil (FS1) or 415g sunflower+85g fish oil (FS2). Longissimus dorsi muscle was excised 24h post-mortem and stored at -30°C prior to analysis. Muscle α-tocopherol in the oil-supplemented groups was higher (P<0.05) than the G group. Lipid oxidation in refrigerated, minced raw or cooked beef was not significantly affected by diet but metmyoglobin was higher (P<0.05) in raw beef from oil-supplemented groups compared to the G group. Lipid oxidation and metmyoglobin formation increased (P<0.001) during refrigerated storage. Vitamin E supplementation together with pasture grazing appeared to offset any potential deleterious effect of oil supplementation on lipid and colour stability.