The effect of supplementation of pig diets with grape seed extract (GSE) (100, 300, 700mg/kg feed) and bearberry (BB) (100, 300, 700mg/kg feed) for 56 days pre-slaughter, on the oxidative stability and quality of raw and cooked M. longissimus dorsi (LD) was examined. Susceptibility of porcine liver, kidney and heart tissue homogenates to iron-induced (1mM FeSO(4)) lipid oxidation was also investigated. In raw LD steaks, stored in modified atmosphere packs (75% O(2):25% CO(2)) (MAP) for up to 16 days at 4°C, surface lightness (CIE 'L' value), redness (CIE 'a' value), lipid stability (TBARS, mg MDA (malondialdehyde)/kg muscle) and pH were not significantly affected by supplemental GSE or BB. Similarly, the oxidative stability and sensory properties of cooked LD steaks, stored in MAP (70% N(2):30% CO(2)), for up to 28 days at 4°C, were not enhanced by dietary GSE or BB. Iron-induced lipid oxidation increased in liver, kidney and heart tissue homogenates over the 24h storage period and susceptibility to oxidation followed the order: liver>heart>kidney. Dietary GSE or BB did not significantly reduce lipid oxidation in tissue homogenates. Potential reasons for the lack of efficacy of supplemental GSE and BB on pork quality were explored.