Oxidation of skeletal muscle myofibrillar proteins in oil-in-water emulsions: interaction with lipids and effect of selected phenolic compounds.

The effect of selected phenolic compounds, namely, gallic acid, cyanidin-3-glucoside, (+)-epicatechin, chlorogenic acid, genistein and rutin (50 and 200 microM), and alpha-tocopherol (50 microM) against the oxidation of oil-in-water emulsions (37 degrees C/10 days) containing 1% myofibrillar proteins (MPs), was investigated. Emulsions containing 1% bovine serum albumin (BSA) were also prepared for comparative purposes. Protein oxidation was assessed by measuring the loss of natural tryptophan fluorescence and the protein carbonyl gain by using fluorescence spectroscopy. Lipid oxidation was concurrently analyzed by measuring the increase of conjugated dienes (CDs) and hexanal. Proteins inhibited lipid oxidation in oil-in-water emulsions, and MPs showed a more intense antioxidant activity than BSA. MPs were also more resistant to oxidative deterioration than BSA. The different antioxidant capacity of MPs and BSA and their susceptibility to suffer oxidative reactions might be derived from their different amino acid composition and three-dimensional structures. The addition of the phenolic compounds resulted in a variety of effects, including both antioxidant and pro-oxidant effects. Gallic acid, cyanidin-3-glucoside, and genistein were the most efficient inhibitors of lipid and protein oxidation. The chemical structure of the phenolic compounds as well as the nature and conformation of the proteins were greatly influential on the overall effect against oxidative reactions.