Activity of grape polyphenols as inhibitors of the oxidation of fish lipids and frozen fish muscle

Grape phenolic compounds were obtained from grape (Vitis vinifera) pomace by pressing and posterior maceration. Phenolics resulting of the crude grape extract were fractionated by preparative chromatography. The ability of fractions, containing flavanol monomers, oligomers (procyanidins) and glycosylated flavonols, for inhibiting oxidation of fish lipids was determined. The tests were conducted in fish oils, fish oil-in-water emulsions and in fatty fish species such as mackerel during frozen storage. Partitioning coefficients of grape phenolics showed high solubility in the aqueous media and low in oily media. The results suggest that an optimal combination of procyanidin, degree of polymerization and percentage galloylation may be related to the highest antioxidant efficacy of grape polyphenols in the different systems tested. Monomers were more effective in oily systems. Flavanol oligomers were the most potent inhibitors of oxidation in emulsions and in frozen fish muscle.