| Abstract
| - Natural phenolic antioxidants have been tested in hake (Merluccious merluccious) microsomes asinhibitors of lipid oxidation promoted by fish muscle prooxidants: hemoglobin (Hb), enzymatic NADH-iron and nonenzymatic ascorbate-iron. The phenolics selected were as follows: (a) a grape phenolicextract (OW), (b) a fraction (IV) with isolated grape procyanidins with a medium-low degree ofpolymerization and galloylation percentage, (c) hydroxytyrosol obtained from olive oil byproducts,and (d) a synthetic phenolic antioxidant, propyl gallate. All compounds delayed lipid oxidation activatedby Hb, enzymatic NADH-iron, and nonenzymatic ascorbate-iron, excluding hydroxytyrosol that wasnot an effective antioxidant on oxidation promoted by nonenzymatic iron. The relative antioxidantefficiency was independent of the prooxidant system, IV> propyl gallate > OW> hydroxytyrosol,and showed a positive correlation with their incorporation into microsomes (p< 0.05). The reducingcapacity or ability for donating electrons and the chelating properties may also contribute to theantioxidant activity of phenolics, although these factors were less decisive than their affinity forincorporating into the microsomes. Conversely, the inhibition of Hb oxidation by phenolics and theirpolarity did not seem to play an important role on antioxidant mechanism. These results stressed theimportance of incorporating the exogenous antioxidants into the membranes where are located keysubstances for fish lipid oxidation (highly unsaturated phospholipids, iron-reducing enzymes, andendogenous α-tocopherol). Keywords: Fish; hemoglobin; enzymatic iron; nonenzymatic iron; lipid oxidation; microsomes; grapepolyphenols; hydroxytyrosol
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