ANTIOXIDANT ACTIVITY OF ENGLISH WALNUT (JUGLANS REGIA L.)

ABSTRACT Phenolic contents of different fractions (contents of whole nut, skin and kernel) of English walnut (Juglans regia L.) were determined and their antioxidative capacities investigated using a number of in vitro model systems. Phenolic compounds extracted from walnut skin into 95% ethanol contained the highest amount of total phenolics and exhibited the highest antioxidative capacity as evaluated by the trolox equivalent antioxidant capacity assay. Extracts of walnut phenolics showed a high ferrous ion chelating ability and effectively scavenged 2,2′-diphenyl-1-picrylhydrazyl radicals, the latter considerably stronger for the skin with 50% inhibition concentration of 3.4 µg extract per mL. Further, inhibition of 2-thiobarbituric acid reactive substances formation in a bulk corn oil model system was also significant (P < 0.05) for all three phenolic extracts and for pure gallic acid at 10 ppm gallic acid equivalents final assay concentration after four days of storage at 60C. PRACTICAL APPLICATIONS Walnut is a healthful nut that contains alpha-linolenic acid in its lipid fraction, and its skin is rich in polyphenolics with strong antioxidant properties, as demonstrated in this study. Thus, walnut with skin and skin of walnuts serve as good free radical scavengers and could be effective in reducing oxidative stress among other beneficial health effects, which could be exploited for product development.