The negligible role of ellagic acid in preventing fat oxidation of Tunisian walnuts (Juglans regia L.)

Antioxidant activity of phenolic extract isolated from Tunisian walnut (Juglans regia L.) fruits has been investigated. Preliminarily, composition of walnut kernels was determined. Fat content varied from 53.5 to 66.9% (w/w), while total phenol ranged from 1.2 to 5.2 g/100 g of kernel as gallic acid equivalent (GAE). High amounts of ellagic acid (EA) and its derivatives were evidenced by HPLC analysis of the phenolic extract. Walnut fat showed induction time ranging from 2.5 to 3.7 h at 110 °C (rancimat test) and these values unchanged by adding 300 mg/kg of kernel phenolic extract which so showed to have no antioxidant effect. In addition, activities of the ellagic and gallic acids and trolox were compared in vitro by using the Folin–Ciocalteu’s, rancimat and DPPH radical scavenging methods. EA exhibited an antioxidant and radical scavenging activity significantly lower than other tested substances. In conclusion, EA showed to have a negligible role in preventing walnut fat oxidation.