Extraction of walnut leaves extracts with microwave assisted extraction and evaluation of antioxidant properties of phenolic compounds

Recently, there is an increasing trend to use natural antioxidants due to undesirable effects of synthetic antioxidants. In this study, phenolic compounds of shahmirzadi variety of walnut leaf were extracted with traditional and microwave assisted extraction (MAE) methods. In traditional method, extraction was performed with methanol 80%, ethanol 50% , boiling water and water at ambient temperature (6, 12, 18 and 24 hours) and in MAE it was done with methanol 80%, ethanol 50% (2, 4. 6 and 8 minutes) and boiling water (3, 6 and 9 minutes). Total phenolic content was determined by Folin-Ciocaltue reagent. In MAE, methanol extract of walnut leaf had the highest total phenolics with 130.16±0.19 mg/g. The antioxidant capacity of extracts was assessed through reducing power assay, DPPH radical-scavenging activity and total antioxidant activity. Extracts showed antioxidant activity in a concentration-dependent way. The ethanol extract of leaves in the reducing power assay and DPPH radical-scavenging activity and the methanol extract of leaves in the antioxidant activity assay presented the highest antioxidant activity. Finally, the influence of methanol extract in retarding the soy bean oxidation was examined. Our results showed that extracts could prevent formation of initial and secondary products of oxidation and an extract with 1000 ppm phenolic content could control oxidation of oil. Hence we can present shahmirzadi walnut leaves as a potential source of natural antioxidants.