Effect of Solvents on the Antioxidant Activity of Walnut (Juglans regia L.) Shell Extracts

Walnut shell is a waste generated in the walnut (Juglans regia L.) harvest, containing natural compounds with antioxidant properties. In this connection, the effect of the solvent (water, chloroform, methanol, ethanol, ethyl acetate and N-butanol) on the extraction yields, total flavonoids content and antioxidant properties was analyzed. Total flavonoids content of extracts was determined by NaNO2-Al(NO3)3 method. Extract antioxidant activity was measured by hydroxyl, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide anion radical scavenging capacity and the total antioxidant capacity and reducing power assay. The highest extraction yield was achieved with N-butanol (4.54%) and the greatest total flavonoids content shown by the samples extracted with ethyl acetate. The highest ability to scavenging DPPH, hydroxyl and superoxide radicals was ethyl acetate extract (EC50=81.03μg/mL), methanol extract (EC50=131.35 μg/mL) and chloroform extract (EC50=176.35μg/mL) respectively under the concentration of 500 μg/mL. The methanol extract showed the greatest total antioxidant activity and reducing power. The results showed that different solvent had significant effect on total flavonoids content and antioxidant activity. The result obtained demonstrated the potential of walnut shell as a source of antioxidant.