Antioxidant Activity of Watermelon Seeds Determined by DPPH Assay

The purpose of this study was to assess the antioxidant activity of the fresh extracts of Croatian and Greek watermelon seeds. Samples were prepared using two extraction methods: Soxhlet and maceration. Ethanol was used as a solvent in the Soxhlet, and methanol in the maceration method. The mass fractions of the extracts obtained by maceration were lower compared to those obtained by the Soxhlet method. The antioxidant capacity of fresh watermelon-seed extracts was determined by DPPH (2,2-diphenyl-1-picrylhydrazyl radical) method. The antioxidant capacity of the extracts was also expressed via IC 50 (half maximal inhibitory concentration). Based on the obtained IC 50 values (1.41 to 2.60 mg ml −1 ), all tested extracts showed antiradical activity but antioxidant capacity was better in extracts obtained by the maceration method. The reason for this may be the use of methanol as a solvent, which was to be expected, since methanol is a more polar solvent than ethanol. The neutralisation capacity of DPPH radicals of analysed extracts was compared to the neutralisation capacity of ascorbic acid as standard. The concentrations of tested extracts required to neutralize 50 % of DPPH radicals were significantly higher than the required concentration of ascorbic acid (0.25 mg ml −1 ).