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 IC50 (half maximal inhibitory concentration). Based on the obtained IC50 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). This work is licensed under a Creative Commons Attribution 4.0 International License.

Svrha ovog istraživanja bila je procijeniti antioksidativno djelovanje ekstrakata svježih sjemenki lubenice uzgojenih u Hrvatskoj i Grčkoj. Ekstrakti su pripremljeni dvjema metodama: Soxhletovom metodom i maceracijom. Etanol je upotrijebljen kao otapalo u Soxhletovoj metodi, a metanol u maceraciji. Maseni udjeli ekstrakta dobiveni maceracijom niži su od onih dobivenih Soxhletovom metodom. Antioksidacijski kapacitet ekstrakta svježih sjemenki lubenice određen je metodom DPPH (2,2-difenil-1-pikrilhidrazilni radikal). Antioksidacijski kapacitet ekstrakata također je izražen s IC50 (polovica maksimalne inhibitorne koncentracije). Na temelju dobivenih vrijednosti IC50 (1,41 do 2,60 mg ml−1), svi ispitani ekstrakti pokazali su antiradikalno djelovanje, ali je antioksidacijski kapacitet bio bolji u ekstraktima dobivenim metodom maceracije. Razlog tome može biti upotreba metanola kao otapala, što se moglo očekivati budući da je metanol polarnije otapalo od etanola. Kapacitet neutraliziranja DPPH radikala analiziranih ekstrakata uspoređen je sa standardom za neutraliziranje askorbinske kiseline. Koncentracije svih ispitnih ekstrakata potrebne za neutraliziranje 50 % radikala DPPH bile su znatno veće od potrebne koncentracije askorbinske kiseline (0,25 mg ml–1). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.