Antioxidant activity of a hydrothermal extract from watermelons

- Hydrothermal extraction of watermelon parts was carried out.
- Antioxidant activity of watermelon parts increased with increase in treated temperature and time.
- Several new phenoic compounds were identified in hydrothermal watermelon extracts.

In this study, the antioxidant activity of hydrothermal extracts of different parts of watermelons (flesh, white rind, and green rind) was evaluated. Each part of the watermelons was extracted at temperatures ranging from 100 °C to 300 °C for 10, 30, or 60 min. The highest total phenol content was observed for the green rind extracted at 300 °C for 30 min with 7626.52 μg gallic acid equivalents (GAE)/g, whereas the phenol content of the untreated green rind extract was 715.15 μg GAE/g. The antioxidant activity of the watermelon parts increased with increase in treatment temperature and time. In GC-MS analysis, catechol, 4-methylcatechol, pyrogallol, and 1,2,4-benzenetriol were detected after hydrothermal extraction at 300 °C for 30 min. These results indicate that hydrothermal extraction is an efficient process for increasing the antioxidant activity of watermelon extracts.