Determination of Total Phenols, Total Flavonoids and Antioxidant Activity of Watermelon Peel and Rind from Several Cultivation Areas in Indonesia

Background: Watermelon (Citrullus lanatus) consists of peel and rind (30-40% of total fruit weight), commonly discarded as waste. Nonetheless, several studies have shown the potential benefit of these watermelon parts. This study aimed to determine the correlation between the watermelon cultivation areas and their chemical composition, especially phenols and flavonoids. Watermelon peel and rind were obtained from Jember (WJ), Sragen (WS), Langkat (WL), Hulu Sungai Tengah (WHST) and Lombok Tengah (WLT). Methods: The total phenols and flavonoids were determined by using the colorimetric method. Furthermore, the antioxidant activity was determined by using DPPH and ABTS methods. Result: The highest total flavonoids, i.e. 41.86±1,65 mgQE/100 g watermelon, was observed in the WHST rind. While WL peel showed the highest total phenols, i.e. 3.97±0.02 mgGAE/g. The correlation analysis for all samples showed no significant relationship between the antioxidant activity and total flavonoids. However, a significant relationship was found between the DPPH-IC50 and total phenols with a correlation value of 0.47 (p less than 0.01) for both watermelon parts peel and rind. In addition, watermelon peel contains higher total flavonoids compared to rind. But, there was no significant difference in the total phenols between the watermelon peel and rind. To conclude, both watermelon peel and rind obtained from five cultivation areas showed antioxidant activities contributed by the phenolic compounds.