Comparative antioxidant and antimicrobial activities of the peels, rind, pulp and seeds of watermelon (Citrullus lanatus) fruit

Abstract

This study investigated the antioxidant and antimicrobial effects of the peel, rind, pulp and seeds of C. lanatus (watermelon) as well as their respective phytochemical composition. The antioxidant effect was investigated using the DPPH and ABTS assay whereas the antimicrobial activity was evaluated using the well diffusion and broth dilution methods. The results revealed that the peel possessed the highest antioxidant activity whereas the pulp demonstrated the lowest. The peels demonstrated the highest antimicrobial effect, which was followed by the seed and then the rind. The pulp, however, demonstrated the least antimicrobial activity. A strong correlation was observed between total phenolic contents and biological activity. The peels were found to possess the highest content of total phenolics (0.087±0.002 mgGAE/g), which was followed by the seed (0.042±0.003 mgGAE/g) and the rind (0.026±0.003 mgGAE/g). The pulp did not only demonstrate the lowest antioxidant and antimicrobial activities but also had the lowest phenolic content (0.010±0.001 mgGAE/g). The peel and the seed show the presence of flavonoids whereas alkaloids and free reducing sugars were present in all parts of the watermelon fruit. From the results of the current study, it can, therefore, be concluded that among the various parts of the watermelon fruit, the peel has the highest antioxidant and antimicrobial activity whereas the pulp has the least. The peels and seeds are not only potent in their antioxidant and antimicrobial effects but also possess appreciable levels of phenolic compounds relative to the other parts.

Keywords

• Antimicrobial
• Antioxidants
• Metabolites
• Phenolics
• Watermelon