Phytochemical and Antibacterial properties of the seed of watermelon (Citrullus lanatus)

Watermelon seed was evaluated for its phytochemical and antimicrobial potentials. Crude extract of the seeds was obtained using hot water, cold water, ethanol and methanol. Test organisms were screened to confirm their viability and identities using standard microbiological methods. Extracts were tested for antimicrobial activity using the standard disc diffusion assay method against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae and Bacillus cereus. All the seed extracts showed evidence of antibacterial properties. Hot water extract showed the highest antimicrobial activity against Pseudomonas aeruginosa with 14mm diameter zone of inhibition whereas ethanol and methanol extracts showed the lowest against Escherichia coli and Klebsiella pneumoniae with 8mm diameter zone of inhibition. Watermelon seed showed low antimicrobial activity when compared to the result of the commercial antibiotics. The analysis for phytochemical constituents was performed using generally accepted laboratory techniques for quantitative determinations. The constituents analyzed for were tannins, saponins, flavonoids, cyanogenic glycosides, oxalates and alkaloids. Alkaloid had the highest concentration of about 1.23% whereas cyanogenic glycoside had the lowest of about 0.00237%. There was a correlation between the phytochemical levels and the antimicrobial activities. The low level of phytochemicals explains the low antimicrobial activities of extracts of watermelon seeds