Anti-microbial and Anti-oxidant Activity of Watermelon (Citrullus lanatus) Fruit and Watermelon Seed

Abstract

Watermelon (Citrullus lanatus) flesh and seeds were dried and pulverized, and their extracts were diffused to sterile discs for the evaluation of anti-microbial activity. The disc-diffusion technique was used to assess anti-bacterial activity against Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Pasteurella multocida, Yersinia enterocolitica, Serratia marcescens, Klebsiella pneumoniae, Xanthomonas campestris, Staphylococcus aureus. Anti-fungal activity against the yeasts Candida albicans and Rhodotorula glutinis was also examined. Standard anti-biotics were also tested as controls. Watermelon flesh and seed extracts were found to be effective against gram-positive and gram-negative bacteria and yeasts. The extracts were also screened for anti-oxidant activity using the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free-radical-scavenging assay, total reducing ability using the Fe3+–Fe2+ transformation method and ferrous ion (Fe2+)-chelating activity. Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), ethylenediaminetetraacetic acid and α-tocopherol were used as reference anti-oxidant radical scavenger compounds. The most potent anti-bacterial activity was demonstrated by watermelon–ethanol extract (inhibition zone 30 mm) against K. pneumoniae, and the most potent anti-fungal activity was demonstrated by watermelon–acetone extract (inhibition zone 26 mm) against R. glutinis. Watermelon–ethanol and watermelon seed–ethanol extracts both demonstrated marked anti-oxidant activity. These results highlight that watermelon fruit and seed extracts have potential for the development of efficient, safe and cost-effective natural anti-oxidant compounds for application in the functional food industries.