Antioxidant and antimicrobial properties of freeze-dried banana and watermelon peel powders

Abstract

The objective of this study was to determine the antioxidant and antimicrobial properties of banana and watermelon peels. The freeze-dried peels were extracted using aqueous methanol, ethanol, acetone and water. The solvent: water ratios for banana and watermelon peels were 80:20 and 70:30, respectively. The total phenolic contents and DPPH radical scavenging activities of extracts were determined. The antimicrobial activities of the extracts were tested against Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Escherichia coli, Pseudomonas aeruginosa, Salmonella Enteritidis and Salmonella Typhimurium. The total phenolic content extracting efficiencies of solvents were in order methanol > acetone > ethanol for banana peel, while those were acetone > methanol > ethanol > water for watermelon peel. The highest total phenolic content was in the methanolic extract of banana peel (49.21 mg GAE/g DW), while it was in the acetone extract of watermelon peel (13.48 m GAE/g DW). DPPH radical scavenging activities of banana and watermelon peel extracts were 34.78–50% and 30.33–50.89 %, respectively. Bacillus cereus was sensitive to all extracts of both fruit peels. None of the banana peel extracts inhibited Listeria monocytogenes. Salmonella serotypes were resistant to all watermelon peel extracts. The other bacterial strains were sensitive to at least one of the extracts, with inhibition zones ranging from 8 to 23 mm. From the results of the current study, it can be concluded that the freeze-dried banana and watermelon peels have the potential to be sources of bioactive compounds. However, the antioxidant and antimicrobial activity levels strongly depend on the solvent type.