In Vitro Antioxidant and Antibacterial Evaluation of Optimized Dragon Fruit and Kiwi Fruit Herbal Syrup

Background: Fruit peels are sources of phytoconstituents including polyphenols and flavonoids. Dragon fruit and kiwi fruit peel extracts were incorporated into an optimized herbal syrup to utilize their biological potential. Objective: The study evaluated the in vitro antioxidant and antibacterial activities of an optimized syrup containing ethanolic and aqueous peel extracts of dragon fruit and kiwi fruit. Methods: The optimized syrup contained a total peel-extract load of 5.0% w/v. Antioxidant activity was evaluated using the DPPH radical-scavenging assay at syrup concentrations of 10-50 mg/mL, with ascorbic acid at 20-100 µg/mL as standard. Antibacterial activity was evaluated by agar well diffusion against Staphylococcus aureus and Escherichia coli using ciprofloxacin (5 µg/mL) as positive standard. Results: DPPH scavenging increased from 22.56% at 10 mg/mL to 85.51% at 50 mg/mL. The calculated IC50 values were 25.18 mg/mL for the syrup and 37.92 µg/mL for ascorbic acid. The syrup produced zones of inhibition of 22.4 ± 0.5 mm against S. aureus and 18.6 ± 0.8 mm against E. coli. Net zones were 16.4 and 12.6 mm, and relative antibacterial efficacies were 73.87% and 61.46%, respectively. Conclusion: The optimized formulation demonstrated concentration-dependent DPPH radical-scavenging activity and antibacterial activity against both test organisms, with greater antibacterial activity against S. aureus.