Studies on the antioxidant and antibacterial activity of Costus igneus leaf powder- a natural preservative for food

Abstract

Food products are rich in nutrients but are highly susceptible to microbial spoilage and oxidative degradation, necessitating the use of preservatives. Due to safety concerns associated with synthetic additives, natural plant-based bioactive compounds are gaining prominence. Costus igneus, traditionally used for diabetes management in Tamil Nadu, is reported to possess significant antioxidant and antimicrobial properties, making it a promising natural preservative source. The present study evaluated the phenolic content, antioxidant potential and antibacterial activity of ethanolic extracts of C. igneus leaf powder for potential application in food systems. The total phenolic content, determined using the Folin-Ciocalteu method, was found to be 96.43±1.50 mg GAE/g, indicating a high concentration of polyphenolic antioxidants. The extract exhibited concentration-dependent DPPH radical scavenging activity, with inhibition values increasing from 37.89±0.14 % at 25 µg/ml to 88.20±0.23 % at 400 µg/ml and an IC₅₀ value of 31.06 µg/ml. Although the activity was lower than that of standard ascorbic acid, the extract demonstrated strong free radical scavenging potential. Antibacterial analysis showed that the extract inhibited Staphylococcus aureus, Bacillus cereus, Escherichia coli and Pseudomonas aeruginosa, with the highest activity observed at 500 µg/ml. Gram-negative bacteria, particularly P. aeruginosa and E. coli, were more susceptible to the extract. Overall, the study demonstrates that C. igneus leaf powder possesses notable antioxidant and antibacterial properties, supporting its potential use as a natural preservative in functional foods and nutraceutical application.