Comprehensive analysis of antioxidant and antibacterial activities of water and methanol extracts of Hibiscus flower

Abstract

This study provides a comprehensive investigation into the antioxidant and antibacterial properties of Hibiscus flower extracts, highlighting their potential for future applications in functional foods. The research addressed key challenges by employing a multi-faceted approach, including four distinct methods for evaluating antioxidant potential: DPPH and FRAP assays, reducing power, and chelating ability of Fe ions. Total phenolic content was quantified using the Folin–Ciocalteu method, while tannins and flavonoids were assessed via vanillin–HCl and aluminum chloride assays. Additional analyses included spectrophotometric measurement of total flavonols and anthocyanins. Antibacterial activity was determined using a modified agar disk diffusion method, with results indicating significant inhibition of Salmonella typhimurium and Staphylococcus aureus by both aqueous and methanolic extracts. Colorimetric analysis revealed a reduction in chroma and hue angles, while FTIR spectroscopy identified key functional groups, such as suberin, lipids, and polysaccharides. Notably, the antioxidant efficacy varied depending on the solvent used, with aqueous extracts showing higher total phenolic content (4325.12 mg GAE/100 g) compared to methanolic extracts (3487.05 mg GAE/100 g). The study concludes that Hibiscus flower extracts, rich in antioxidants like tannins and anthocyanins, possess significant potential for use as natural preservatives and colorants in food products, supporting their role in developing novel functional foods.