Effects of extraction solvents on phenolic contents, in vitro antioxidant, and antimicrobial activities of roselle (Hibiscus sabdariffa L.) Calyx
Belay Haile Kebede, Reath Lul Them, Betelhem Abera Mengistu
Abstract
• The study explores solvent effects on bioactive compounds in Roselle calyx. • Phytochemicals, antioxidants, and antimicrobial properties of calyx were analyzed. • Methanol is identified as the most effective solvent for extracting Roselle calyx. • Study enhances Roselle extraction for better use in food, medicine, and supplements. Hibiscus sabdariffa L., commonly known as Roselle, is a valued plant of the Malvaceae family, cultivated in tropical and subtropical regions. Roselle is consumed as a vegetable in hot and cold preparations and is associated with numerous health benefits. Despite its widespread use, research on bioactive compounds remains limited, particularly in Ethiopia. This study investigated effects of extraction solvents on phytochemical content, antioxidant and antimicrobial activity of Roselle calyx. The 80 % methanolic extract showed highest total phenolic content, while n-hexane extracts (60 % and 80 %) had lowest. Total flavonoid content peaked in 80 % chloroform extract, with n-hexane showing lowest levels. In antioxidant assays, 80 % methanol demonstrated strongest activity (lowest IC 50 in DPPH assay), while 60 % n-hexane was weakest. Antibacterial tests revealed 80 % methanol and cold water extracts were effective against Escherichia coli and S. aureus (25 mm inhibition zones) whereas n-hexane showed no antibacterial activity. Greatest fungal biomass reduction occurred with 80 % n-hexane, while 60 % methanol showed least reduction. A strong negative correlation ( r = −0.882; p < 0.05) between IC 50 of DPPH and total phenolic content highlighted antioxidant-phenolic relationship. Further research on Roselle's health-promoting qualities could advance natural medicine and nutrition, offering opportunities for functional foods and therapeutic applications.