Phenolic compound profile and biological activities of Southern African Opuntia ficus-indica fruit pulp and peels

Opuntia species have been used in traditional medicine for decades and research on Opuntia plants and their byproduct valorisation are also on the increase. This study investigated the phenolic compound profiles and biological activities of Opuntia prickly pear fruit and peel extracts and the effect of drying methods on extract yields and bioactivities. Ethanolic, methanolic and hexane extracts of freeze-dried Opuntia peels showed better in vitro antioxidant and antimicrobial activities compared to oven-dried peel and fruit pulp extracts. In most cases, freeze-dried samples also showed better extract yields. Antibacterial activities of the extracts were better against Gram-positive (inhibition zone range of 8.0-18.8 mm) compared to Gram-negative (inhibition zone range of 10.0-14.0 mm) bacterial strains. Minimum inhibitory concentrations (MICs) ranged from 2.50 to 18.75 mg/mL. The presence of pinellic acid is reported for the first time in Opuntia fruit extracts. Phenolic acids, flavonols and flavonoid derivatives were also identified. Opuntia peel and fruit pulp extracts were rich in biologically active phenolic compounds and could have potential nutraceutical and food industry applications.