Phytochemical content, antioxidant capacity, and in vitro antibacterial activity of bran extracts of Philippine rice (Oryza sativa) cultivars

Rice bran is a by-product of the milling process that contains compounds with possible therapeutic properties. However, it is underutilized. This study assessed the phytochemical content, namely free, bound, and total phenolic (TPC), flavonoid (TFC), and anthocyanin (TAC) contents; antioxidant capacity using the 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging assay; and in vitro antibacterial activity of crude extracts from the bran of six (one white, two red, three black) selected Philippine rice varieties. Cyanidin-3-glucoside (C3G) and trans-ferulic acid (TFA) were quantified through High-Performance Liquid Chromatography. The in vitro antibacterial activities of extracts (0.1, 0.5, and 0.7 g/mL) against the gram-positive food pathogens Staphylococcus aureus and Clostridium perfringens were evaluated by agar well diffusion assay. Of the five samples, the red rice Kamanga recorded the highest free phenolics (121.01 mg gallic acid equivalents (GAE)/g), TFC (90.14 mg rutin hydrate equivalents/g), and DPPH antioxidant capacity (368.23 µmol Trolox equivalents/g). Generally, black brans had higher TAC, especially Ominio (17.81 mg C3G equivalents/g), which also had the highest bound phenolic content (125.6 mg GAE/g). C3G was only detected on black brans, with at least six-fold more in Ominio than in the other tested varieties. Only the extracts from pigmented varieties, except Ominio, displayed inhibitory potential against the food pathogens, implying that C3G is not the major component imparting the inhibitory activity in the black rice varieties. Therefore, pigmented rice brans can be explored as cheap sources of phytochemicals with antioxidant capacities and natural antibacterial agents for the food and pharmaceutical industries.