Antioxidant Dietary Fiber from the Bran of Five Philippine Pigmented Rice Varieties

Pigmented rice varieties are considered rich sources of antioxidant dietary fiber (ADF); consuming them may have health benefits. In this study, bran samples of five Philippine pigmented rice varieties namely, Red-64, Black Rice, Calatrava, Arabon, and Dinorado were analyzed for their ADF contents. The bulk of dietary fiber in the bran of the five varieties is insoluble dietary fiber (IDF), while a very minimal amount is soluble dietary fiber. Calatrava (CL) exhibited the highest total dietary fiber (52.5%), consisting primarily of 50 percent IDF. The CL IDF exhibited the highest total phenolic content (1.8 mg gallic acid equivalents [GAE]/gram dry weight [DW]) and total anthocyanin content (0.524 mg cyanidin-3-glucoside /100 g DW). The CL IDF also displayed the highest antioxidant activity in terms of ferric ion-reducing antioxidant power (17.72 μmol trolox equivalents/gram DW), ABTS*+ radical scavenging activity (33%), and DPPH radical quenching activity (76.7%, 3.9 mg ascorbic acid per gram DW). The majority of the phenolics associated with CL IDF is in the bound form amounting to 6.9 mg GAE/g DW. High-performance liquid chromatography revealed the presence of gallic acid, resorcinol, vanillin, ferulic acid, salicylic acid, and quercetin in the bound phenolic extract. As this study has established that the CL IDF is an ADF believed to possess many health-promoting properties, it can be valorized for potential applications in nutraceuticals and functional foods.