Black rice (Oryza sativa L.) processing: Evaluation of physicochemical properties, in vitro starch digestibility, and phenolic functions linked to type 2 diabetes

Abstract

Black rice is recognized for managing diabetes in Chinese folk medicine. Therefore, the present study investigates the effect of thermal treatments and the succeeding cooking on black rice physicochemical properties, phenolic composition, total antioxidant activity (TAA), enzymes and glycation inhibition in addition to starch digestibility. Thermal decomposition of anthocyanin and cyanidin-3-glucoside was evident across all processing methods and reflected in increasing levels of protocatechuic acid, while proanthocyanidins (TPAC) were susceptible to cooking. Roasting of grains sustained total phenolics (TPC), flavonoids (TFC), TPAC, and antilipase activity. Additionally, the combined effect of frying and cooking diminished TFC, TPAC, and α-glucosidase inhibition. The thermally treated grains showed pronounced activity against α-amylase, α-glucosidase, and glycation, whereas their cooked counterparts reduced the estimated glycemic index (eGI), and enhanced resistant starch (RS). Processed grains chrominance, TAA, and apparent amylose content (AAC) showed a significant correlation with phenolics. These findings are demonstrating that black rice processing is favorable for the dietary management of metabolic disorders such as diabetes and hyperlipidemia.

Keywords: Amylose contents; Black rice; Cooking; Enzyme inhibition; Frying; Phenolic compounds; Roasting; Starch digestion.