Effects of Far-Infrared Radiation Drying on Starch Digestibility and the Content of Bioactive Compounds in Differently Pigmented Rice Varieties.

Far infrared radiation (FIR) was applied to six rice varieties with different coloring of the pericarp (purple, red or non-pigment). Changes were determined in amylose content, in gelatinization parameters, in the content of bioactive compounds, in antioxidant activity and in the in vitro digestibility of pigmented rice as affected by FIR. The highest contents of amylose, total phenolic (TPC), total flavonoid (TFC) and total anthocyanins (TAC) were found in the purple and red varieties. Overall, FIR increased TPC, TFC and TAC, including antioxidant capacity. Quercetin and apigenin contents were increased while rutin and myricetin decreased significantly (p < 0.05) in all FIR-dried samples. Dephinidin, cyanidin-3-glucosides and pelargonidin increased after FIR treatment. Mostly, FIR-treated samples were found to have greater gelatinization enthalpy, compared with unheated rice samples. FIR-dried rice showed lower starch digestibility (25−40%) than unheated rice. This research suggested that the specific genotype of rice had the greatest influence on amylose content in pigmented rice, while FIR drying had no further effect. Our results suggest that FIR could enhance the content of the bioactive compounds capable of inhibiting α-amylase, thereby lowering starch digestibility. Hence, FIR may be considered as an appropriate drying method for pigmented rice regarding health benefits.

Effects of different treatments on the antioxidant properties and phenolic compounds of rice bran and rice husk.

We investigated the changes of antioxidant activity and bioactive compounds in bran, rice husk and ground rice husk after three different treatments, namely hot-air, far-infrared radiation (FIR), and cellulase, compared with raw samples. Overall, FIR-treated group showed a higher DPPH radical scavenging activities, ferric reducing antioxidant power (FRAP), and total phenolic content (TPC) than did hot-air and cellulase treatments for all samples. A significant increase in α- and γ-tocopherols was found in FIR irradiated rice bran compared to raw bran, while α- and γ-tocopherols in hot-air and cellulase treated rice bran were remained unchanged. Cellulase significantly increased the amount of vanillic acid; however a dramatic decrease of ferulic acid was observed. The contents of γ-oryzanol in cellulase treated ground rice husk were significantly increased. Decreasing particle size in the husk was found to work positively for enhancing antioxidant activities, γ-oryzanol and phenolic compounds.