The extension of vacuum microwave drying time improved the physicochemical properties, in vitro digestibility and antioxidant activity of brown rice flour

In this study, the effects of vacuum microwave drying (VMD) time on the physicochemical properties, digestibility and antioxidant activity of brown rice flour (BRF) were investigated. BRF samples were treated with VMD at 6 W/g, 70 °C and 0.08 MPa vacuum pressure for 2, 4, 6, 8, and 10 min, respectively. Compared with the control group, VMD increased water solubility index (+29.68%, at 8 min) and amylose content (+16.73%, at 10 min). The thermal analysis results showed that the crystallinity of starch from brown rice reduced and became more homogeneous after microwave treatment. The in vitro digestion results indicated that VMD treatment decreased the digestibility of BRF samples. The content of resistant starch increased from 24.53% to 27.21%–31.55%. In addition, the soluble phenolics content of BRF samples subjected to VMD treatment ranged from 108.99 to 114.43 mg GAE/100 g dry weight (DW), higher than that of the control group (103.95 mg GAE/100g DW), thus significantly improving free radical scavenging activity. In conclusion, VMD can be used as a drying and modification method for better quality BRF production in the future.