Ultrasound assisted extraction of polyphenolic compounds from red sorghum (Sorghum bicolor L.) bran and their biological activities and polyphenolic compositions

Ultrasonic-assisted extraction (UAE), using aqueous ethanol as the solvent, was firstly applied to extract polyphenolic compounds from red sorghum bran. In this study, ultrasonic time (min), ethanol concentration (%) and solvent to solid ratio (mL/g) were investigated and optimized using a Box-Behnken design. The optimized result for UAE was 21 min of ultrasonic time, 53% of ethanol concentration, and 52:1 mL/g of solvent to solid ratio, 49.743 mg GAE/g dw of yield of total polyphenolic. The experimental results under optimal extraction conditions were in good correlation with the predicted results. Compared to conventional solvent extraction (CSE), UAE obtained a higher yield of total polyphenolic. In addition, UAE extracts showed excellent DPPH radical scavenging activity, reducing power and antiproliferative activity in a dose-dependent manner, and better than that of CSE extracts. Furthermore, the polyphenolic compositions of the extracts were identified using HPLC-ESI-MS/MS. The most abundant polyphenolic compounds in red sorghum bran extracts were taxifolin, taxifolin hexoside, procyanidins, and epicatechin. Taken together, UAE could effectively increase the yield of polyphenolic compounds from red sorghum bran. In addition, these polyphenolic compounds could be used as a potential source of natural antioxidants.