Optimization of extraction parameters for phenolic compounds from black rice bran

Abstract:

Black rice bran is one of the richest plant-based sources of anthocyanins and phenolic acids, yet its commercial exploitation has been held back by inconsistent extraction yields. This research optimized extraction conditions for total phenolic compounds (TPC) from Thai black rice bran (cultivar Riceberry) using response surface methodology with a central composite design. Three independent variables—extraction temperature (40-80 °C), time (30-90 min), and solvent-to-solid ratio (1:10-1:30 v/w, 70% ethanol)—were investigated across 20 experimental runs. TPC ranged from 11.8 to 42.7 mg gallic acid equivalents (GAE) per gram of bran. The second-order polynomial model was significant (p<0.001) with an R² of 0.964 and a lack-of-fit p-value of 0.218. Temperature and time were the most influential variables, contributing 38.4 and 27.1 percent to TPC variation, respectively. The predicted optimum—68 °C, 54 min, and a 1:22 solvent ratio—yielded 43.1 ± 1.6 mg GAE/g in verification runs, within 2.3 percent of the model prediction. At the optimum, total flavonoid content was 18.9 mg quercetin equivalents/g, DPPH radical scavenging reached 87.3 percent, and ABTS activity was 91.6 percent. These results provide a validated extraction protocol for recovering phenolic antioxidants from black rice bran at pilot-plant scale.