Optimization of Process Parameters for the Extraction of Anthocyanins from Black Rice Bran Using Response Surface Methodology

This study aimed to optimize different process parameters for the extraction of anthocyanins from black rice bran using Response Surface Methodology (RSM). To determine its degradation profile, the stability of crude anthocyanin extract (CAE) against selected biologically relevant buffers was also evaluated. Two-level full factorial and Box-Behnken designs were employed in the screening and optimization of extraction parameters, respectively. CAE was prepared from black rice bran using conventional and optimized methods, and the resulting extract was determined for their phytochemical content and antioxidant scavenging activities. Stability of the optimized CAE was further evaluated using biologically relevant buffers for 48 h. Results showed that the optimum conditions for the extraction of anthocyanins were 60% ethanol, 0.2% hydrochloric acid, and 215 min of extraction. The CAE obtained from the optimized method was 4 times higher in anthocyanins, 2.3 times higher in 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 1.7 times higher in phenolics and ferric reducing antioxidant power (FRAP) values, and 1.5 times higher in flavonoids than that obtained from the conventional method. In terms of its stability, the optimized CAE did not undergo substantial degradation at pH 1, while significant degradation was observed at pH 7.4. Addition of 10% newborn calf serum had no significant effect on the stability of anthocyanin. The half-life of anthocyanins from the optimized CAE ranged from 29.0 to 32.5 h based on first order kinetics. The study suggests that RSM is a practical and effective statistical tool that can be used to optimize the best conditions in extracting anthocyanins from black rice bran.