Abstract
The objective of this research was to investigate the effect of dry heating temperature and time on radical scavenging activities and bioactive compounds in black rice (Oryza sativa L. (indica)) kernels. The experimental design as response surface methodology (RSM) was used to determine the optimum temperature and time. Black rice kernels 25 samples were dry heated at different temperatures (80, 100, 120, 140 and 160 degree celsius) and different time (10, 15, 20, 25 and 30 minutes) and subsequently extracted with 95% ethanol respectively. The antioxidant activity values EC50 determined by 2-diphenyl-1-picrylhydrazyl (DPPH) assays at low temperature were 165.89 g flour/g DPPH and EC50 decreased when increasing temperature. Also the total monomeric anthocyanins content from 165.20 mg/L was decreased to 1.23 mg/L, but high total phenolics contents increased when increasing temperature from 72.09 to 150.59 GAE mg/g crude extract. Free sugar content was analysed by HPLC and decreased from 4052.05 to 15.47g/100 ml when increasing temperature. The results showed overall values of the black rice varieties were significantly affected by the dry heating temperature and that was important factor affected to the quality of the black rice varieties. The contour plots indicated that the optimum dry heating temperature and time were 120 degree celsius and 25 minutes respectively.
