Effects of roasting conditions on bioactive compound profile of purple maize (Zea mays L.) using response surface methodology

Abstract

The objective of this study was to optimize the roasting temperature and time for caffeine-free beverage production from purple maize kernels. Response surface methodology (RSM) was used to optimize the temperature and time. Purple maize kernels were roasted at different temperatures (100, 120, 140, 160 and 180 ° C) and different times (10, 15, 20, 25 and 30 min.), subsequently extracted with ethanol. The condition used for extraction process was purple maize/ethanol ratio (1:10) which was controlled in the water bath for 4 hours at 32 ° C. Total phenolic content, total anthocyanin content, antioxidant activity values EC₅₀ determined by 2,2–diphenyl–1–picrylhydrazyl (DPPH) and free sugar were analyzed. The levels of total phenolic content, anthocyanin content, DPPH radical scavenging activity and free sugar were 138.30-908.30 mg gallic acid equivalent/g crude extract, 3.27-258.57 mg of cyanidin-3-glucoside equivalent/100g dry seed, 10.80-847.83 g flour/g DPPH and 0.02-1.06 g/100ml, respectively. Considering the results of the total phenolic content and anthocyanin content, it was found that they increase gradually when temperature rising from 100-180 ° C and reached highest at 160 ° C. Meanwhile antioxidant activity values EC₅₀ and free sugar content were found lowest at 160 ° C. According to bioactive compound analysis, antioxidant efficiency was increased at the higher levels of total phenolic content and anthocyanin content. Therefore, the roasting temperature was the important factor effecting the bioactive compounds. The contour plots indicated that the optimum roasting temperature and time were 160 ° C and 25 min. respectively.