Process Optimization for Fermentative Production of Black Rice Vinegar

Black rice (Oryza sativa) also known as forbidden rice, restricted only in northeast Asia, is now being cultivated in some Indian states and has a huge potential for producing vinegar being rich in health-promoting characteristics. In the current study, enzymatic saccharification of black rice carried out using commercial amylases was optimized by response surface methodology (RSM) at 45 degrees C with 5.5 pH. The optimized saccharified starch showed a Brix of 13.5 degrees B with 10.937 g/100 mL and 8.602 g/100 mL of total sugars and reducing sugars, respectively. The saccharification validation of 2L showed a maximum of 14 degrees B, 13.1 g/100 mL total sugars and 10.89 g/100 mL reducing sugars. The ethanolic fermentation of hydrolyzed starch was carried out using Saccharomyces cerevisiae KY069279, which led to 6.532% (v/v) ethanol at a fermentation efficiency of 93.11% and 0.47 g/g of ethanol productivity. The acetic acid fermentation was carried out post-ethanol production using indigenous acetic acid bacteria, Acetobacter aceti AC1. The fermented vinegar showed 4.15% (w/v) volatile acidity at 64.7% fermentation efficiency and 0.38 g/g acetic acid productivity. The produced rice vinegar was found to be rich in antioxidants with a 77.8% DPPH scavenging activity at 50.93 mu M concentration. The vinegar was found to be of standard quality with a mean sensory score of 7.92 +/- 0.8 by a panel of 10 semitrained judges.