Gamma-aminobutyric acid, total anthocyanin content and antioxidant activity of vinegar brewed from germinated pigmented rice

Abstract

Objective: The aim of this study was to produce healthy fermented vinegar from germinated pigmented rice. Methodology: The experiment was divided into four groups including germinated Hom Nil rice (purple rice), germinated Riceberry rice (purple rice), germinated Hom Mali Daeng rice (red rice) and control rice (ungerminated Riceberry rice). Vinegar was prepared using germinated pigmented rice as the raw material and was supplemented with red yeast rice, alpha-amylase and glucoamylase during saccharification, as well as Saccharomyces cerevisiae E1118 and Acetobacter pasteurianum TISTR 102 during alcohol and acetic acid fermentation. The functional and physicochemical properties of the vinegar were studied. Results: After 4 days of alcoholic fermentation, the alcohol content reached 8.55% for all rice powder samples, whereas the total soluble solids content decreased from 12.04-14.03EBrix to 4EBrix. During the acetic acid fermentation, there was little change in pH, although the acidity increased from 0.51-2.82%. The concentration of gamma-aminobutyric acid (GABA) in all samples ranged between 1.14 and 1.73 mg L-1 and the highest GABA content was found in the germinated Hom Nil rice. The germination process for all pigmented rice samples decreased the total anthocyanin content compared to the control samples. All vinegar samples had antioxidant activity, especially the 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity in vinegar from germinated Riceberry rice and germinated Hom Mali Daeng rice that was relatively high compared to other samples. The sensory test revealed that samples of germinated Hom Mali Daeng rice exhibited a higher overall acceptance score than the other samples. Conclusion: This study indicated that brew-germinated pigmented rice vinegar could be used as a new product with antioxidant activity that was comparable to other vinegar products.