Vinegar production from post-distillation slurry deriving from rice shochu production with the addition of caproic acid-producing bacteria consortium and lactic acid bacterium

To establish a zero emission process, the post-distillation slurry of a new type of rice shochu (NTRS) was used for the production of health promoting vinegar. Since the NTRS post-distillation slurry contained caproic acid and lactic acid, the effect of these two organic acids on acetic acid fermentation was first evaluated. Based on these results, Acetobacter aceti CICC 21684 was selected as a suitable strain for subsequent production of vinegar. At the laboratory scale, acetic acid fermentation of the NTRS post-distillation slurry in batch mode resulted in an acetic acid concentration of 41.9 g/L, with an initial ethanol concentration of 40 g/L, and the acetic acid concentration was improved to 44.5 g/L in fed-batch mode. Compared to the NTRS post-distillation slurry, the vinegar product had higher concentrations of free amino acids and inhibition of angiotensin I converting enzyme activity. By controlling the volumetric oxygen transfer coefficient to be similar to that of the laboratory scale production, 45 g/L of acetic acid was obtained at the pilot scale, using a 75-L fermentor with a working volume of 40 L, indicating that vinegar production can be successfully scaled up.