Selection and application of potential whole-cell enzymes in the esterification of Huangshui, a by-product formed during Chinese liquor-making.

Huangshui is a by-product of Chinese liquor and it has a high annual production owing to the popularity of the liquor in China. The aim of this study was to investigate the feasibility of Huangshui esterification by whole-cell enzymes produced from different microbial strains. Esterification of Huangshui was carried out for 16 days via the addition of different preparations produced from Rhizopus chinensis strain 3.1149, Rhizopus chinensis strain 3.1166, Monascus purpureus SICC 3.19 and Rhizopus oryzae SICC 3.623. The results showed that the preparation GP1, produced from M. purpureus, exhibited the highest esterification efficiency compared with the other preparations based on physicochemical analysis in combination with volatile profile analysis. In addition, a characterization of preparation GP1 was performed and the optimal alcohol content and pH for esterification were 10% and pH 3.5, respectively. Under the optimal conditions, the total ester content increased from 4.86 to 7.31 g/L after esterification for 16 days. An estimation of the sensory impact of the volatile compounds after esterification was performed by a calculation of the odour active values (OAVs). Radar diagrams of the OAVs demonstrated the differences in the sensory profiles in Huangshui, before and after esterification. Nearly all of the OAVs of the esters were increased by the esterification reaction and were above the human sensory threshold. Results presented in this manuscript provide a potential strategy for the efficient bio-conversion of Huangshui. Copyright © 2014 The Institute of Brewing & Distilling [ABSTRACT FROM AUTHOR]