Temperature-dependent alcohol acyltransferase reactions as the main enzymatic way to produce short-chain (C4-C8) and medium-chain (C9-C13) esters over the whole Daqu-making process.

Abstract

The ester-synthesis enzymes influenced by environmental factors during Daqu-making process largely determine the flavor of Chinese liquor, but the main ester-synthesis enzyme and its key influencer remain unclear. Here, the volatile ester profiles over the whole Daqu-making process, under different treatments, for at least 90 days, were carefully analyzed, and the potential ester-synthesis enzymes, as well as their dependently environmental factors, were explored. In the detected 46 volatile esters, only the short-chain (C4-C8) and medium-chain (C9-C13) ester content obviously changed, as the primary contributor discriminating different samples. Their trends were both consistent with that of the alcohols and the primary metabolism, which included alcohol acyltransferases (AATs) reaction with alcohols and acyl-CoAs as the substrates. Among the potential ester-synthesis enzymes, the typical AAT activity also exhibited the highest correlation with the short- and medium-chain esters (r > 0.78, P < 0.05). The Mantel test between environmental factors and ester production showed that temperature of Daqu was directly correlated with the short-chain esters (r= 0.58, P < 0.01) and AAT activity (r=0.56, P < 0.01). Further, the short- and medium-chain ester content in Daqu under the treatment nearer to the reported optimal temperature of 40-50 °C of AATs reaction was overall higher than that of the other treatment Daqu. This study revealed that the temperature-dependent AATs reaction was the main enzymatic method producing the short- and medium-chain esters over the whole Daqu-making process. The results could contribute to the flavor improvement of Baijiu. © 2022 Society of Chemical Industry.