Effect of Ethanol Stress on the Fatty Acid Ethyl Ester Biosynthesis Pathways of Baijiu Brewing Yeast

The flavor and scent of Chinese Baijiu are closely linked to the quantity of fatty acid ethyl esters, and their generation is closely associated with Baijiu brewing yeast, most notably ethyl acetate (EA) and ethyl hexanoate (EH). At present, however, the specific mechanism of EA and EH produced by Wickerhamomyces anomalus under ethanol stress during the brewing of Baijiu remains unclear. Our study findings revealed that ethanol stress inhibited the generation of precursor substances (pyruvate and acetyl-CoA) in the fatty acid ethyl ester biosynthesis pathway of W. anomalus NCU003. The high level of EA produced in the fatty acid ethyl ester biosynthesis pathway was associated with the enhanced expressions of ATF1 and EAT1 and the increased activity of C2 esterase under 3% and 6% ethanol stress. The lower EA content was related to the high expression of IAH1 and low activity of C2 esterase under 9% ethanol stress. We also found that the expression of ACC, FAS1, FAS2, EHT1, and EEB1 was up-regulated, which may promote the synthesis of EH under ethanol stress, whereas the activity of C6 esterase may have no effect on the synthesis of EH. Our study results indicated that the above genes and C2 esterase can be modulated in W. anomalus NCU003 under ethanol stress, thus promoting the synthesis of fatty acid ethyl esters during the brewing of Baijiu.