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

The flavor and scent of ChineseBaijiuare closely linked to the quantity of fatty acid ethyl esters, and their generation is closely associated withBaijiubrewing yeast, most notably ethyl acetate (EA) and ethyl hexanoate (EH). At present, however, the specific mechanism of EA and EH produced byWickerhamomyces anomalusunder ethanol stress during the brewing ofBaijiuremains 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 ofW. anomalusNCU003. The high level of EA produced in the fatty acid ethyl ester biosynthesis pathway was associated with the enhanced expressions ofATF1andEAT1and the increased activity of C2 esterase under 3% and 6% ethanol stress. The lower EA content was related to the high expression ofIAH1and low activity of C2 esterase under 9% ethanol stress. We also found that the expression ofACC,FAS1,FAS2,EHT1, andEEB1was 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 inW. anomalusNCU003 under ethanol stress, thus promoting the synthesis of fatty acid ethyl esters during the brewing ofBaijiu.