Function and safety evaluation of Staphylococcus epidermidis with high esterase activity isolated from strong flavor Daqu

This study was aimed at evaluating the safety of Staphylococcus epidermidis YTPW-4 isolated from strong flavor Daqu and its beneficial functional characteristics in Baijiu-making. The content of ethyl caproate catalyzed by crude enzyme solution of Staphylococcus epidermidis YTPW-140 was 583.09 mg/100 mL, and the activity of esterase was 2.13 U/mL. Vancomycin, erythromycin, and gentam were sensitive to the strain, which was negative for the causative gene, hemolytic activity, and biofilm formation capacity. In addition, the strain was selected for laboratory-scale fermentation using HS-SPME-GCMS and statistical analysis to confirm its role in the production of flavor compounds. Propyl-3-methylbutyrate, hexanoic acid, and ethyl acetate had higher contents after fermentation than other flavor compounds, at 530.40 μg/L, 471.07 μg/L, and 297.33 μg/L, respectively. There was also a small amount of ethyl hexanoate in these products. Esterase could increase the levels of short-chain free fatty acids, which were precursors of flavor compounds. Most importantly, the isolate maintained viability under simulated pit conditions, and was resistant to pH 3.5 and 8% ethanol. These results indicated that the strain had the potential to be used as a starter to improve the quality of Nongxiangxing baijiu.