Optimization of fermentation conditions for production of ethyl caproate in Baijiu using a selected isolate of Saccharomyces cerevisiae

Saccharomyces cerevisiae is indispensable in the production of Baijiu. This yeast not only produces ethanol, but also produces many flavorsubstances that impart unique quality characteristics to Baijiu. Ethyl caproate (EC) is the main flavor substance of strong-flavor Baijiu(SFB). S. cerevisiae that can produce a high yield of EC is critical for SFB production. In the present study, S. cerevisiae isolate YF1914produced an EC content of 1.27 mg/L, which was greater than that produced by other test isolates obtained from several Baijiu brewingenvironments. Through single factor experiments, the influence of various factors on EC production by YF1914 was measured. Eightvariables were tested using a Plackett-Burman design, and ethanol content, induction time, caproic acid content, initial pH, and temperaturesignificantly affected EC production. Further studies were done using the steepest ascent path and response surface methodology (RSM)designs to identify optimized fermentation conditions for EC production. The optimum conditions were found to be: sorghum hydrolysatemedium (SHM) with a sugar content of 12 Brix and an initial pH of 5.0, inoculum size 5% (v/v), incubation at 28 °C with shaking at180 rpm for 32 h, addition of 10% (v/v) ethanol and 0.046% (v/v) caproic acid at 32 h, then static culture at 24 °C for 32 h. Theoptimized conditions produced an EC content of 21.98 mg/L or 17.3 times greater than the content obtained using initial conditions. Thus,a selected S. cerevisiae isolate with high EC yield was obtained, which can potentially improve SFB quality by increasing EC content.Keywords: ethyl caproate; optimization; Saccharomyces cerevisiae; strong-flavor Baijiu