Screening, identification and fermentation conditions optimization of high-yield butyric acid bacteria in pit mud

Butyric acid is an important component of the pit mud aroma in strong-flavor (Nongxiangxing) Baijiu. It could also produce esterification reactions to form ethyl butyrate with alcohol, thereby improving the flavor and taste of strong-flavor Baijiu. Therefore, the content of butyric acid largely affects the style and quality of strong-flavor Baijiu. In order to strengthen regulation butyric acid production through strain and make the Baijiu flavor more controllable, the high-yield butyric acid strain was screened from the pit mud by traditional microbial isolation technology, identified by morphological observation and molecular biology technique, and the fermentation conditions were optimized by single-factor and response surface experiments. The results showed that a strain JN-14 with high butyric acid production was screened from the pit mud. The butyric acid yield was (6.11±0.12) g/L. It was identified as Caproicibacterium sp. The optimal fermentation conditions for butyric acid produce by the strain were as follows: initial pH 8, ethanol addition 2%, and strain JN-14 inoculum 9% (V/V). Under these optimal conditions, the butyric acid yield reached the highest of (8.91±0.25) g/L after fermentation for 7 d. This high-yield butyric acid strain could be applied to the flavor-enhancing fermentation of Baijiu, which was helpful for the regulation and improvement of Baijiu quality.