Isolation, screening, and metabolic characterization of Kroppenstedtia eburnea from the fermented grains of Jiang-flavor Baijiu

Abstract:

[Objective] High-temperature stacking fermentation is a key process in the production of Jiang-flavor Baijiu. Kroppenstedtia is a predominant bacterial genus in the stacked fermented grains, and investigating its growth and metabolic characteristics contributes to comprehensively understanding the crucial role of stacking fermentation. [Methods] The tryptic soy broth was used to screen Kroppenstedtia strains from the stacked fermented grains, and the taxonomic status of each strain was determined by morphological observation and 16S rRNA gene sequencing. Furthermore, the growth characteristics and volatile compound metabolism of each strain were investigated by solid-state fermentation experiments on sorghum at different temperatures (45 ℃ and 50 ℃) in combination with pure culture. [Results] Three strains of Kroppenstedtia were isolated from the fermented grains of Jiang-flavor Baijiu and identified as K. eburnea. The liquid culture of strain K. eburnea 1613 significantly enhanced the production of pyrazines, which was 2.66 folds of that in the control group. The volatile compounds of sorghum in solid-state fermentation predominantly consisted of alcohols and acids, the total content of which increased over the fermentation time. The fermentation at 50 ℃ promoted the accumulation of alcohols, acids, and pyrazines, and that at 45 ℃ facilitated the accumulation of esters. The primary metabolites produced by the three strains during solid-state fermentation with sorghum as the substrate were phenethyl alcohol and isovaleric acid. The fermentation with K. eburnea 1615 at 50 ℃ for 15 days produced the highest levels of phenethyl alcohol and isovaleric acid, which reached (31.17±0.14) µg/g and (16.75±0.76) µg/g, respectively. The fermentation with K. eburnea 6E22 and K. eburnea 1613 at 50 ℃ yielded the highest levels of 2,5-dimethyl pyrazine [(1.67±0.14) µg/g] and hexanoic acid [(3.74±0.19) µg/g], respectively, after 15 days. The accumulation of aldehydes and ketones was significant in sorghum fermented at 50 ℃. The partial least squares-discriminant analysis (PLS-DA) revealed significant influences of temperature and time on the volatile compound composition of sorghum fermented by the three strains. [Conclusion] K. eburnea contributes to the production of flavor compounds in fermented grains, particularly the characteristic flavor compounds such as alcohols, acids, and pyrazines of Jiang-flavor Baijiu.