Candida Ethanolica Strain Y18 Enhances Aroma of Shanxi Aged-vinegar

Abstract

Daqu is an essential starter for the fermentation of Shanxi aged-vinegar. Despite numerous studies on the microbial diversity in Daqu, there is little information on the use of autochthonous yeasts originated from Daqu for vinegar fermentation. Herein, an ester-producing yeast strain, designated Y18 (33.48 g L⁻¹ ester), was isolated from Daqu. The strain Y18 was identified as Candida ethanolica based on sequence analysis of the D1/D2 domain of the 26S rRNA gene, in combination with the morphological and physiological characteristics. The results of gas chromatography-mass spectrometry showed that inoculation of Y18 into the Daqu-based fermentation broth increased the relative abundances of total alcohols and total esters in the Jiulao compared to the non-inoculated control. In particular, the relative abundances of ethanol, isoamyl acetate, and ethyl acetate increased from 31.9% to 38.0%, 1.0% to 1.5%, and 9.8% to 14.5%, respectively. Five different aroma compounds (isoborneol ethanol, isobutanol, benzoic acid methyl ester, acetic acid 2-phenylethyl ester, and hexanoic acid phenyl ester) were detected in the Y18-fortified alcoholic fermentation broth compared to the non-inoculated control. After Y18 fortification, the levels of total acids and total esters in the vinegar increased from 37.42 and 15.30 g L⁻¹ to 40.24 and 19.25 g L⁻¹, respectively. The sensory analysis of Y18-fermented vinegar revealed no abnormal odors but distinct fruity and flowery aromas, with slightly sweet and lingering taste. In conclusion, the inoculation of C. ethanolica strain Y18 into the Daqu-based fermentation broth could markedly enhance the aroma of the Shanxi aged-vinegar by increasing the contents of total acids and total esters, and improve the vinegar quality by conferring the flowery and fruity flavors and slightly sweet, nut-like taste.