Aroma-enhancing role of Pichia manshurica isolated from Daqu in the brewing of Shanxi Aged Vinegar

Daqu is an essential starter for the brewing of Shanxi Aged Vinegar, and high contents of total acid and total ester are two important indices for highly qualified vinegar. The present study is amied to investigate the aroma-enhancing role of a yeast strain screened from Daqu in fortified vinegar fermentation. A Daqu-originated yeast strain Y14 showed the highest ester-producing ability, up to 36.055 g/L, and was identified as Pichia manshurica by sequence analysis of the D1/D2 domain of the 26S rRNA gene in combination with morphological and physiological properties. When it was re-inoculated into the Daqu-based fermentation, Gas Chromatography Mass Spectrometry (GC/MC) analysis for alcohol fermentation showed a significant increase of total alcohol and total ester. The levels of ethanol, ethyl acetate, and isoamyl acetate increased from 31.912%, 9.839%, and 1.025% to 39.861%, 22.707%, and 1.291%, respectively. Moreover, an additional seven volatile aroma components appeared in the Y14 fortified fermentation (FF). Correspondingly in the resulting vinegar, the total acid and total ester markedly increased from 37.4 and 15.3 g/L to 38.0 and 21.5 g/L, respectively. Sensory assay revealed no abnormal odour but a distinct fruity, flowery fragrance and a lingering ester taste in the vinegar of the FF. With this approach, Pichia manshurica isolated from Daqu, when reintroduced into the Daqu-based fermentation, can significantly increase the acid and the ester production, improve the vinegar quality by endowing it flowery and fruity notes, and a long-lingering buttery and nut-like taste.