Technological and acid stress performance of yeast isolates from industrial sourdough

Abstract

Yeast populations in sourdough have been poorly characterized from baking-relevant attributes as leavening activity in a stressful environment. In particular, the presence of extracellular acids represents an important challenge, which compromises the growth and fermentative metabolism of microbial starters. Here, we have analyzed the fungal diversity of six industrial sourdoughs identifying Saccharomyces cerevisiae and Kazachstania humilis as the predominant species. The volatile organic compounds (VOC) profile revealed differences between sourdough samples which can be attributed, at least in part, to their microbial composition and ingredients used in each one. In particular, K. humilis appeared to contribute to the presence octan-1-ol, 2-hepten-1-ol, 2-octen-1-ol, nonan-1-ol and 2-pentylfuran in the sourdough. A total of 45 yeast isolates were then analyzed in terms of CO2 production and tolerance to NaCl, ethanol, oxidative-, cold- and heat-stress, which allowed the selection of 5 S. cerevisiae isolates and 2 from both K. humilis and Torulaspora delbrueckii for further characterization. Overall, K. humilis isolates showed a higher total CO2 production and gassing rate than a commercial yeast strain used as a control. Hence, the isolated strains are potential candidates for the development of new sourdough starters and the basis for a further selection of variants with superior performance.