Evaluation of five commercial non-Saccharomyces yeasts in fermentation of soy (tofu) whey into an alcoholic beverage

Soy (tofu) whey is a nutritious liquid substrate that is often discarded by tofu manufacturers. Recent research has shown that tofu whey can be converted into a soy alcoholic beverage using Saccharomyces yeasts. In this study, five commercially available non-Saccharomyces yeasts (Torulaspora delbrueckii; Lachancea thermotolerans; Metschnikowia pulcherrima; Pichia kluyveri and Williopsis saturnus) were evaluated in tofu whey fermentation and each of the yeasts showed different growth kinetics and fermentation performance. T. delbrueckii and L. thermotolerans consumed the supplemented sucrose and produced 6-7% (v/v) ethanol, while M. pulcherrima, P. kluyveri and W. saturnus only utilized the endogenous fructose and glucose, producing trace levels of ethanol. Besides, different yeasts showed different β-glucosidase activities with 22-97% reduction in isoflavone glucosides; T. delbrueckii, L. thermotolerans and W. saturnus also decreased the level of GABA in tofu whey. Endogenous volatile compounds (mainly short-chain aldehydes) in tofu whey were reduced to trace levels, but different volatile compounds were produced by different yeasts at varying levels that can contribute to the different aroma profiles of the beverages. Therefore, selection of appropriate non-Saccharomyces yeasts can serve as a new strategy to valorize tofu whey and alter the aroma profile of the beverage.