Exploring the Potential of Torulaspora delbrueckii, Starmerella bacillaris, and Saccharomyces cerevisiae as a Probiotic Starter for Craft Beer Production

This paper explores the broad probiotic and functional properties of two non-<i>Saccharomyces</i> strains (MI120 and MI125) and one <i>Saccharomyces cerevisiae</i> BB06 strain (as a reference probiotic). <i>Torulaspora delbrueckii</i> MI120 and <i>Starmerella bacillaris</i> MI125 were identified via 5.8S rDNA sequencing. All the strains survived well in simulated gastrointestinal conditions and had strong antioxidant activity (>68%). <i>S. bacillaris</i> MI125 excelled in antimicrobial activity against Gram-positive and Gram-negative bacteria. <i>S. bacillaris</i> MI125 and <i>Sacch. cerevisiae</i> BB06 resisted all the tested antibiotics. No strain displayed hemolytic behavior. The freeze-dried yeast strains achieved survival rates between 76.62% and 93.38%. Based on our physiological characterization analysis (carbon assimilation, ethanol tolerance, acetic acid and H₂S production, temperature and low pH tolerance, enzymatic pattern, and killer phenotype), all the strains showed interesting attributes, with <i>Sacch. cerevisiae</i> BB06 fermenting vigorously in malt extract medium. Beer fermented with <i>T. delbrueckii</i> MI120 had the highest phenolic content (96.02 μg GAE·mL^-1) and antioxidant activity (90.43%), matching commercial <i>Sacch. cerevisiae</i> US-05 in sensory traits such as taste and aroma. However, after two months in bottled beer, the yeast viability decreased to 2-3 log CFU·mL⁻¹. The pilot brewing and the assessments of the strains' technological, physico-chemical, and sensorial properties confirmed their suitability for industrial brewing. Overall, <i>T. delbrueckii</i> MI120 emerges as a promising brewing strain, and <i>S. bacillaris</i> MI125 is a potential probiotic.