Impact of Saccharomyces boulardii Cell Residues on Lactobacillus rhamnosus GG Growth and Functional Properties in a Sorghum-Based Probiotic Beverage

Probiotic viability in plant-based beverages is often hindered by limited nutrient availability. This study investigated the potential of Saccharomyces boulardii cell residues to enhance Lactobacillus rhamnosus GG growth and functional properties in a sorghum-based beverage. Three fermentation strategies were compared: yeast-only (SYD), bacteria-only (SBD), and sequential two-stage fermentation (SYBD), where heat-inactivated yeast residues preceded bacterial inoculation. Microbial counts, pH, reducing sugars, phenolic content, and antioxidant activity were analyzed. The SYBD treatment yielded the highest L. rhamnosus viability (10.68 Log CFU/mL), surpassing SBD (10.26 Log CFU/mL) and SYD (6.33 Log CFU/mL yeast), attributed to released metabolites (e.g., free amino nitrogen) and pH modulation. SYBD also retained superior phenolic content (32.01 mg GAE/L) and antioxidant activity (152.4 mg BHT eq./L) compared to SBD, suggesting yeast-derived bioactivity. Notably, sequential fermentation produced a low-calorie beverage (10.69 kcal/100 mL) with balanced acidity and reduced sugar content (0.07%). These results demonstrate that S. boulardii residues optimize probiotic growth and functional properties in sorghum beverages, offering a novel strategy for nutrient-rich, synbiotic functional foods. Further research should explore strain-specific interactions and scale-up feasibility.