Quality evaluation of soy yogurt fermented by Saccharomyces boulardii CNCM I-745 and Lactiplantibacillus plantarum KU985432 co-culture

The growing demand for plant-based dairy alternatives has driven interest in improving the quality of soy yogurt. This study investigated the impact of a co-culture of Lactiplantibacillus plantarum KU985432 and Saccharomyces boulardii CNCM I-745 on the microbial, physicochemical, antioxidant, and sensory properties of soy yogurt. Different inoculum ratios were evaluated, with the 1:1 (v/v) ratio (SY1) demonstrating a synergistic effect, significantly multiplying the viability of both microorganisms to 10 log CFU/mL after 24 h. Co-fermentation significantly (P < 0.05) enhanced the total phenolic content and antioxidant activity (DPPH and ABTS⁺ assays) compared to single-strain fermentations. The optimized SY1 co-culture was then used to produce plain and strawberry-flavored yogurts. The resulting strawberry-flavored yogurt exhibited potent physicochemical properties, characterized by significantly higher total solids (16.92%) and carbohydrate content (10.83%), an enhanced water-holding capacity (94.54%), and an improved texture profile, as reflected by increased hardness (2.1 N), cohesiveness (0.61), gumminess (1.28 N), and a chewiness of 1.4 (N*mm). Sensory evaluation revealed that the strawberry-flavored yogurt had significantly higher scores on a 9-point scale for appearance (7.13), aroma (6.2), and overall acceptability (7.13), with reduced astringency (1.8 on a 5-point intensity scale). Throughout 14 days of refrigerated storage, both yogurts maintained high probiotic viability (> 10⁷ CFU/mL), stable phenolic content, and potent antioxidant activity. This study confirms that co-fermentation with L. plantarum KU985432 and S. boulardii CNCM I-745 is a highly effective strategy for producing a nutritious, sensorily appealing, and commercially viable probiotic soy yogurt.