Development of a Vegan Soybean-Based Yoghurt Alternative Using Levilactobacillus brevis QD-1 and Saccharomyces cerevisiae as the Starter Culture for Improved Texture and Aroma Profile

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This study aimed to develop a vegan soybean yoghurt alternative using co-cultures of Levilactobacillus brevis QD-1 and Saccharomyces cerevisiae, and to evaluate their effects on textural properties, protein structure, and aroma profile of the end product.Filtered and concentrated soybean slurry was fermented using varying inoculum densities (10³-10⁵ CFU/mL) of L. brevis alone and in combination with S. cerevisiae.Visible coagulation occurred at approximately 9 h of fermentation, when pH reached 5.12-5.68.Co-cultured samples exhibited significantly improved textural attributes, including increased hardness and gumminess, and water-holding capacity, which were associated with elevated exopolysaccharide (EPS) production primarily attributable to L. brevis.In particular, the soybean yoghurt alternatives produced by co-cultured fermentation using an inoculum density of 10 4 and 10 5 CFU/mL showed the highest EPS contents (201-216 mg/L), along with increased hardness (1.48-1.58N) and gumminess (0.74-0.77N).Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis demonstrated more extensive degradation of allergenic soy proteins, including β-conglycinin and glycinin, in the co-fermented samples.Fourier-transform infrared spectroscopy indicated favourable modifications in protein secondary structure, notably an increased α-helix content, consistent with improved gel network formation.In addition, the volatile organic compound profile was characterised by shifts in the relative abundances of acetic acid, 2,3-butanediol, and phenethyl alcohol in the presence of yeast.At the highest co-culture level, ethanol content decreased to 69.55% of total volatile organic compounds, while contents of acetic acid, 2,3-butanediol, and phenethyl alcohol increased to 15.42%, 9.46%, and 1.87%, respectively.Collectively, these findings indicate that lactic acid bacteria and yeast co-fermentation may represent a promising approach to produce high-quality plant-based yoghurt with enhanced nutritional and sensory characteristics.