A promising starter strain for enhanced soy milk fermentation: Improving stability and flavor by mitigating beany flavor while enriching fruity aromas

This study evaluated the potential of Lactobacillus delbrueckii subsp. bulgaricus ( L. bulgaricus ) M-58, isolated from naturally fermented sour yak milk in Mongolia, as a starter culture for soy milk fermentation. It compared the performance of L. bulgaricus M-58 to that of the commercial starter culture 904-vege, assessing fermentation efficiency along with stability, metabolomic profiles, and sensory qualities of the resultant fermented soy milks over 21 days of storage. Key parameters included the TURBISCAN stability index, rheological properties, texture, viscosity, water-holding capacity, and volatile/non-volatile metabolite profiles, which were analyzed via gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. Soy milk fermented with L. bulgaricus M-58 exhibited superior stability, as evidenced by lower TURBISCAN stability index values, enhanced gel structure formation, and improved texture measurements, including water-holding capacity and consistency. Metabolomics analyses revealed significant reductions in beany flavor-associated compounds, including hexanal, hexanol, phenylacetaldehyde, linoleic acid, and linolenic acid. Moreover, there was an increase in succinic acid, which mitigated the beany flavor. Notably, levels of desirable volatile metabolites, such as phenylethyl alcohol and acetophenone, were elevated, imparting appealing fruity, citrus, and rose aromas. Additionally, L. bulgaricus M-58 significantly degraded indigestible oligosaccharides (raffinose and stachyose) and increased riboflavin, contributing to improved nutritional value. The findings highlight L. bulgaricus M-58 as a promising candidate for producing high-quality, consumer-friendly fermented soy milk with enhanced sensory and functional properties. Future research should explore dynamic changes during fermentation, optimize processing conditions, and assess scalability for industrial applications, supporting innovation in plant-based foods and sustainable nutrition.