Effect of mechanical and ultrasound treatments on the physicochemical properties and bacterial activity of fermented whole soy milk-based products

The increasing demand for plant-based dairy alternatives highlights the need to improve the texture, stability, and microbial performance of soy milk yogurts. Using whole soy milk that retains okara enables direct valorization of soybean residue, eliminating okara as a by-product and reducing waste generation in soybean processing. Therefore, the objective of this study was to investigate the effect of mechanical and ultrasonic treatments on the physicochemical properties and bacterial activity of fermented dairy products made from whole soy milk containing okara (WSM). For this purpose, standard soy milk without okara (SSM) and WSM were prepared and used as references. The WSM was subjected to high-shear mixing (HSM), ultrasound (US), a combination of HSM and US (HSM+US) or a combination of HSM and high-pressure homogenization (HSM+HPH). All samples were fermented using a mixture of Streptococcus thermophilus and Lactobacillus bulgaricus . The results showed that WSM reduced the time required to reach pH 4.5 by 32% and enhanced the viability of S. thermophilus , maintaining a cell count above 10⁷ CFU/g at the end of cold storage. WSM also reduced syneresis by 40% and increased hardness by 613% after HSM+US and by 594% after US compared to SSM. These findings suggest that stable soy milk-based yoghurt products with enhanced properties can be produced by combining WSM with mechanical or ultrasonic treatments. • Okara in soymilk accelerates fermentation and enhances S. thermophilus viability. • Mechanical/ultrasonic treatments improve texture, gel structure, and reduce syneresis. • Whole soymilk limited the fall in pH during refrigerated storage. • Approach promotes stable, yogurt-like plant-based products with functional fibers. • Strategy enables energy-efficient, mild processing and supports sustainable scale-up.