Comprehensive comparison of physicochemical properties, volatile flavor compounds and functional activities of double protein yogurt with different soymilk and cow milk additions.

With the rising consumer demand for functional dairy products, dual-protein yogurts combining animal and plant proteins offer a promising strategy to improve nutrition and health benefits. This study prepared five types of double protein yogurt with varying soymilk additions (0 %, 25 %, 50 %, 75 %, and 100 %) in cow milk. Then, the effects of soymilk additions on the physicochemical properties, volatile flavor compounds, antioxidant properties, angiotensin-converting enzyme (ACE) inhibitory activity, and in vitro digestive properties were investigated. The results showed that the soymilk double-protein yogurt with 25 % added soy milk exhibited the best characteristics, including the highest protein (3.67 %), fat (3.46 %), total sugar content (7.69 %), and Streptococcus thermophilus count (9.5 × 106 CFU/g) as well as a dense microstructure. The percentage of soymilk had a significant effect on the volatile flavor profile. Compared with yogurt fermented from a single ingredient, dual-protein yogurt has a more fragrant aroma. Higher levels of hexanal (the primary source of soy flavor, 67.56 μg/g) were detected in yogurt with more than 50 % soymilk addition. The antioxidant activity of soymilk double-protein yogurt increased significantly with soymilk addition to the system. The gastric digestion stage is critical for releasing antioxidant actives in yogurt. Dual-protein yogurt with 25 % soymilk addition showed the highest ACE inhibition after oral digestion (66.70 %), significantly increasing to 85.75 % after gastric digestion. These findings emphasize the potential of combining plant and animal proteins and provide new insights into developing a functional, nutritious dual-protein yogurt.