Abstract: Lactobacillus helveticus (L. helveticus), as a lactic acid bacterium with significant industrial application value, has attracted much attention due to its ability to produce exopolysaccharides (EPS) and high protein hydrolysis properties. To explore the effect of L. helveticus LH43, which has the ability to produce high-molecular-weight EPS, as an auxiliary starter on yogurt, this study investigated the gel properties and protein conformation of yogurt using texture analyzer, rheometer, scanning electron microscope, nuclear magnetic resonance, fluorescence spectrophotometer, and circular dichroism. The results indicated that the use of L. helveticus LH43 as an auxiliary starter significantly improved the texture, water-holding capacity, and rheological properties of yogurt, as well as enhanced its microstructure and flavor characteristics. Furthermore, this strain reduced the surface hydrophobicity, free thiol content, and random coil ratio of yogurt proteins while increasing the content of α-helical structure, suggesting that α-helix and random coil are the intrinsic factors contributing to the differences in fermented milk gel. In conclusion, L. helveticus LH43 can be used to improve the gel properties of dairy products and provides a new reference for the development of yogurt.

Key words: Lactobacillus helveticus, auxiliary starter culture, processing properties, protein conformation