Abstract: This study was conducted in order to investigate the effect of Lactobacillus helveticus LH43, which has the ability to produce high-molecular-mass extracellular polysaccharides, as an auxiliary starter on the gel properties and protein conformation as determined using a texture analyzer, a rheometer, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), fluorescence spectrophotometry and circular dichroism (CD) spectroscopy. The results showed that the application of L. helveticus LH43 as an auxiliary starter significantly enhanced the textural properties, water-holding capacity (WHC) and rheological characteristics of yoghurt and improved its microstructure and flavor characteristics. Additionally, the strain reduced the surface hydrophobicity, free sulfhydryl content and relative content of random coil of yoghurt proteins, and increased the relative content of α-helical structures, confirming α-helix and random coil to be intrinsic factors leading to differences in the gel properties of fermented milk. In conclusion, L. helveticus LH43 can be used to improve the gel properties of dairy products, and this study provides a new reference for improving the fermentation process of yoghurt.

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