Molecular interaction mechanisms of Lactobacillus helveticus KLDS1.8701 on construction of yogurt gel network, transformation of milk protein conformation, and formation of characteristic flavor.

The excellent properties of Lactobacillus helveticus KLDS1.8701 (L. helveticus KLDS1.8701) make it a potential auxiliary starter strain. This study aimed to investigate the effects of L. helveticus KLDS1.8701 on yogurt and the mechanisms underlying these effects. The results indicated that L. helveticus KLDS1.8701, when used as an auxiliary starter, significantly shortened fermentation time, improved the textural and rheological properties of yogurt, and enhanced its viscosity and water-holding capacity. Observations of the yogurt microstructure revealed that the addition of L. helveticus KLDS1.8701 resulted in the formation of a more compact network structure, which correlated with its ability to produce extracellular polysaccharides. Furthermore, when used as an adjunct starter, L. helveticus KLDS1.8701 significantly reduced surface hydrophobicity and free thiol content, and altered the proportions of its secondary structure. The content of all secondary structural units except β-sheet significantly decreased. These changes in protein structure may be the primary factors contributing to variations in the gelation of the yogurt. Finally, L. helveticus KLDS1.8701, serving as an auxiliary starter, exerted a notable influence on the sensory characteristics of yogurt. It not only substantially increased the levels of 2-heptanone and 2-nonanone in yogurt but also introduced a distinct fruity aroma derived from heptanethioic acid, S-methyl ester. The unique flavor imparted by L. helveticus KLDS1.8701 enhanced the yogurt's aroma and overall flavor quality. Therefore, the addition of L. helveticus KLDS1.8701 enhances the fermentation of yogurt, making it a potentially valuable adjunct starter with commercial potential.