Effects of Co-Fermentation with Lactobacillus and Yeast on the Structural and Physicochemical Properties of Millet Starch

Based on the previously screened high-performance strain Lactobacillus LP707, this study systematically investigated the effects of its co-fermentation with yeast on properties of millet starch. By comparing starch samples from unfermented, yeast-only fermented, Lactobacillus-only fermented and co-fermented treatments, it was found that co-fermentation reduced the amylose content of millet starch to 17.45% and shifted the molecular weight distribution toward lower values. Scanning electron microscopy revealed more pronounced surface erosion features on the co-fermented starch granules. X-ray diffraction and Fourier-transform infrared spectroscopy confirmed that co-fermentation did not alter the A-type crystalline pattern of starch; however, the short-range ordered structure ratio (1.45), relative crystallinity (20.78%), and gelatinization enthalpy (7.32 J/g) were significantly reduced, indicating dissociation of ordered structures. Pasting property analysis showed that the final viscosity and setback value of co-fermented starch decreased significantly. Low-field nuclear magnetic resonance analysis of water distribution indicated an increased proportion of free water with reduced mobility in the co-fermented starch gel. In vitro digestion confirmed higher hydrolysis rates and increased rapidly digestible starch content in co-fermented starch. In summary, co-fermentation with Lactobacillus LP707 and yeast more effectively modified properties of millet starch, providing a theoretical foundation for targeted functional improvement through microbial co-fermentation technology.