Evolution of fine structure and pasting properties in wheat starch during medium-high-temperature Daqu fermentation

Medium-high temperature Daqu is used as a starter culture for strong-aroma Baijiu. In this process, wheat starch not only serves as the primary carbon source for microbial growth but also contributes to ethanol production and aroma development during fermentation. However, how the physicochemical properties and fine structure of wheat starch change during medium-high temperature Daqu fermentation is not well understood. In this study, we examined the changes in starch molecular structure during fermentation using three wheat varieties as substrates. The total starch and amylopectin contents decreased in chuanmai 605 (CM605), zhongkemai 47 (ZK47), and mianmai 907 (MM907) after 25 days of fermentation. The amylose content slightly increased in zhongkemai 47 (ZK47) and mianmai 907 (MM907) but decreased in chuanmai 605 (CM605). The fermented starch exhibited higher solubility than native starch at 95 °C for all three varieties. Although fermentation did not alter the crystalline type pattern, but it increased the V-type starch content and slightly elevated the relative crystallinity. Fourier transform infrared analysis revealed that fermentation influenced absorption in the hydrogen-bond-related spectral region compared with native starch. In addition, fermentation reduced both the trough and final viscosity. These results provide scientific support for Daqu-optimized wheat breeding and establish practical criteria for baijiu producers in sourcing superior wheat.