The Leavening Agents Affect the Protein-Starch Matrix Formation and In Vitro Starch Digestibility of Chinese Steamed...

The present study investigates the influence of different fermentation starters-sourdough and commercial yeast-on the textural characteristics, structural features, and in vitro starch digestibility of Chinese steamed bread (CSB). Two commercial yeast strains (CD0672 and CD0731) and sourdoughs from distinct regions in China (SDJZ-Shandong Jiaozi and SXJZ-Shaanxi Jiaozi) were utilized. The sourdough fermented SXJZ-CSB exhibited the highest hardness (15.94 N/cm²), chewiness (1558.39), and total phenolic content (0.63 mg GAE/g). Compared to yeast-CSB, sourdough fermentation altered the secondary structure of protein, resulting in a significantly higher proportion of β-turns in sourdough-CSB. Principal component analysis (PCA) further confirmed that fermentation type significantly affects protein structure, with sourdough-CSBs clustering separately from yeast-CSBs. Moreover, in vitro digestion assays using both intestinal (ID) and gastrointestinal (GID) models revealed significantly lower starch digestion in sourdough-CSBs, likely due to a denser protein-starch matrix that hindered enzymatic breakdown. These findings suggest that sourdough fermentation influences the structural properties of CSB, contributing to reduced starch digestibility and potentially lowering glycemic responses.