Effect of Polygonatum cyrtonema Flour Addition on the Rheological Properties, Gluten Structure Characteristics of the Dough and the In Vitro Digestibility of Steamed Bread

flour (PCF) into wheat flour on dough functionality and steamed bread quality. The results show that PCF enhanced dough hydration, rheology, and protein network stability through hydrophilic and non-covalent interactions, particularly hydrogen bonding. At the optimal level, steamed bread demonstrates improved specific volume, elasticity, and cohesiveness, accompanied by reduced hardness and chewiness, with hardness decreasing by 29%, chewiness by 25.80%, and gumminess by 26.30%. Microstructural analyses have confirmed enhanced water retention, strengthened gluten matrices, and favorable secondary structure transitions. The ultraviolet visible absorption spectroscopy and fluorescence spectroscopy analyses revealed that PCF enhanced the interactions between proteins and starch, accompanied by a red shift and decreased fluorescence intensity, indicating a more compact protein conformation. These findings suggest that PCF regulates protein secondary structures through hydrogen bonding and hydrophobic interactions, thereby stabilizing the gluten network. PCF supplementation boosted antioxidant activity and modulates starch digestibility; at a 10% substitution level, resistant starch (RS) decreases from approximately 60% in the control to 34%. This reduction indicates that PCF disrupts the integrity of the starch protein matrix, increasing amylase accessibility to starch granules and thus promoting starch hydrolysis. Incorporating 4% PCF in the formulation enhances both the technological performance and nutritional quality of the product while maintaining its overall integrity. These findings highlight the dual role of PCF in improving technological functionality and nutritional attributes. PCF emerges as a promising natural fortification ingredient for steamed bread, offering quality enhancement and additional health value.