The Combined Effect of Corn Zein and Buckwheat Flour on the Rheological, Microstructural, Physicochemical, and Nutritional Properties of Gluten-Free Bread

The development of structurally stable and nutritionally enhanced gluten-free bread is a major technological challenge due to the absence of a gluten network. This study investigates the role of zein, a hydrophobic corn prolamin, in green buckwheat dough systems and its impact on bread properties. Zein was extracted from corn gluten and incorporated at 0, 10, 20, and 30%. Zein incorporation significantly modified starch–protein interactions, promoting a composite matrix with enhanced thermomechanical stability. The 20% zein formulation showed optimal performance, with increased peak viscosity, higher C2 and C3 torque values, improved starch gelatinization, and a more cohesive microstructure. The scanning electron microscopy analysis confirmed a continuous protein–starch network, with the highest elasticity and cohesiveness (0.85 and 0.57, respectively). The optimized formulation maintained functional value and reduced the conditional glycemic index. In the 20% zein formulated sample, the rapidly digestible starch fraction decreased from 48.1% to 41.6%, while slowly digestible and resistant starch increased from 22.4% and 7.8% to 26.3% and 10.4%, respectively. Overall, zein enrichment effectively compensates for the absence of gluten, resulting in improved bread quality and controlled starch digestibility. These findings provide new insights into protein–starch interactions in gluten-free systems and support the application of zein as a functional structuring agent in pseudocereal-based bakery products.