Mechanism of transglutaminase and Nanyang starter co-treatment in black bean steamed bread: structural and quality improvements

This study aims to reveal the influences of applying transglutaminase (TGase) and Nanyang starter to improve the dough structure, eating quality, and frozen storage stability of black bean steamed bread. The results indicated that the combined treatment enhanced hydrophobic interactions and disulfide bonds in the dough, and increased the β-sheet and α-helix contents in the protein secondary structure by approximately 8.2% and 5.6%, respectively. These changes subsequently promoted a more uniform porous structure and improved fermentation stability. With respect to the quality of steamed bread, combined treatment improved palatability. During frozen storage, the treatment effectively mitigated moisture migration and starch retrogradation. The relative proportion of free water increased by only 0.5% compared with day 1, while starch crystallinity increased by less than 3%. Furthermore, the combined treatment reduced the protein random coil proportion from 33.51% to 18.24% and decreased the crystallinity increment from 4.35% to 2.68%, indicating enhanced structural stability during frozen storage. Correlation and mechanistic analyses confirmed synergistic gluten reinforcement and suppressed starch retrogradation. This study reveals how TGase and Nanyang starter synergistically reinforce gluten networks via enhanced non-covalent and covalent interactions, thereby stabilizing dough microstructure and slowing freezing induced quality loss, which provides a theoretical basis for the development of healthy frozen staple foods.