Melatonin regulates protein structures of wheat under shading for cookie crack ratio and digestibility modifications.

The crack ratio and nutritional value of cookies depend on wheat protein structures, yet how melatonin modifies these attributes under shading remains unclear. This study evaluated the effects of melatonin (200 μmol L-1) on protein structure and cookie-making quality in shaded wheat. Under shading, melatonin increased glutenin, gliadin, total protein, and small polymeric protein content, and raised β-sheet and α-helix proportions by up to 14.4% and 13.2%, respectively, strengthening non-covalent interactions into a more cross-linked gluten network. Melatonin also elevated sulfur-containing and aromatic amino acids, improving nutritional value and digestibility. A SegFormer-based machine learning model showed melatonin reduced the cookie crack ratio by 18.8-30.7% and improved homogeneity. Protein content, γ-gliadin, and small polymeric proteins governed the crack ratio, whereas digestibility was primarily associated with small polymeric proteins. Collectively, melatonin regulates crack ratio and digestibility by modulating amino acid profiles and protein structures, offering a promising approach to enhance cookie-making quality.