Non-monotonic effect of starch content on protein digestion in wheat noodles mediated by protein network structural...

Precise control of nutrient digestion through food matrix design remains a central challenge in modern food science. This study investigated the non-linear regulatory effect of starch content on protein digestion by evaluating protein digestibility and free amino acid release in wheat noodles, along with the underlying mechanism. Results demonstrated a non-linear relationship between starch content and protein digestibility. At 78.5% starch, the protein digestibility increased to a maximum value (70.00), beyond which content it plateaued. In contrast, amino acid release reached a maximum of 124.23 mg/g at 74.50% starch, then declined to 102.00 mg/g at 80.50% starch. The improvement in protein digestibility was associated with higher proportions of SDS-soluble protein and β-turn, as well as increased exposure of enzymatic hydrolysis sites-particularly tryptophan and tyrosine residues. However, when starch content exceeded 74.50%, the shift toward buried disulfide conformations (increased g-g-g), along with CLSM imaging and an increased protein width,collectively indicated the likely formation of protein self-aggregates. This structural reorganization is proposed to restrict enzyme access to proteolytic sites, explaining the reduction in final amino acid release despite the maintained high protein digestibility. Consequently, a moderate starch content (74.50%) maximizes amino acid release by preventing protein excessive aggregation. This finding provides practical guidance for designing staple foods tailored to specific nutritional needs, such as promoting rapid amino acid absorption for the elderly.