Effects of fish skin collagen peptide and freezing on structure, rheology, water distribution, and digestibility of starch within wheat dough

Fish skin collagen peptides (FSCP) are primarily sourced from fish processing by-products and exhibit notable bioactivity and superior functional characteristics. The effects of FSCP (0–2.0%, w/w, based on flour weight) on the structure, rheological properties, water distribution, and in vitro digestibility of starch within wheat dough during freezing were systematically investigated. The addition of FSCP reduced the R 1047/1022 ratio from 1.35 ± 0.26 to 0.99 ± 0.21 and relative crystallinity from 31.08 ± 0.56% to 25.21 ± 0.14%. Low-field nuclear magnetic resonance analysis demonstrated that FSCP inhibited water migration and reduced the proportion of free water, thereby restricting starch chain mobility. Correspondingly, both the onset temperature and peak temperature of gelatinization increased, indicating enhanced thermal stability of the starch. Scanning electron microscopy observations further revealed that FSCP formed a protective layer on the surface of starch granules, thereby alleviating freeze-induced structural damage. Rheological analysis showed that FSCP increased the storage modulus, indicating the formation of a more stable starch network. Consequently, the rapidly digestible starch content decreased by up to 22.31 ± 0.36% after 6 weeks of freezing, with 1.5% FSCP identified as the optimal addition level. This study establishes a mechanistic relationship among water immobilization, starch reassociation, and digestibility and provides a novel strategy for improving the quality and nutritional functionality of frozen starch-based foods. Future work should verify the efficacy of FSCP in frozen dough products (such as frozen steamed breads and dumplings) and test the cost-effectiveness of the antifreeze additive.