Reduced Digestibility of Maize Starch in Freeze-Thaw Cycles: Mechanistic Insights into the Role of Fish Scale Peptides

Freeze-thaw (FT) cycles cause structural deterioration of maize starch (MS), accelerating starch digestibility and glycemic responses. This study investigated whether crimson snapper fish scale peptides (FSP) could modulate MS structure to reduce digestibility during FT cycles. FSP inhibited ice recrystallization and preserved bound water while suppressing free water increase. After three FT cycles, amylose content in MS-8FSP remained at 24.17% while 28.17% in MS, while Mw was unchanged. Hydrophobic interactions dominated FSP-starch binding, though hydrogen bonds weakened during freezing. SEM, XRD and DSC showed that MS-8FSP formed compact lamellar networks, with relative crystallinity increasing to 5.29% and Peak II enthalpy recovered after three FT cycles. Consequently, FSP reduced rapidly digestible starch and estimated glycemic index (MS-8FSP: 69.22; MS: 92.06). Pearson correlation analysis revealed that FSP binding and non-covalent bonds were negatively correlated with rapidly digestible starch and estimated glycemic index, whereas water permeability was positively correlated with both. In vivo, MS-8FSP significantly attenuated postprandial glucose responses in mice, with lower AUC than MS across all FT cycles. These findings suggest that FSP enhances starch FT stability and reduces digestibility, offering a promising ingredient for frozen starch-based foods with reduced glycemic potential.