Protective effects of scallop mantle protein peptides on the freeze-thaw stability and antioxidant properties of frozen dough and steamed bread.

In this study, scallop mantle, a by-product of scallop processing, was used as the raw material to prepare scallop mantle protein peptides (SMPP-4, molecular weight < 1 kDa) through enzymatic hydrolysis combined with ultrafiltration. The peptide was characterized for its physicochemical properties, antioxidant and cryoprotective functional properties, and its quality-improving effects on dough and steamed bread subjected to repeated freeze-thaw cycles were systematically explored. Amino-acid composition results showed that SMPP-4 was rich in hydrophobic and aromatic amino acids, with a high proportion of glycine (Gly) among polar amino acids. This peptide possessed 56.88% β-turn secondary-structure content, and exhibited strong in-vitro antioxidant activity as well as thermal hysteresis activity (THA) of 2.42 °C. After five freeze-thaw cycles, the addition of 2% SMPP-4 significantly inhibited water migration in the dough and improved its rheological properties, protein secondary and tertiary structures, thermal stability, and microstructure. It also increased the relative content of disulfide bonds and hydrogen bonds, while decreasing the levels of carbonyl groups, free sulfhydryl groups, ionic bonds, and hydrophobic interactions. Furthermore, the incorporation of 2% SMPP-4 optimized the internal structure of steamed bread, improved its whiteness and textural properties, and strengthened its antioxidant capacity. In conclusion, SMPP-4 serves as a natural modifier that effectively alleviates quality deterioration of flour products caused by freeze-thaw treatment, and exhibits promising application potential in the frozen flour food industry.