Effects of ripening conditions on protein conformation and quality of frozen tofu prepared by different coagulants

This study systematically investigates the effects of ripening conditions on protein conformation and quality of frozen tofu prepared with different coagulants (CaCl 2 , CaSO 4 , and MgCl 2 ). Tofu samples were frozen at -3°C and -21°C for 1–21 days, and characterized by their texture, water-holding capacity (WHC), thawing loss, rheological properties, moisture distribution, and protein structure. The results showed that sequential ice recrystallization during ripening enlarged pores and enhanced protein–protein interactions with increasing hardness and elasticity. Compared to -21°C for 21 days, -3°C at the same duration yielded significantly higher hardness increases. WHC decreased initially and then stabilized, while the thawing loss first increased and then decreased with prolonged ripening. The development of an increasingly homogeneous and dense gel network resulted in a sponge-like honeycomb structure. Protein oxidation, an increase in disulfide bonds, and enhanced hydrophobic interactions acted synergistically to reinforce the gel network via both covalent cross-linking and non-covalent aggregation. The analysis of structure indicated extensive protein unfolding, characterized by an increase in β-sheets and a decrease in α-helices, which facilitated molecular aggregation and gel formation. Optimal ripening conditions were critical to developing a stable honeycomb structure and improving product quality. These findings provide insights for industrial frozen tofu production. • -3 °C for 21 days markedly boosts frozen tofu hardness and elasticity. • Ice recrystallization drives protein cross-linking, forming uniform honeycomb. • 11S aggregation and increased disulfide bonds underlie texture enhancement. • Optimized ripening offers industrial control for frozen tofu quality.