Effects of static magnetic field-assisted freezing on freezing characteristics and quality changes of Hypophthalmichthys nobilis

The low efficiency and the formation of irregularly shaped ice crystals in traditional freezing equipments lead to severe quality degradation in frozen aquatic products. Consequently, it is urgent to improve the exploration and practical application of novel assisted freezing technologies. To investigate the effects and underlying mechanisms of static magnetic field (SMF)-assisted freezing on the quality of Hypophthalmichthys nobilis fillets during frozen storage, we employed SMF of different intensities (0, 6, 10 mT) to assist the freezing process of H. nobilis. We measured the freezing curves to explore the differences in freezing characteristics, and indicators such as thawing loss, muscle microstructure, and moisture distribution were evaluated. Then we detected the oxidative indicators (Carbonyl groups, sulfhydryl groups, disulfide bonds, dityrosine, and Schiff base) and endogenous fluorescence to characterize myofibrillar protein (MP) oxidation. Results indicate that SMF significantly shortened phase transition time during freezing (p<0.05), forming finer and more uniformly distributed ice crystals. At the end of storage, the 6 mT SMF treatment reduced thawing loss of fish by 8.44%, with over 90% immobilized water content, and significantly decreased malondialdehyde accumulation and yellowness (p<0.05). Besides, this SMF intensity favored maintaining lower content levels of carbonyl groups, disulfide bonds, dityrosine, and Schiff base in MP, while preserving higher sulfhydryl content and effectively reducing MP structural unfolding. In summary, the phase transition time of H. nobilis decreases with increasing SMF intensity during freezing, with an intensity of 6 mT demonstrating the better effect on improving frozen storage quality.