Mechanism of Action of Pulsed Magnetic Field in Improving the Quality of Quick-Frozen Rice Products: A Study Based on Starch Gel Structure Regulation and Freeze-Thaw Stability

This study focuses on the effects of pulsed magnetic field (PMF) on the structure and properties of starch gels subjected to rapid freezing at −40 ℃. The results showed that during freeze-thaw cycles, the formation of large ice crystals promoted the cross-linking of starch molecules, leading to the development of more double-helix structures in both amylose and amylopectin, and causing damage to the gel network, specifically manifested as network fragmentation and the formation of porous wall structures. Repeated freeze-thaw cycles further intensified the intercellular interactions and structural damage of starch. By shortening the phase transition time, PMF-assisted freezing treatment promoted the formation of small ice crystals and mitigated the squeezing and piercing effects of ice crystals on the gel structure. Additionally, it regulated starch network reorganization, inhibited the formation of amylose and amylopectin double helix structures, reduced structural order, alleviated gel network damage, and promoted the formation of a uniform three-dimensional network, ultimately significantly improving the freeze-thaw stability of gels. Compared with the sample subjected to one freeze-thaw cycle at 0 mT (0FT-1), applying magnetic field intensities of 5 and 10 mT reduced gel hardness by 12.81% and 33.95%, respectively. Furthermore, PMF clearly preserved the structure and quality of gels subjected to multiple freeze-thaw cycles. Compared with the sample subjected to two freeze-thaw cycles at 0 mT (0FT-2), applying magnetic field at 5 and 10 mT reduced gel hardness by 5.97% and 29.35%, respectively, effectively mitigating the decline in textural quality of starch gels caused by temperature fluctuations. This study provides a theoretical basis for the application of PMF in quick-frozen rice products and offers a feasible approach to enhancing the storage stability of such foods.