Effect of magnetic field treatment on the softening of strawberries during cold storage

This study investigated the effects of a 5 mT magnetic field (MF) treatment on strawberry storage using conventional refrigeration (CR) as a control. The effects of MF on the main qualities of strawberries, including firmness, color, weight loss, cell wall components, water distribution, cell wall structure, degradative enzyme activity, and related gene expression levels, were investigated during storage. MF treatment reduced strawberry firmness loss by 55.76 %, weight loss by 57.14 %, and color loss by 41.12 % and effectively alleviated surface spoilage compared with CR at 15 d. Low-field nuclear magnetic resonance analysis showed that the free water content of strawberries in the MF group was 17.93 % higher than that in the CR group. Transmission electron microscopy results indicated that MF better maintained the structural integrity of strawberry cell walls. MF significantly inhibited the expression of cell wall-degrading enzyme-related genes (FaPG, FaPME, FaPL, and FaEG) in strawberries. This inhibition slowed the elevation of polygalacturonase (PG), pectin methyl esterase (PME), pectin lysin (PL), and endoglucanase (EG) activities. MF preserved cell wall matrix (CWM), ionic pectin (ISP), covalent pectin (CSP), hemicellulose (HC), and cellulose (CE) contents in strawberries. Simultaneously, it attenuated the accumulation of water-soluble pectin (WSP) and inhibited the degradation of polysaccharide fractions during storage. In summary, MF treatment is an effective non-thermal preservation technique with potential applications in the food industry.