Effect of Short-Term Static Magnetic Field Pretreatment on Cold-Storage Quality and Phenolic Metabolism of Blueberries

Blueberries are widely consumed due to their richness in nutrients, yet they are also prone to quality deterioration after being harvested, even at cold temperatures. Non-thermal physical technology is an important auxiliary method worth considering for maintaining the quality of this fruit while refrigerated. In this study, a static magnetic field (SMF) was applied as a complementary pretreatment strategy prior to cold storage of blueberries. The optimal SMF parameters were identified as 5 mT exposure for 12 h, as this significantly retarded decay and softening. The contents of ascorbic acid, total polyphenols, flavonoids and proanthocyanidins were elevated by 20.0%, 17.7%, 23.9%, and 9.1%, respectively. Concurrently, DPPH (1,1-diphenyl-2-picrylhydrazyl) radical-scavenging capacity, catalase (CAT), and superoxide dismutase (SOD) activity markedly improved. Targeted metabolomic analysis revealed that SMF pretreatment significantly regulated polyphenol metabolic pathways and redirected polyphenol biosynthesis toward more stable and functional compounds, including three hydroxycinnamic acids, quercetin, dihydromyricetin, glycosylated hesperetin, and acylated delphinidin derivates. The synergistic effect of these SMF-elevated phenolics and the reinforced antioxidant system preserved the overall cold-storage quality of blueberries. These findings underscore the potential of SMF pretreatment as an effective physical technique for reducing postharvest blueberry losses.