In this study, the permanent magnetic field (PMF) and alternating magnetic field (AMF) were applied and the effects on the microstructure and freezing parameters (nucleation temperature, freezing temperature, time through the maximum ice crystals formation zone and phase change time) were evaluated during the blueberry freezing process. The magnetic field intensities of PMF ranged from 0 to 10 mT and the peak values of AMF were 0, 0.05, 0.64 and 1.74 mT. The cooling rate and the target temperature were 4 °C/min and -30 °C respectively. As a result, the minimal average ice crystal areas were 2489 μm² for PMF (10 mT) and 1731 μm² for AMF (0.05 mT). Compared with the control group (3749 μm²), it reduced by 33.6% and 53.8%. Besides, all the freezing parameters were significantly different with PMF (p < 0.05). The nucleation temperature decreased by 5.59 °C with the intensity of 10 mT and led to a great supercooling degree. The optimal PMF intensity was 10 mT for the blueberry from the aspect of the freezing parameters and microstructure. However, the freezing parameters were not significantly different with AMF except the phase change time (p < 0.05). The heat generated by the current coils with AMF should not be ignored. When the AMF intensity increased continuously, the phase change time increased accordingly which was disadvantageous for the food freezing.

在这项研究中，应用了永久磁场（PMF）和交变磁场（AMF），并且对微观结构和冻结参数（成核温度，冻结温度，通过最大冰晶形成区的时间和相变时间）的影响是在蓝莓冷冻过程中进行评估。PMF的磁场强度为0到10 mT，AMF的峰值为0、0.05、0.64和1.74 mT。冷却速率和目标温度分别为4°C / min和-30°C。其结果，最小平均冰晶面积分别为2489微米²为PMF（10公吨）和1731微米²为AMF（0.05吨）。与对照组（3749微米相比²），分别减少了33.6％和53.8％。此外，所有冷冻参数在PMF下均存在显着差异（p <0.05）。成核温度以10 mT的强度降低了5.59°C，并导致了很大的过冷度。从冷冻参数和微观结构的角度来看，蓝莓的最佳PMF强度为10 mT。但是，除相变时间（p <0.05）外，AMF的冷冻参数没有显着差异。带有AMF的电流线圈产生的热量不容忽视。当AMF强度连续增加时，相变时间相应增加，这对于食品冷冻是不利的。