The Effect Of Electromagnetic Field On Cell Freezing Properties

In recent decades, the rapid development of wireless technology made it penetrated into all aspects of human life and production, along with it came the influence of electromagnetic fields(EMF) on organisms, which gradually captured many reserchers’ attention, research on the biological effects of electromagnetic noted that EMF has impacts on a number of physiological activities of organisms. However, in the food refrigeration areas, the traditional way to preserve food can cause damage to its quality, vitrification preservation may have many advantages than traditional freezing process which is featrued with phase change, but actually it’s too difficult to achieve vitrification. In view of the fact that most of the food materials are biological materials, we propose that combine the electromagnetic biological effects with food freezing process to explore the role of EMF on phase transition of food material freezing process.In this paper, Helmholtz coils magnetic field(MF) which was self-designed was applied to the freezing process of onion and three other fruit and vegetable tissues, during the freezing process a cryogenic microscope Olympus BX51 which had a camera with it was used to take microscopic photos for the whole process, the purpose of the above operations was to explore the influences of different forms and intensities of EMFs on pattern and size of ice crystal as well as morphology and volume of cell during the phase change stage of fruit and vegetable tissues freezing process. In this experiment, fruit and vegetable tissues were frozen with the Linkam BCS196 cryogenic-stage that cooling biological samples with liquid nitrogen, the temperature accuracy of the cooling process could be up to 0.01℃; the forms of magnetic fields used in this experiment were DC magnetic field and AC magnetic field, five groups of MF strengths were: 4.6Gs, 9Gs, 18 Gs, 36 Gs, 72Gs; in view of the importance of water and aqueous solution in phase transition of cell freezing process, the experiment of water and 0.9% KMn O4 aqueous solution under the above conditions was studied as well. Through the above experiments we obtained a lot of image data.The study found:I. Effect of magnetic field on the freezing process of water and aqueous solution1. The intervention of MF in the freezing process could reduce the supercooling degrees of water and aqueous solution to some extent. The supercooling degrees under the five groups of MFs: 4.6Gs, 9Gs, 18 Gs, 36 Gs, 72 Gs decreased by 1.62 ℃, 1.68 ℃, 1.65 ℃, 2.23 ℃, 2.55 ℃ respectively, compared to the control group;2. Statistical results showed that, in the phase transition stage the ice crystal sizes of the MF groups were smaller compared to the control group, and the average ice crystal sizes of water and KMn O4 solution in the MF groups were about 67% and 76% that of the control group respectively.II. Effect of MF on onion, carrot, cucumber, zucchini and other fruits and vegetables freezing process1. The intervention of MF made the ice patterns of the phase transition tended to like fog and sand, while in the control group, the shape of the ice crystal tended to be much larger and like blades or blocks;2. The supercooling degrees in MF groups were lower than that of the control group, the phase change process had been delayed. Under the five different MF strengths, the four fruits and vegetables supercooling degrees all decreased compared to the control group. In general, the decrements of supercooling degrees decreased as the MF strengths increased;3. The time spans of phase transition processes in the MF groups were shortened. Under the five different MF strengths, the phase transition time spans of four fruits and vegetables were shortened compared to that of the control group, respectively;4. The author proposed a new concept, "two dimension cell maintainable ratio ζ", based on cell deformation level, which was used to rank the different freezing methods. This newly proposed indicator could be obtained by using Auto CAD software to edit the microimages received from the camera of the microscope. Results showed that the ζ values got from MF groups were generally greater than that of the control group. However, the variation laws of the ζ values versus MF strengths didn’t fit each other.To sum up, through the experiments of water and aqueous solutions, fruit and vegetable cells frozen in the MF, conclusions can be drawn that, MFs can postpone the phase change process, inhibit the formation of ice crystals and have a better performance in protecting cell structure, compared to the control group, which mechanism may be explained as follows, water molecule and its cluster has the diamagnetism, when they’re in the magnetic field, they produce additional magnetic moments(AMM), while, these AMMs may interrupt their own random thermal motion(also called Brownian motion) which can cause the phase transition nucleation barrier to increase and the flowability to decrease, thus the supercooling degrees become lower and the ice crystal sizes reduce. These effects mentioned above proved that the MF-assisted freezing process compared to traditional freezing process may have the advantages of reducing damage extent to fruit and vegetable cells caused by ice crystals of freezing process and keeping the original quality and flavor of the fruit and vegetable as much as possible. Consequently, this technique may have a considerable research value and application value.