In order to explore the effect of DC electromagnetic field of different field strengths on the shape and size of cells and ice crystals during the freezing phase transformation process of plant tissue cells

the third layers of onion cut into squares of 0.5 cm×0.5 cm were studied. Put the onion slices on the cold platform and the cooling rate of the experiment was: 10 ℃/min before 0 ℃

3 ℃/min after 0 ℃

and the final temperature was﹣25 ℃

the DC magnetic field strengths were 0Gs (the control group)

4.6 Gs

18 Gs

36 Gs

72 Gs respectively. In the experiment

the changes of morphology of the cells and ice crystals under different strengths were observed

and the index of "two-dimensional cell retention rate ζ" was put forward to evaluate fruit and vegetable cells’ freezing effect. AutoCAD software was used to calculate the micrograph and the value of ζ. The results show that the magnetic field assisted freezing of the onion cells can make the formation of ice crystals tend to atomization and sand grains

which can inhibit the growth of ice crystals

thus reduce the size of the ice crystals

and it will also be more conducive to maintain the original cell morphology and decrease the cell damage rate. With the increasing of the magnetic field strength

phase transformation time of the onion cells decreases

supercooling degree decreases gradually

but it is always higher than that of non magnetic field.