Novel Technology for Cryopreservation of Food by Utilizing Active Enhancement of Supercooling due to Microwave Irradiation

冷冻可以减缓或停止一些保存食物的生物反应。同样，冷冻对保持食物的味道也是致命的。在冷冻过程中，细胞内外结冰、渗透水透过细胞膜、细胞变形等行为在微观上发生，并与蛋白质的滴落和变性有关。主动提高过冷度的方法是食品超低温保存的有效方法之一。本课题的目的是研究微波辐射对食品冷冻过程中超冷和结冰的影响。在2.45 GHz微波辐射下，对甘油溶液和苹果组织进行冷冻处理。用冷冻显微镜对冷冻细胞的超冷度进行了测量和形态观察，结果表明，微波具有两个方面的作用：一是增强过冷，二是依赖微波功率释放过冷。尤其是在液氮浸泡冷却的情况下，随着微波功率的增加，冷却面附近的冰晶尺寸减小。因此，微波、辐射和快速降温相结合被认为是减少冻害的一种途径。对于组织中的核心区，由于微波引起的加热效应增大，导致局部降温速率降低，因此微波对冰晶尺寸的影响减弱。因此，微波辐照的尺寸效应是需要考虑的重要因素。

Freezing can slow down or stop some biological reactions for preserving food. It is also true that the freezing is lethal to keeping the taste of food. During freezing, the extra-and intra-cellular ice formation, osmotic water permeation through cell membrane, deformation of the cell and other behavior occur at microscale and they bring serious injuries connecting to drip and denaturation of protein.A method to actively enhancing the supercooling is one of promissing technique for cryopreservation of food The object of this project was to study the effects of microwave irradiation on supercoling and ice formation during freezing of food. In the experiments, glycerol solution and apple tissue were frozen under irradiation of microwave at 2.45GHz. The measurements of supecooling degree and observation of morophology of frozen cell by using cryo-rnicroscopy were carried out.Summarizing these results, it was found that microwave have two aspects ; enhacing and releasing supercooling in dependence on microwave power. Especially, in the case of cooling by immersion in liquid nitrogen, the ice crystal size near the cooling surface decreased with increasing microwave power. Therefore, a combined use of microwave, irradiation and rapid cooling is considered to be a approach to reduce freezing injury. Regarding case of core region in the tissue, the effects of microwave on ice crystal size was diminished, since local cooling rate decreased due to heating effect caused by microwave increased. Thus, the size effects on microwave irradiation was found to be important factor to be considered.