Hierachical Study on Heat Transfer and Damage of Food during Freezing Process

冷冻可以减缓或停止一些生物反应，以保存食物。冷冻对保持食物的味道是致命的，这也是事实。在冷冻过程中，细胞内外的结冰、渗透水透过细胞膜、细胞变形等行为都发生在微观尺度上，它们会对食品造成严重的损伤，这些损伤与蛋白质的滴落和变性有关。实验中采用鼓风法对金枪鱼肌肉组织进行冷却。用冷冻扫描电镜观察了组织的冷冻过程与温度的关系。通过对冷冻组织解冻后滴水量和肌原纤维Ca-ATP酶活性的测定，初步阐明了结冰和肌纤维脱水过程与降温速率的关系。其次，明确了肌纤维的脱水率是描述食品冷冻后品质变化的有效参数，胞外区的冻固分数是描述滴水率的有效参数。第三，建立了肌肉组织的冻结模型。通过分析，数值计算了组织内的温度分布、结冰状态、肌内肌纤维和肌外肌纤维的微观行为。在此基础上，结合冷冻条件、膜透性和组织尺寸，可以准确地预测食品冷冻后的品质变化。

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 intracellular 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.In this research project, heat transfer and damage of food during freezing process have been studied analytically and experimentally. In experiments, muscle tissue of tuna was cooled by airblast method. The freezing process of tissue was observed by using a cryo-scanning electron microscope as a function of temperature. The drip after thawing of frozen tissue and Ca-ATPase activity of the myofibril were also measured.Summarizing these results, firstly, the process of ice formation and the dehydration of muscle fiber were clarified with cooling rate. Secondly, it is made clear that the dehydration ration of the muscle fiber is available parameter which described changing in quality of food after freezing, and the frozen solid fraction in extracellular region is the useful parameter to described the rate of drip. Thirdly, the freezing model of muscle tissue was proposed. Through analysis, the temperature distribution in the tissue, the state of ice formation, the microbehavior of intra- and extra-muscle fiber are numerically calculated. On the basis of these results, the accurate prediction of changing in quality of food after freezing can be achieved analytically in conjunction with cooing condition, membrane permeabily, and tissue size.