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

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。本研究对食品在冷冻过程中的热传递和损伤进行了分析和实验研究。在实验中，采用空气冲击法对金枪鱼肌肉组织进行降温。用低温扫描电子显微镜观察了组织的冷冻过程随温度的变化。对冻融组织解冻后的水滴和肌原纤维的Ca-ATPase活性进行了测定。总结这些结果，首先用降温速率阐明了结冰过程和肌纤维的脱水过程。其次，明确了肌纤维的脱水率是描述冷冻后食品品质变化的有效参数，胞外区的冷冻固形物含量是描述滴速的有效参数。第三，提出了肌肉组织的冷冻模型。通过分析，对组织中的温度分布、结冰状态、肌内外纤维的微观行为进行了数值计算。在这些结果的基础上，可以结合烹饪条件、膜透过率和组织大小来分析实现对冷冻后食品质量变化的准确预测。

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.