Mechanism of the ice crystal formation in the freezing of foods and cells and its relationship to the food processing and cell viability

在食品生产过程中，控制食品和活细胞中形成的冰结构对食品性质的预测和控制具有重要意义。研究了冰结构与冻结条件的关系，以及冰结构对冻结干燥、冻结浓度递进和冻结织构化行为的影响。从本项目获得的结果如下。(1)我们提出的三步冻结模型对温度相关冰段冻结和过冷相变行为的预测是有效的。(2)用方程对冻结锋的结构进行了理论和实验描述；（冻结锋移动速度）=（冻结锋处水的传质速率）x（冻结锋表面积）。(3)在冷冻干燥过程中，由于形成了细小的冰结构，冷冻速度越快，干燥速度越慢。在混悬液和溶液的递进冻结浓度中，冻结速度越快，冻结锋结构越复杂，冻结浓度产率越低。为了提高冷冻浓缩收率，搅拌对冷冻锋传质速率的提高是有效的。在大豆蛋白的冷冻软化过程中，冷冻速度越慢，蛋白质变性程度越高。所有这些结果都可以用(2)中冻结锋结构与冻结速度之间的理论关系来解释。(4)酵母和Bailey Alicante A培养细胞的冷冻伴随着相当程度的过冷。作为冷冻保护剂，DMSO具有降低冰点和增加不冻水含量两种不同的作用。

Control of the ice structure formed in foods and living cells is very important for the prediction and the control of food properties in the food manufacturing process. Relationship between the ice structure and the conditions at the freezing was investigated along with the effects of the ice structure formed on the behaviors in the freeze drying, the progressive freeze concentration, and the freeze texutization. The results obtained from the present project were as follows.(1)The three step freezing model proposed by us was effective for the prediction of the phase change behavior involving the freezing of the temperature dependent ice fraction and the supercooling.(2)The structure of the freezing front was described theoretically and experimentally by the equation ; (moving speed of the freezing front)=(mass transfer rate of the water at the freezing frotit)x(surface area of the freezing front).(3)In the freeze dryinic, the faster freezing speed gave the slower drying rate because of the fine ice structure formed. In the progressive freeze concentration of suspension and solution, the faster freezing speed gave the poorer freeze concentration yield through the complex structure of the freezing front. For the improvement in the freeze concentration yield, increase in the mass transfer rate at the freezing front by agitation was erective. In the freeze texurization of soy protein, the slower freezing gave the higher extent of the protein denaturation. All of these results were generally explained by the theoretical relationship between the freezing front structure and the freezing speed described in(2).(4)Freezing of yeast and the culture cell of Bailey Alicante A was accompanied with a substantial extent of supercooling. As a cryoprotectant, DMSO had two different fucnctions : the freezing point depression and the increase in the unfreezable water content.