Changes in Thermal Conduction and Mechanical Properties during Cooking Procedure of Foodstuffs due to Phase Trnsition

1)从上一个项目继续进行了一系列的实验研究，以描述加热过程中相变对食品力学性能和热传导的影响。2)尝试跟踪淀粉颗粒在水体系糊化过程中宏观和微观状态的变化，即光学显微镜观察、DSC测量和小应力下力学响应的观察。结果表明，马铃薯和小麦淀粉颗粒在糊化过程中的膨胀度明显高于糯米和糯米和玉米。DSC测试表明，马铃薯淀粉的表观转变热最高(-27.3MJ)，小麦淀粉的表观转变热最低(-15.2MJ)。在转变过程中，所有样品的力学响应，即瞬时弹性和稳定流动粘度，都可以用一类凸起曲线来表征，每个凸起曲线出现在70℃左右，对应于每个淀粉分子中晶区的消失。3)应用金属容器中加热平面沿x轴方向的温度上升曲线，测量了原料在加热过程中的相变对食品中热传递的影响。结果表明，在可可粉、绿茶纤维、小麦淀粉颗粒等样品中，随着可可粉、绿茶纤维、小麦淀粉颗粒等样品中热不敏感物质含量的增加，相变对升温曲线的扰动有减小的趋势.结果表明，在加热过程中，相变吸热分散在升温过程中，而升温速率的过程可能受到温度不敏感物质的存在的抑制.

1)A series of experimental studies have been continued from the last project so as to describe the effect of phase transition on the mechanical properties and thermal conduction in foodstuffs during heating procedures.2)An attempt was made to follow the changes in macro- and microscopic states of starch granule in water systems during gelatinization, i.e.optical microscopic examination, DSC measurement, and observation of mechanical responses under small stresses. The results obtained indicated that the potato and wheat starch granules show much higher degree of swelling in the course of gelatinization than those from glutinous and non-glutinous rices and corns. The DSC measurement, however, revealed that the apparent heat of transition was highest with potato starch (-27.3 mJ) among the samples to be tested, while that for wheat starch was lowest (-15.2 mJ). The mechanical responses, i.e. instantaneous elasticity and steady flow viscosity, of all the samples could be characterized by a types of convex curves during the process of transition, and each maximum appeared at around 70℃ corresponding to disappearance of the crystal region in each starch molecule.3)Measurements were made to clarify the effect of phase transition of ingredients on the heat transfer in foodstuffs during heating applied to the increasing curve of temperature along the x axis from heating plane in a metal vessel. It was found that the disturbance to the increasing curve of temperature due to phase transitions, e.g.melting fats or sol transition of hydrocolloids, tends to decrease with increasing amount of thermo-insensitive materials in the samples such as cocoa powder, fiber of green tea, wheat starch granule, etc. The results suggest that the endothermic heat of transition is scattered in the increasing temperature during heating, while the course of increasing rate of temperature may be restrained by the existence of thermo-insensitive materials.