Mechanism of damages of polysaccharide gels and related foods caused by freezing-thawing cycle

用差示扫描量热法（DSC）和小角X射线散射法（SAXS）研究了可得然凝胶在冻融循环过程中的结构变化。从可得兰凝胶侵蚀水的量估计为32和40%，这取决于冷冻速率，分别为0.5 K/min和0.05 K/min。由三重螺旋和无规卷曲结构构成的网络结构在分子水平上没有急剧变化，但从SAXS轮廓中建议亚微米级的变化。采用差示扫描量热法（DSC）对冷冻-解冻和5 ℃保存对米饭的损伤进行了比较研究.与冻融处理相比，5 ℃贮藏导致的质构变化更大。这种变化是由于米饭中淀粉在5 ℃下老化所致。免疫组织化学染色，使用抗凝胶多糖兔抗体的淀粉-凝胶多糖混合物凝胶区分凝胶多糖结构域的淀粉域，因此可以澄清的局部变化凝胶多糖结构域的冻融循环。抗阿拉伯木聚糖兔抗体可用于竹笋细胞壁阿拉伯木聚糖凝胶的染色。这将使得能够通过冻融循环鉴定细胞壁中阿拉伯木聚糖凝胶的变化。

Structural changes in curdlan gel caused by a freezing-thawing cycle have been studied by differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS). The amount of eroded water from curdlan gel was estimated to be 32 and 40 %, depending on the freezing rate,for 0.5 K/min and 0.05 K/min, respectively. A network structure constructed by triple helical and random coil structures was not changed in a molecular level drastically, but a change in sub micrometer-order was suggested from SAXS profiles. Damages in cooked rice by a freezing- thawing cycle and keeping at 5 ℃ was comparatively studied using DSC. The keeping at 5 ℃ caused worse change in texture compared with the freezing-thawing treatment. The change is ascribed to the retrogradation of starch in cooked rice at 5 ℃. Immunohistochemical staining using an anti-curdlan rabbit antibody for starch-curdlan mixture gels discriminated the curdlan domains from the starch domains, and thus the local changes in curdlan domains by a freezing-thawing cycle could be clarified. Anti-arabinoxylan rabbit antibody was useful for staining arabinoxylan gel in cell wall of bamboo shoot. This will enable to identify the change the arabinoxylan gel in the cell wall by a freezing-thawing cycle.