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

采用差示扫描量热法（DSC）和小角x射线散射（SAXS）研究了冻融循环对凝乳凝胶结构的影响。在0.5 K/min和0.05 K/min的冻结速率下，凝乳凝胶的侵蚀水量估计分别为32%和40%。由三螺旋结构和随机线圈结构组成的网络结构在分子水平上没有发生明显的变化，但从SAXS谱中可以看出亚微米级的变化。用DSC法比较研究了5℃冻融循环和5℃保温对熟米的危害。与冻融处理相比，5℃的保温处理导致织构的变化更大。这种变化是由于淀粉在5℃下的退化。用抗凝乳蛋白兔抗体对淀粉-凝乳蛋白混合凝胶进行免疫组化染色，将凝乳蛋白结构域与淀粉结构域区分开来，从而阐明在冻融循环过程中凝乳蛋白结构域的局部变化。兔抗阿拉伯木聚糖抗体可用于竹笋细胞壁阿拉伯木聚糖凝胶的染色。这将有助于通过冻融循环确定阿拉伯木聚糖凝胶在细胞壁中的变化。

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.