冻融对面筋蛋白结构及面粉粉质特性的影响

探讨冻融（以10 d作为一个冻融周期，在每个冻融周期的第5天，将冷冻在-18 ℃的样品升温至0 ℃，并在此温度下保持12 h后降温至-18 ℃继续冻融）对小麦面筋蛋白分子结构、自由氨基、自由巯基及粉质特性的影响.研究发现，随着冻融时间的延长，〖WTBX〗I〖WTBZ〗(0)值（散射角度为0时散射强度）呈现下降趋势，尤其是冻融前60 d，〖WTBX〗I〖WTBZ〗(0)由原样品的2.75105下降到1.75105，说明面筋蛋白的相对分子质量随着冻融时间的延长而降低.在冻融过程中自由氨基含量没有变化，而自由巯基含量上升，表明面筋蛋白相对分子质量下降的原因是由于二硫键断裂使得高聚物发生了解聚现象.添加冻融后面筋蛋白的粉质特性高于未添加的样品，而相对分子质量的下降对面粉粉质特性的影响表现在稳定时间和衰减时间上，而随着冻融时间延长其粉质特性呈现下降趋势，且与面筋蛋白的平均相对分子质量呈正相关.

Effects of Frozen Thaw Cyclic Storage on the Molecular Structure of#br# Hydrated Gluten and Farinograph Properties of the Dough

In this study, the effects of frozen thaw cycles (frozen at -18 ℃ with cycling to 0 ℃ for 12 h and then back to -18 ℃ per 10 days) on molecular structure, free amino groups content, free sulfhydryl groups and farinograph properties of gluten were studied by small angle X ray scattering (SAXS) and Micro dough LAB mixer. The results showed that during the frozen thaw cycles the I(0) of gluten proteins decreased with the increase in freeze thaw cycles, especially in the first 60 days storage, the value of I(0) (the scattered intensity implies at zero angle) decreased from 2.75105 for control to 1.75105 for the gluten stored for 60 days, which implies relative molecular mass dropping. The free amino group content changed only slightly, and the free sulphydryl group content increased, indicating that the depolymerisation of the gluten during freeze thaw cycling was due to the breakage of disulphide bonds. The farinograph properties of the dough added gluten which after the storage was higher than the one without gluten. The farinograph properties of dough deteriorated with added the frozen stored gluten, especially in the stability time and development time, which related to the relative molecular mass of the additive of the gluten. This suggests that the relative molecular mass and the molecular chain were the decisive factors influencing the quality of the dough for frozen storage.