Effects Of Hydrocolloids On Protein Structure Of Gluten During Freeze-thaw Cycles Storage

In this paper, wheat gluten and three kinds of hydrocolloids(CMC, Xanthan Gums, Carrageenan)were used as model materials, The basic data of macroscopic and microscopic research were used to analyze the effects of freeze-thaw cycles(frozen at-18 ? with cycling to 0 ? for 12 h and then back to-18 ? per 10 days) on rheological properties, molecular weight and distribution, fractal dimension and microscopic property of gluten with hydrocolloids and explore the effect of hydrocolloids on frozen stability of gluten, which has great commercial benefits as it will provide a theoretical guideline to accelerate the application of hydrocolloids in frozen dough. The main results are as follows:(1) The effect of hydrocolloids on the storage modulus(G'), loss modulus(G'') of gluten were studied by rheometer. The result showd that during the freeze-thaw cycles, the storage modulus(G'), loss modulus(G'') of the contral was significantly decreased, the addition of hydrocolloids can abate the decrease trend of the storage modulus(G') and loss modulus(G''). The hydrocolloids can protect the gluten network structure, The effect of three kinds of hydrocolloids was as follows: carrageenan, xanthan gum, CMC.(2)Impact of hydrocolloids on molecular weight and distribution of gluten during freeze-thaw cycles storage. The effects of hydrocolloids on molecular weight and distribution, protein subunits, free sulfhydryl group and fractal dimension were studied by the multiangle laser light scattering(MALLS) in combination with size exclusion chromatography(SEC), small angle X-ray scattering(SAXS). The results showed that the addition of CMC can inhibit the rapture of disulfide bonds, reduce the depolymerisation caused by recrystallization and alleviate the trend of the decreasing of fractal dimension during the freeze-thaw cycles. The small molecular proteins of the gluten added xanthan were assembled, and the molecular weight was increased. While the molecular weight of the gluten added carrageenan descreased slightly contrast with the control. The SDS-PAGE profiles revealed that there were no remarkable difference and relative mobilities of band for the gluten protein subunits. The free sulphydryl group content increased during the storage, the 4.89 ?mol/g for control compared with 4.13 ?mol/g for the gluten added carrageenan stored for 120 days, which implying the carrageenan can offer protection to the disulfide bonds. These results indicate that the addition of hydrocolloids could reduce the depolymerisation caused by recrystallization and protect the structure of gluten.(3)Impact of hydrocolloids on microscopic property of gluten during freeze-thaw cycles storage. The changes in protein secondary structure of gluten were investigated by fourier transform infrared spectrometer(FTIR). The analysis showed a decrease of the amount of ?-helixes and random coil was found accompanied by an increase of the content of the extended ?-sheet conformations. And the addition of hydrocolloids could effectively inhibit the transformation of the secondary structure. SEM photographs showed that the network was weakened with increasing freeze-thaw cycles storage time, the pore size of the control sample was increased to 50 ?m after stored for 120 days, while the gluten added CMC and carrageenan were highly uniform in size. Hydrocolloids had strong water absorbability, and dispersed in gluten to reduce the growth of ice crystals, and reduce the damage of gluten network structure, in order to protect the ultrastructure of gluten protein. CLSM photographs showed that the distribution of hydrocolloids in the gluten structure were changed.(4) Impact of hydrocolloids on baking quality during freeze-thaw cycles storage. The result showed that, the capacity of gas production of control group were greatly reduced, network structure was destroyed, hardness of bread was significantly increased. With addition of CMC and carrageenan could protected frozen dough, while the hardness was increases adding with Xanthan gum. In conclusion, CMC and carrageenan can be used as good conditioners to frozen dough production.