Impact Of Xanthan Gums On The Frozen Stability Of Gluten Proteins

Due to the growth and migration of ice crystals in the process of freezing storage, the gluten network structure of the wheat dough was deteriated, leading to the degradation of the frozen dough products. In this dissertation, wheat gluten was used as model materials, and gluten-water-xanthan system was built, the effect of xanthan on the frozen storage stability of gluten was elucidated by exploring the different addition ratio of xanthan gum and frozen storage time on the rheological characteristics, molecular weight size and distribution, hydrophobicity, aggregated structure and thermodynamic behavior of wheat gluten. Use those basic data of macroscopic and microscopic research to explore the relationship between the xanthan content and gluten structure and properties changes during frozen storage, which has great commercial benefits as it will provide a useful practical guideline to accelerate the application of xanthan in frozen dough.The main research and results are as follows:(1) The storage modulus(G’), loss modulus(G’’) and loss tangent(tan δ= G"/G’) of wheat gluten with different amount of xanthan addition at different frozen storage time were studied by using the rotational rheometer. The results show that with the extension of freezing storage time, G’、G’’ and tan δ of the gluten was reduced, and the addition of xanthan can abate the decrease trend of G’、G’’ and tan δ of the gluten, which showed that in the process of freezing storage, the gluten network structure of the wheat dough was damaged, and the xanthan can protect the gluten network structure.(2) Wheat gluten and its subunits were affects by different frozen storage time and different amount of xanthan added on molecular weight size, distribution analyzed by SEC-MALL and SDS-PAGE. The SEC-MALL result indicated that the gluten protein molecular weight increased gradually with the extension of freezing storage time, from the original 1432 k Da rose to 4139 k Da. And the increasing trends of the frozen gluten protein molecular weight were weakened due to the addition of xanthan. It was clearly seen that no remarkable difference and relative mobilities of band could be observed for wheat gluten subunits with or without xanthan in the frozen storage process. The free sulfhydryl group content of the gluten increased with the frozen storage time, indicating that the depolymerization of gluten during frozen storage was attributed to the breakage of disulfide bond, and xanthan can protect disulfide bond from destroying.(3) Hydrophobicity of wheat gluten surface was falling with the extension of freezing storage time, the original gluten hydrophobic index dropped from 1235.5 to 1098.5 when frozen storage for 20 days. And the additions of xanthan can significantly affect the hydrophobicity of wheat gluten. The particle size of wheat gluten was increased with the frozen storage time extend, but was first decreased and then increased with xanthan.(4) Microstructure, secondary structure and thermal properties of wheat gluten were analyzed by SEM, FTIR and TGA, the results indicated that the gluten structure was damaged with the process of the frozen storage, and the addition of xanthan can improve the structure stability of wheat gluten.