Study On Wheat Gluten And Starch Composites

Biodegradable materials based on wheat proteins have received more and more attention in recent years. Wheat has a huge gross output in China and its industrial products such as gluten and starch are comparable in price in comparison with other chemical materials. Preparing biodegradatable composites based on wheat gluten and starch, as alternatives to traditional materials, will be helpful to deal with the problems of pollution and resources.The main objectives of this thesis are to prepare wheat gluten/starch composites and to investigate the effects of starch content, molding temperature, glycerol content, relative humidity and starch modification on mechanical properties, and moisture absorption and dynamic rheological behavior of the composites. The results showed that the optimized water content decreased with increasing starch content while loss and storage moduli increased markedly. The doughs exhibited a gle-like behavior with appearance of secondary plateau in the low frequency region due to the complicated physical interactions between starch and gluten. With the increment of the starch content and the forming of physical network, the relaxation of protein chains was depressed. In the composites molded below 110℃, starch underwent gelification during heating the composites, which promoted the crosslinking reaction of protein chains.The molding temperature and glycerol content significantly influenced the mechanical properties of the gluten/starch composites. Increasing molding temperature could improve Young's modulus and tensile strength and decrease strain at break due to an increase in crosslinking density. At constant glycerol content, addition of starch with a starch content above 14% could improve modulus while tensile strength and strain at break decreased with increasing starch content. Addition of glycerol as a plasticizer weakened molecular interaction between starch and gluten, which led to decreases in Young's modulus and tensile strength. At the same time, strain at break increased with increasing glycerol content due to an improvement in chain mobility.Dialdehyde starch was prepared by oxidating virgin starch and the dialdehyde starch was used to crosslink gluten proteins. Tensile strength of the dialdehyde starch filled gluten composites was improved remarkably in comparison with the virgin starch. The composite showed optimized mechanical properties at a gluten/dialdehyde starch ratio of 19/1 (w/w). Moisture absorption of the composites was highly dependent on relative humidity and glycerol content. The nature of starch did not influence moisture absorption significantly.