| Wheat gluten is a byproduct of the wheat starch industry. The water-solubility of it is strongly limited so that its applications are very narrow in the food-processing. Hydrochloric acid was one of the most effective acid catalyst used frequently for protein deamidation. The disadvantages of deamidation on proteins with it, such as the uncontrollable hydrolysis degree, the production of potentially carcinogenic compounds, and the isomerization of certain amino acids in proteins, have yet to be solved. The aim of the present study was to modify wheat gluten by carboxylic acid deamidation upon hydrothermal treatment. The degree of hydrolysis, functional and conformational properties of deamidated wheat gluten (DWG) were evaluated. Optimal conditions and some intrinsic mechanisms of deamidation on wheat gluten with organic acids upon hydrothermal treatment were studied. Protective effect of DWG after dialysis subjected to ultrasound treatment was also investigated. Moreover, susceptibility of wheat gluten to enzymatic hydrolysis following deamidation and sensory characteristics of the resultant hydrolysates, in together with the applications of DWG on yoghourt and drug controlled delivery system were evaluated.Three carboxylic acids (acetic acid, succinic acid and citric acid) were used to deamidate wheat gluten with reference samples investigated of wheat gluten treated with HCl. Deamidation conditions were optimized. Changes in deamidation degree, hydrolysis degree, nitrogen soluble index, the foaming and emulsification properties, the tertiary and secondary conformation and nutritional property of wheat gluten deamidated with carboxylic acids were identified. Carboxylic acids were found to effectively deamidate the amides in wheat gluten proteins into carboxyl groups, which resulted in a significant increase of the nitrogen soluble index of wheat gluten. Deamidation of wheat gluten by carboxylic acids was found to be more efficient than that with HCl and significantly improved functional properties of wheat gluten. Wheat gluten deamidated with carboxylic acid exhibited improved flexible protein molecules, favorable changes in the tertiary and secondary structures and better nutritional characteristics. The solubility of wheat gluten after carboxylic acid deamidation increased in the isoelectric region of untreated wheat gluten (around pH 6.0). The isoelectricpoint of these proteins was shifted to a basic pH and existed in a broad pH regions. Changes of aggregation behavior of wheat gluten during carboxylic acid deamidation upon hydrothermal treatment were investigated to test the influences of deamidation on the aggregation extent of wheat gluten. Hydrothermal treatment induced that the size of soluble wheat gluten aggregate progressively increased due to the cross-linking of gliadins and slowly cleaved glutenins. But significant changes in molecular weight distribution, solubility under six denaturing agents'treatment and Zeta potential of wheat gluten aggregates were observed at 6 min heating time and distinct shift of intra-/inter-molecular interactions of wheat gluten aggregates occurred before and after 6 min heating treatment respectively. Moreover, as heating time increased, the island-like aggregates decreased markedly and the striped aggregates increased notably. To explain the aggregation behavior in this case, we postulated that the extent of aggregation of wheat gluten depended on the balance between intra-/inter-molecular electrostatic repulsion, the non-covalent and disulfide bonds formation in the system. Hence, a scheme was drawn, which appeared to be the mechanism responsible for the aggregation of wheat gluten through thermal cross-linking and opening up of the network structure of wheat gluten aggregates by deamidation.The reasons for the decreasing of solubility of DWG during dialysis were investigated. Results from DLS, SDS-PAGE, FTIR, morphology and molecular forces change of DWG during dialysis showed the increasing of hydrogen bonds due to the decreasing of protein surface potential increased the interaction of proteins. The effect of sonication factors, including sonication power percentage, process time and temperature, on the soluble nitrogen index (NSI) of succinic acid deamidated wheat gluten (SDWG) after dialysis was investigated. On base of the results of univariate factor analysis upon sonication, response surface analysis was used to optimize the process condition according to the response of NSI of SDWG. The optimal condition of sonication power percentage, treating time and sonication temperature obtained was 100 W, 10 min and 44℃, respectively, where the NSI of sample treated reached 77.28%. Changes of functional properties of the protein in SDWG upon sonication were determined. The percentages of enhancement in the foaming capacity and stability of sample after sonication were 11% and 20%, respectively. And a similar trend of significant growth in emulsifying properties of samples was also observed.Investigation on applications of DWG on yoghourt and controlled delivery system showed that the ferment time of yoghourt decreased after the addition of DWG, and it was with a good textile and sensory evaluation at the DWG addition percentage of 3% for total casein amount. For the application in the field of fish oil (FO) controlled delivery system, the most efficient condition was obtained at 50.4 mg/ml for SDWG and 3:3 (w/w) for FO/SDWG ratio, with an EE of 81.8%. In this condition, confocal microscopy showed FO well encapsulated in SDWG microspheres. SEM showed sunken pores and fractures inside microspheres after FO was extracted, confirming the presence of FO in microspheres. FTIR and electrophoresis showed during microspheres formation dramatically elevated SWDG aggregation resulted in intermolecular-crosslinking and enhanced interactions (hydrogen bonds and hydrophobic interactions) between SDWG and FO. In the evaluations of in vitro experiments in simulated gastric fluid and oxidation stability during storage, results indicated that SDWG matrix protected it from both oxygen and gastric fluid, resulting in improved storage stability and release property.
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