Gluten-starch interactions in wheat gluten during carboxylic acid deamidation upon hydrothermal treatment.

After carboxylic acid deamidation upon heating (CADH), wheat gluten still contains a total of ∼10% insoluble fractions, of which ∼10% is starch, which depreciate the values of wheat gluten. To elucidate gluten-starch interactions and their role in the deamidation behavior of gluten, the macrostructural characteristics of gluten citric acid suspensions of different concentrations (1% and 10%, w/v) and with different types of residual starch chains (achieved by enzyme hydrolyzed by α-amylase and/or glucoamylase assisted by sonication) were investigated. We found the degradation of long starch chains and branched short chains induced dramatic bond-cleavages in insoluble glutenins and gliadins. FTIR and SDS-PAGE analyses indicated that without these two types of chains in the precipitates, the insoluble deamidated wheat gluten exhibited minimal changes in the molecular force and the conformation. Their glycosylation, hydrophobic force and hydrogen bonds between amylopectin and small proteins, such as LMW-GS and α, β, γ-gliadins, were detected. FTIR suggested that the associations between gliadins and amylopectin were covalent. Gluten-starch interactions were likely to cause an incomplete dissolution of wheat gluten during CADH. A simple model was proposed to clarify the aggregation state and the relationships between starch granules and wheat gluten components during CADH.