Gelation properties of deamidated soluble wheat proteins

Compared with native wheat gluten proteins, chemically modified deamidated gluten proteins are more readily dispersed in aqueous solution. lit this paper the gelation behaviour of commercial deamidated gluten, commonly referred to as soluble wheat protein (SWP) on heating as well as its interaction with calcium and basic proteins was investigated. Soluble wheat protein decreased in viscosity on heating at 60 degrees C due to the breakdown of protein aggregates which was observed by phase contrast microscopy. Heating to 60 degrees C was accompanied by an increase in hydrophobicity without conformational transitions as observed by differential scanning calorimetry. In aqueous solutions at concentrations greater than 17% w/w and after autoclaving at 120 degrees C, SWP produced firm gels which were examined by large deformation testing. In the presence of calcium strong but coarse gels were formed which exhibited syneresis. The addition of 0.1-0.5% w/w of basic lysozyme or clupeine to the highly negatively charged SWP induced gelation at the lower temperature of 80 degrees C which was detected by small deformation rheological testing and microscopy using basic and acidic stains. The structure and mechanism of lysozyme-induced gelation of SWP is different from the high thermal (>100 degrees C) gelation of SWP alone. In the lysozyme-induced gelation non-covalent mainly electrostatic interactions occur between the positively charged lysozyme and the negatively charged soluble wheat proteins with the absence of conformational changes in the SWP. In contrast, in the heat gelation of SWP proteins at 120 degrees C it is proposed that the intra-disulphide bonds are broken leading to conformational changes and subsequent association and gelation. This mechanism is supported by the fact that gelation occurred spontaneously in the presence of urea and beta-mercaptoethanol indicating that in SWP the disulphide bonds normally prevent gelation unless exposed to very high heat (120 degrees C) or disulphide reducing reagents.