Incorporation of soy proteins into the wheat–gluten matrix during dough mixing

Farinograph methodology was used to evaluate the possible incorporation of soy proteins into a glutenin–soy complex during mixing and to study the contribution of soy proteins to the chemical and physical properties of the dough. To facilitate the interaction of soy and wheat proteins, a redox process was used, which allowed the partial reduction (using dithiothreitol, DTT) and subsequent reoxidation (using potassium iodate) of glutenin without changing its functionality in the dough (a composite of equal parts of wheat and soy flours, 300 g in total). Either raw soy flour (RSF) or physically modified soy flour (PMSF) was used as the soy component. Dough samples were taken at peak mixing time and at break time during mixing, and these were freeze dried for SE-HPLC analysis and capillary electrophoresis (Lab-on-a-chip).SE-HPLC results showed that soy globulins interact with gluten proteins in the composite dough, forming aggregates of high molecular weight. Partial reduction and oxidation of these doughs at peak mixing time resulted in higher SE-HPLC polymeric protein profiles (HMW) compared to those of control composite doughs, based on extraction and SE-HPLC analyses. Unextractable polymeric protein (UPP%) increased from 21% to 27% (15–25% at break time) as a result of the reduction–reoxidation treatment for the PMSF–wheat doughs. In contrast, %UPP values were much lower for the doughs made from raw soy–wheat flours, with %UPP increasing from 6% to 9% (3–6% at break time) as a result of the reduction–reoxidation treatment. Capillary electrophoresis (Lab-on-a-chip) further revealed that the reduction–reoxidation treatment had facilitated the interaction of glutenin subunits and soy proteins (11S subunits), probably through the oxidation of SH groups.