Improved functional properties for soy-wheat doughs due to modification of the size distribution of polymeric proteins

Physical modification of soy flour was shown to greatly improve the dough and baking qualities of soyââ"šÂ¬Ã¢â‚¬Å“wheat (1:1) composite doughs, compared to raw soy flour, giving better stability and Rmax, although extensibility was still below that of the wheat dough. Reasons for improvements caused by the physical-modification process were sought by determining the relative size distribution of proteins in the soyââ"šÂ¬Ã¢â‚¬Å“wheat composite doughs by size-exclusion high-performance liquid chromatography (SE-HPLC). Results were expressed as the proportion of ââ"šÂ¬Ã‹Å“unextractable polymeric proteinââ"šÂ¬Ã¢"žÂ¢ (%UPP)ââ"šÂ¬Ã¢â‚¬Âthe proportion of the protein that is over 100,000 Da and only extractable after sonication. Protein extracts from the soyââ"šÂ¬Ã¢â‚¬Å“wheat dough were sampled at different stages of dough mixing and fermentation, and their molecular-size distributions evaluated. Unextractable soy proteins were lower in raw soy flour (only 8% UPP) than in two physically-modified soy flours (19 and 34% UPP, respectively). Unextractable polymeric protein was much greater for wheat flour (57% UPP). After mixing a 1:1 soyââ"šÂ¬Ã¢â‚¬Å“wheat composite dough, the %UPP was 36 and 22 (for the two types) when made from physically modified soy flours, compared to 8 for a composite dough using raw soy flour, and 43 for a wheat-only dough. The higher proportion of UPP for the wheat-modified soy doughs was taken as a reason for this composite dough providing better dough and baking qualities. Prolonged fermentation time caused a decrease in UPP percentages for all composite doughs and for the wheat-only dough.