Study on the interactions between soy and semolina proteins during pasta making

Spaghetti produced in a pilot plant were made from semolina and semolina blended with 10%, 15%, 25% or 50% of defatted soy flour (DSF) or toasted soy flour (TSF).Proteins of spaghetti were characterized by size exclusion-high-performance liquid chromatography (SE-HPLC). Results showed that soy globulins interact with semolina proteins during pasta making, forming polymers of high molecular weight. Of these, the sodium dodecyl sulphate-unextractable components were significantly higher (p < 0.001) (up to 49% unextractable polymeric proteins) (UPP) than that of spaghetti made of semolina (24.6% UPP). The decrease of S–S bonds and the increase of –SH free groups in the DSF–semolina spaghetti, with respect to that made of only semolina, suggest that polymerization among the different classes of proteins involves interaction by sulphydryl residues in blends with above 15% of DSF and that soy proteins tend to disrupt own gluten S–S interchange system. In the TSF–semolina spaghetti the increase of S–S bonds was higher with respect to that of –SH free, suggesting that the heat treatment, to which the TSF proteins were subjected, allowed them to cross link to semolina proteins by disulphide bonds.