Effect of Transglutaminase, Citrate Buffer, and Temperature on a Soft Wheat Flour Dough System

Transglutaminase (TGase) can improve the functional characteristics of proteins by introducing covalent bonds inter- or intrachains. Temperature and pH interfere with the protein structure and the catalytic activity of enzymes. Because these three factors can act synergistically, TGase, citrate buffer, and temperature were evaluated for their effects on the rheological and chemical changes in low-protein wheat flour dough. Dough strength, measured by microextension test, significantly increased with increasing levels of TGase (8 U/g of protein), with changes in pH of the citrate buffer (pH 6.5), and by the effect of interaction between these factors. The same trend was observed in the size-exclusion HPLC measurements, indicating that these two parameters have the effect of increasing gluten protein aggregation. Temperature had a significant effect on dough extension, measured by microextension test. The changes in secondary structure of gluten protein were investigated by FTIR second-derivative spectra (amide I region, 1,600-1,700 cm(-1)) and showed an increase in beta-sheet structures initiated by TGase, citrate buffer pH, and their interaction.