Effect of dietary fibre polysaccharides on structure and thermal properties of gluten proteins – A study on gluten dough with application of FT-Raman spectroscopy, TGA and DSC

The effect of four dietary fibre polysaccharides (microcrystalline cellulose (MCC), inulin (IN), apple pectin (AP) and citrus pectin (CP)) on structure and thermal properties of gluten proteins in the gluten dough was studied with application of FT-Raman spectroscopy, thermogravimetry (TGA) and differential scanning calorimetry (DSC). The commercially available wheat gluten was mixed with the polysaccharides in five concentrations: 3%, 6%, 9%, 12% and 18%. The obtained results showed that MCC, IN and small amount of pectin (3% and 6%) induced similar changes in the secondary structure of gluten proteins concerning formation of antiparallel-β-sheets connected by intermolecular hydrogen bonds from α-helices and β-sheets. Higher contents of pectin (9–18%) led to formation of aggregates and β-like aggregates. The observed changes in the secondary structure, conformation of disulphide bridges and environment of tyrosine and tryptophan of gluten proteins indicated partial dehydration of gluten network as a result of a competitive water binding by polysaccharides molecules (especially MCC and IN) during the dough mixing. TGA results also confirmed this statement. However, slightly different results were obtained for pectins. They not only competed for water with gluten proteins but also interacted with them since a thermogravimetric peak characteristic for pectin was observed in the derivative TGA profiles of gluten – pectin mixtures.