Influence of dietary fibre on gluten proteins structure – a study on model flour with application of FT‐Raman spectroscopy

Dietary fibres are regarded as the source of polysaccharides and antioxidants such as polyphenols. However, addition of dietary fibre to bread causes significant reduction in its quality. The bread quality is connected with the structure of gluten proteins. For this reason, Fourier transform Raman spectroscopy was applied to determine changes in structure of gluten proteins modified by seven dietary fibres. The fibres were added to model flour reconstituted with wheat gluten and wheat starch. The model flour was used to provide gluten proteins of definite structure. The obtained results showed that six out of seven fibres caused similar changes in β ‐turn structures. The appearance of the band at 1642 cm −1 and the shift toward lower wavenumbers of the band at 1670 cm −1 in the difference spectra indicated hydrogen bonding of carbonyl groups in β ‐turns leading to protein folding/aggregation. Addition of fibre preparations caused also changes in conformation of disulfide bridges (S–S), corresponding to transformation to trans‐gauche‐gauche and trans‐gauche‐trans conformations at the expense of the stable gauche‐gauche‐gauche conformation. The S–S bonds in less stable conformations were formed inside the protein complex as well as between protein complexes in the form of β ‐structures. Generally, the observed changes in gluten proteins after addition of dietary fibres were results of interactions between fibre polysaccharides and gluten proteins rather than between polyphenols and gluten proteins. Copyright © 2015 John Wiley & Sons, Ltd.