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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 À1 and the shift toward lower wavenumbers of the band at 1670 cm À1 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-gauchegauche 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.

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Alizarin is one of the dyes extensively investigated as an example of a molecule capable of serving as a light absorber and an electron donor in model systems designed for the new type solar cells. Using the Stark effect measurements for alizarin, both free in solution and adsorbed to TiO2 nanoparticles, the question has been addressed whether the excited-state orbital of adsorbed alizarin extends into the solid and involves the orbitals of the Ti atom or remains localized within the alizarin molecule. Because an important role can be played by the electric field at the charged surface of the nanoparticles, the field was modulated by changing the pH of the medium. The results reveal a substantial dipole moment change on the electronic excitation of the alizarin−TiO2 system, |Δμ| ≈ 10 Debye units or slightly more. The observed dependence of the absorption maximum and the measured |Δμ| on pH were used to distinguish between Δμ directed toward the nanoparticle surface and that corresponding to the intrinsic rearrangement of electrons within alizarin or, in reverse direction, corresponding to more- or less-complete electron transfer from alizarin onto the orbitals of Ti and adjacent atoms comprising a localized surface (or a delocalized conductive) state. The results qualitatively contradict a significant dye-to-solid charge-transfer character of the electronic transition. It is shown that they can be interpreted in a self-consistent way by considering, in a first approximation, the light absorption by alizarin monoanion subject to the electric field generated by the charged nanoparticle surface.