Structural heterogeneity of wheat arabinoxylans revealed by Raman spectroscopy

A set of arabinoxylan samples differing in their arabinose composition and various samples of arabino-xylo-oligosaccharide samples were analysed by Raman spectroscopy. Specific signatures for arabinose substitution were found in several spectral regions, that is, 400–600, 800–950 and 1030–1100 cm−1. A linear relationship was observed between the peak ratio 855/895 cm−1 of the second derivative spectra and the A/X ratio determined by chemical analysis. Moreover, spectral changes were observed in the 400–600 cm−1 region assigned to the coupled vibrations mode in the skeleton: while the intensity of the band at 570 cm−1 increased with the degree of substitution, that at 494 cm−1 decreased. Similarly, a linear relationship was observed between the peak intensity ratio 570/494 cm−1 calculated on the second derivative spectra and the composition data. Analysis of Raman spectra of arabino-xylo-oligosaccharides allowed to identify specific spectral features of disubstitution.