Revisiting the contribution of ATR-FTIR spectroscopy to characterize plant cell wall polysaccharides

The contribution of ATR-FTIR spectroscopy to study cell wall polysaccharides (CWPs) was carefully investigated. The region 1800-800 cm^-1 was exploited using principal component analysis and hierarchical clustering on a large range of different powders of CWPs based on their precise chemical characterization. Relevant wavenumbers were highlighted for each CWP: 1035 cm^-1 was attributed to xylose-containing hemicelluloses, 1065 and 807 cm^-1 to mannose-containing hemicelluloses, 988 cm^-1 to cellulose, 1740 and 1600 cm^-1 to homogalacturonans according to the degree of methylation. Some band positions were affected by macromolecular arrangements (especially hemicellulose-cellulose interactions). However, as arabinan and galactan did not reveal distinctive absorption bands, ATR-FTIR spectroscopy did not allow the discrimination of cell walls differing by the abundance of these polysaccharides, e.g., those extracted from apple and beet. Therefore, the application of ATR-FTIR could remain sometimes limited due to the complexity of overlapping spectra bands and vibrational coupling from the large diversity of CWP chemical bonds.