Changes in the composition of the main polysaccharide groups of oil seed rape straw following steam explosion and saccharification

• Rape straw polysaccharides were analysed after pretreatment and after cellulolysis.
• FTIR mid-infrared spectra of samples was analysed using multivariate modelling.
• The proportion of glucose enzymatically released increased linearly with severity.
• Saccharification efficiency was associated with hemicellulose degradation.
• Pectins were disaggregated into pretreatment- and enzyme-labile groups.

The composition of oil seed rape straw treated by steam explosion with increasing severity was investigated before and after saccharification. Chemical changes were monitored by FTIR-ATR spectroscopy. Sugar contents were determined after acid hydrolysis. Discriminant analysis of the spectra before and after digestion showed the main compositional changes are losses of carbohydrates and a subsequent increase in the proportion of lignin. Construction of partial least squares (PLS) predictive models for the concentration of eight cell wall sugars indicated different fates for cellulose, hemicelluloses and pectic substances. No cellulose was lost during steam explosion and the amount digested to glucose increased linearly with severity. Pectin was partially degraded during steam explosion, but a bound fraction remained which was only released during saccharification. Hemicelluloses were gradually destroyed in the steam explosion process, and the extent of subsequent saccharification was most strongly associated with the breakdown of xylan-like hemicelluloses.