The application of DFRC method for the analysis of carbohydrates in a peat bog: Validation and comparison with conventional chemical and thermochemical degradation techniques

摘要

Traditional acid hydrolysis is the main method used for carbohydrates characterization in soils and sediments. It has been used to cleave the glycosidic bond, yielding monomers that compose polysaccharides of the noncellulosic pool (free, ligno-cellulosic and hemicellulosic carbohydrates). In this study, the widely used chemical and thermochemical degradation procedures have been compared with the derivatisation followed by reductive cleavage (DFRC) method. This method presented efficiency in specifically cleaving the aryl ether bonds, yielding for sugar moieties linked to aromatic structures (ligno-cellulosic fraction). Once applied for peat samples, some discrepancies were observed. DFRC method revealed some information about the origin of carbohydrates that was hidden from the traditional chemical and thermochemical degradation methods. Several patterns of carbohydrates have been obtained with DFRC indicating difference in the origin and/or degradation rates between monosaccharides. For xylose, it showed an increase in the catotelm (deepest layer of the peatland), indicating an angiosperm vegetation input at the early stage of the peatland formation. Ribose, commonly known as a microbial indicator, showed the same profile as for hexoses and deoxyhexoses, with acid hydrolysis. The difference in the profile yielded in the case of DFRC method, revealed its microbial input. These information were hindered from acid hydrolysis and thermochemolysis, as the first showed nearly the same profile for all monosaccharides and the second one didn't have the capacity to analyze arabinose and ribose. Generally, higher similarity was obtained between DFRC and acid hydrolysis than between DFRC and thermochemolysis. This is due to the difference of mechanisms involved in chemolytic and thermochemolytic methods. For the first group, both methods shared acid conditions and milder temperature conditions if compared to the second group. In addition thermochemolysis is performed under