Physicochemical characterization of xylan-type hemicellulose from corn cobs
Xylan, Gel Permeation Chromatography, corn cobs, Hemicellulose.
The rheological properties of xylan extracted from corn cobs and the influence of such characteristics on the application of this polymer in the pharmaceutical field were previously described by our research group. However, the complete physicochemical characterization was not reported. The aim of the present work was to characterize the xylan-type hemicellulose by using different analytical techniques. The Gas Chromatography with Flame Ionization Detector (GC-FID) analysis showed that our xylan-type hemicellulose is basically composed of xylose (64.65%), arabinose (12.64%) and glucose (11.04%). A few amounts of Rhamnose, galactose and mannose were also detected. The arabinose/xylose ratio was 0.19, showing a low branching of xylan chains by arabinosyl residues, and consequently poor solubility in water. Xylan presented a backbone composed by β-(1→ 4)-linked DXylopyranose and a molecular weight of 31,300 g/mol with a polydispersity of 1.06. In addition, the 1H and 13C NMR revealed a weak peak at δ 5.3 ppm characteristic of 4-O-methylglicuronic acid and no peak related to acetyl groups, confirming the deacetylation of xylan during alkaline extraction. Moreover, the xylan powder XRD highlighted the semicrystalline state, characteristic of deacetylated xylan. Thermal analysis showed a good thermal stability of the polymer (186 °C). According to the results, the polymer characterized is a deacetylated heteroxylan, insoluble in water, with good thermal stability