**3.1 Xylan extraction**

Chestnut wood glucuronoxylans were extracted by this procedure (**Figure 2**). They were obtained from chlorite-delignified sawdust by aqueous KOH extraction. The MGX has been extracted with a yield of 19%. The obtained fraction is characteristic of a classical MGX with more than 99% of xylose and 4-*O*-methylglucuronic acid (typical markers of glucuronoxylans). 4-*O*-methylglucuronic acid contents were 16.6% (molar ratio), which is in agreement with the data obtained by the colorimetric assays (17.4, mass ratio) and the

Xyl/4-*O*-MeGlcA ratio was found: 6.1. However, concerning the size of the extracted molecules, a DP of about 200 was found which is a typical result for this kind of products. This MGX is represented in **Figure 3**.
