Polysaccharides from grape berry cell walls. Part II. Structural characterization of the xyloglucan polysaccharides

Partially de-pectinated grape berry cell walls were sequentially treated with a xyloglucan-specific endoglucanase and with 4 M KOH. The endoglucanase-soluble xyloglucan oligosaccharides (XGO1) consisted predominantly of Glc, Xyl, Gal, and Fuc together with small amounts of Man, Ara and Rha residues that originated from contaminating mannan and pectin. The alkali-soluble xyloglucan (XGO-2) from exocarp and mesocarp was composed of Glc:Xyl:Gal:Fuc in a molar ratios of 4:1.7:1.8:0.4 and 4:1.5:2.5:0.5, respectively. XGO-1 and endoglucanase-treated XGO-2 were shown, by MALDI-TOF-MS for to contain oligosaccharides composed of XXXG-type building units: XXG, XXXG, XXLG or XLXG, XXFG and XLFG. These oligosaccharides were converted to their p-nitrobenzylhydroxyl derivatives and then separated and quantified by HPLC. XXXG, XXFG and XLFG were the quantitatively major oligosaccharides in mesocarp and exocarp cell wall xyloglucan. The distribution of XGO1, extracted with enzymes, is similar between exocarp and mesocarp, while XGO2 present an inversion of the amounts of XXFG and XLFG in skin and pulp.