Fractionation of xyloglucan fragments and their interaction with cellulose.

Tamarind seed xyloglucan was partially degraded with a purified endoglucanase (endoV) from Trichoderma viride. Analysis by high-performance anion-exchange chromatography showed that this digest was composed of fragments consisting of 1 to 10 repeating oligosaccharide units ([xg]1-[xg]10). To study the adsorption of xyloglucan fragments to cellulose in detail, this digest was fractionated on BioGel P-6. Fragments were separated satisfactorily up to 5 repeating oligosaccharide units ([xg]5). The galactose substitution of the fragments increased with increasing molecular weight. The BioGel P-6 pools, as well as polymeric xyloglucan ([xg] infinity), were tested for their ability to interact with Avicel crystalline cellulose. Quantitative binding to cellulose occurred for sequences consisting of (at least) 4 repeating units. The adsorption of [xg]4 to Avicel was very high relative to that of [xg] infinity. The dimensions of these fragments were such that they could also penetrate the smaller pores of cellulose. Apparently, the effective surface area for the polymers is much smaller. Adsorption isotherms of [xg] infinity and [xg]4 showed a pattern that is typical for polydisperse systems. However, the mechanisms underlying these patterns were different. At high xyloglucan concentrations, this polydispersity resulted in preferential adsorption of the larger molecules in the case of [xg] infinity and a more extensive colonization of the smaller pores of cellulose in the case of [xg]4. The pH influenced the interaction between xyloglucan (fragments) and cellulose to only a small extent.