Rheological properties of xyloglucans from different plant species

The rheological properties of three xyloglucans (XGs) from the extracellular medium of suspension cultured Nicotiana plumbaginifolia cells, apple pomace and tamarind seeds, with different structural features and molecular weights have been studied. The molecular weight (weight average) of the Nicotiana, apple pomace and tamarind seed XGs determined by multi-angle laser light scattering were 129, 219 and 833 kDa, respectively. Tamarind seed XG had the highest viscosity and Nicotiana XG had the lowest viscosity, with that of apple pomace XG intermediate. The viscosity of apple pomace XG at 5% w/v was almost equivalent to that of tamarind seed XG at 2% w/v, but their behaviour at high shear rates differed; both XGs were non-Newtonian in their rheological properties, but that from tamarind seeds showed more pronounced shear-thinning. The viscosity of Nicotiana XG at 5% w/v was almost equivalent to tamarind seed XG at 0.5% w/v, displaying Newtonian behaviour. Modification of the molecular weight of the XGs and their degree of branching revealed that differences in viscosity between the molecules, and their shear-field behaviour, was due primarily to differences in molecular weight. Removal of fucose residues from apple pomace XG decreased the viscosity of solutions from 8 to 4 mPa·s, whereas removal of both fucose and galactose from apple pomace XG, resulted in precipitation from solution. Deacetylation of Nicotiana XG also resulted in precipitation from solution.