RHEOLOGICAL PROPERTIES OF XYLOGLUCANS FROM DIFFERENT PLANT-SPECIES

The rheological properties of three xyloglucans (XGs) from the extrace llular medium of suspension cultured Nicotiana plumbaginifolia cells, apple pomace and tamarind seeds, with different structural features an d molecular weights have been studied. The molecular weights (weight a verage) of the Nicotiana, apple pomace and tamarind seed XGs determine d by multi-angle laser light scattering were 129, 219 and 833 kDa, res pectively. 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 th at of tamarind seed XG at 2% w/v, but their behaviour at high shear ra tes differed; both XGs were non-Newtonian in their rheological propert ies, but that from tamarind seeds showed more pronounced shear-thinnin g. The viscosity of Nicotiana XG at 5% w/v was almost equivalent to ta marind seed XG at 0.5% w/v, displaying Newtonian behaviour. Modificati on of the molecular weight of the XGs and their degree of branching re vealed that differences in viscosity between the molecules, and their shear-field behaviour, was due primarily to differences in molecular w eight. Removal of fucose residues from apple pomace XG decreased the v iscosity of solutions from 8 to 4 mPa.s, whereas removal of both fucos e and galactose from apple pomace XG, resulted in precipitation from s olution. Deacetylation of Nicotiana XG also resulted in precipitation from solution. (C) 1998 Elsevier Science Ltd. All rights reserved.