Dynamic mechanical thermal analysis of cell wall polysaccharides extracted from lyophilised carrot Daucus carota

Dynamic mechanical thermal analysis (DMTA) was used to determine thermal phase transitions in low water content cell wall polymer mixtures extracted from lyophilised carrot tissue. The cell wall material was sequentially extracted to produce three residues: an extract free from Ca2+ pectic polysaccharides, an extract mainly free from pectic polysaccharides and a final residue rich in hemicellulose and cellulose. A single broad transition was found, the temperature of which decreased with increasing water content. The magnitude of the drop in storage modulus (E) at the transition increased with increasing water content, between 0 and 28% (wet weight basis, w.w.b). The values of E' taken at 20degreesC were similar for all the residues and were typical of a glassy material for the water range 0-20% (w.w.b). Above 20% (w.w.b), E' at 20degreesC decreased with increasing water content. As more amorphous material was removed during the sequential extraction, the residues became richer in hemicellulose and cellulose, sorption isotherms exhibiting a more hydrophobic behaviour than that of the whole cell wall. This study showed the dominant contribution of the hemicellulose/cellulose domain to the stiffness of lyophilised carrot cell wall at these low water contents. (C) 2002 Elsevier Science Ltd. All rights reserved.