Suspensions of cellulose microfibrils from sugar beet pulp

The chemical composition of sugar beet pulp (SBP) was analyzed. In addition to some mineral, this product consisted essentially of polysaccharides with about one third cellulose, one third hemicellulose and one third pectin. After a mild alkaline disencrusting and bleaching treatments, most of the hemicelluloses and pectins could be removed to yield a cellulosic residue that presented itself as a dispersion of thin parenchymal cell-ghosts having ovoid or elongated shapes and dimensions ranging from 50 to 200 mu m. The origin of these elements was traced back to the anatomy of the sugar beet root which was also investigated by scanning electron microscopy after critical point drying. At the ultrastructural level, the disencrusted SBP cell-ghosts consisted of a loose network of cellulose microfibrils, typical of parenchymal cell cellulose (PCC). This network could be disrupted by homogenization with a Manton-Gaulin apparatus to yield aqueous suspensions of either individual or bundles of cellulose microfibrils. This cellulose was characterized in terms of crystallinity, average degree of polymerization and chemical composition. The PCC suspensions did not flocculate nor sediment as long as some hemicellulose and pectin was maintained at the microfibril surface. Flocculation, however, occurred if these encrustants were removed by either strong alkali or a trifluoroacetic acid (TFA) treatment. (C) 1999 Elsevier Science Ltd. All rights reserved.