EFFECT OF ISOLATION PROCEDURES ON THE MOLECULAR COMPOSITION AND PHYSICAL-PROPERTIES OF EUCHEUMA-COTTONII CARRAGEENAN

Direct treatment of Eucheuma cottonii with hot potassium hydroxide lea ds to a solid residue (alkali treated weed) which was found to contain predominantly carrageenan and cellulose. Following dispersion and hea ting iri water, separation into polymer-containing solution and an ins oluble particulate phase was readily achieved. Chemical analysis of so lubilized polymers showed that the predominant carrageenan present in native weed was a mu/kappa-carrageenan which was readily converted int o kappa with hot alkali. The particulate phase from both materials was predominantly cellulose; characterization by X-ray diffraction showed the presence of partial cellulose type I crystallinity. Solid state C -13-NMR spectra showed that this crystalline fraction was similar to 5 3% of the total cellulose and was comprised of similar to 40% type I a lpha and similar to 60% type I beta. The cellulosic part seemed unaffe cted by the hot alkali treatment. A carrageenan type polysaccharide wa s found associated with the cellulosic fraction; which underwent the s ame conversion as the mu/kappa carrageenan on alkali treatment. Furthe r refining of solubilized carrageenan by isopropyl alcohol precipitati on, gel pressing or freeze-drying, resulted in only minor differences in chemical composition. Hot solution viscosity and gelation propertie s in the presence of potassium chloride were measured showing no signi ficant differences in gelling behaviour between alkali treated weed an d the different carrageenan isolates but a higher solution viscosity f or the alkali treated weed.