Abstract

Powdered Grewia species barks was extracted in water and one part of the extract was precipitated with absolute ethanol. Both the crude water extract and the ethanol precipitate were freeze dried, pulverized into powder and subjected to physicochemical analyses. Amongst others, proximate composition, morphology and metal contents by Scanning Electron Microscopy with Energy Dispersive X-Ray (SEM-EDX), functional group by Fourier-transform infrared spectroscopy (FTIR), crystallinity by X-ray powder diffraction (XRD), thermal behavior via Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The molecular mass of the ethanol precipitate was appraised through viscosity measurements and the Huggins plot. Results show that both the crude extract and the ethanol precipitate were rich in polysaccharide type polymers. However, precipitation led to a reduction in the metal contents confirmed by the ash contents and the EDX analysis as well as the absence of sharp peaks on the XRD plots as was the case of crude extracts. Precipitation led to a decrease in the lipid and protein contents initially present in the crude Grewia spp. extracts. XRD and SEM analyses revealed that Grewia spp. extract and the precipitate were both amorphous with a porous microstructure. Results also showed that Grewia spp. biopolymer has functional groups which can serve as active sites for the attachment of colloidal particles.

Key words: Grewia species, biopolymer, extraction, precipitate, characterization.