The availability, quality and processing aspects of gum arabic from Kenya. (1994)

Four aspects on gum arabic from Kenya were examined in this Thesis;&#13;\nresource availability, physical and chemical properties, evaluation of methods for&#13;\nmonitoring and quality control and processing.&#13;\nUnder resource availability, provisional Acacia sehegal maps were&#13;\nproduced showing that the resource occupies 14%, 2O% and 37% of Isiolo&#13;\nDistrict, south western Marsabit and Turkana Districts respectively. The main&#13;\nsource of gum arabic was identified as A. senegal var. kerensis and was observed&#13;\ngrowing mostly in patches with high stocking on hills and occasionally along&#13;\nluggas (dry river streams). The relative amount of resource available for tapping&#13;\nvaried between the three districts with Turkana District having the highest&#13;\nproportion and Isiolo District the least. The species grows in association with&#13;\nsome of the other gum producing species. Acacia seyal and A. tortilis were&#13;\nrecognised as the main species likely to produce gum in large quantities and thus&#13;\npossible contaminants.&#13;\nStudies on characterisation of Kenyan gum (from var. kerensis) showed&#13;\nthat it differs from the present commercial gum (from var. senegal) in specific&#13;\nrotation, nitrogen content and intrinsic viscosity showing that the taxonomic&#13;\ndifferences observed are well reflected in the chemical nature of the two varieties.&#13;\nVariations were also observed between samples and regions and were attributed to&#13;\npossible genetic effects and local adaptations respectively. These differences&#13;\npresent future opportunities for improving gum production through tree&#13;\nimprovement and gum handling practices. In terms of emulsification functionality, &#13;\n- Vll -&#13;\ngum arabic from var. kerensis was comparable and in most cases gave better&#13;\nresults than gum from other commercial sources.&#13;\nAn evaluation of methods regarded as inexpensive for monitoring and&#13;\nquality control revealed that elution profiles produced by gel permeation&#13;\nchromatography (gpc) method provide a quick and consistent diagnosis of gum&#13;\narabic of commerce. The use of physico-chemical and carbohydrate (analytical)&#13;\nmethod is also useful but tends to be influenced more by natural product variability&#13;\nand can sometimes result in rejection of otherwise authentic gum arabic. The&#13;\nEnzyme linked immunosorbent assay (Elisa) technique is useful but needs further&#13;\nrefining to make it more specific to gum arabic from A. senegal.&#13;\nResults on processing of gum arabic showed that heating gum solution at&#13;\n100°C results in significant degradation of the gum molecule after 6 hours affecting&#13;\nemulsification functionality and that heating at 65°C seems to be a favourable&#13;\nalternative. Use of enzyme biotechnology has a promising future. All the three&#13;\nenzymes examined degraded the gum molecule but with different effects on the&#13;\nresulting gum properties. The protein degrading enzyme (pronase) has a fast rate&#13;\nof reaction causing reduction in viscosity and gelling but the gum also loses its&#13;\nemulsifying functionality. The two carbohydrate degrading enzymes (viscozyme&#13;\nand ß-D-galactosidase) achieve the desired reduction in viscosity and gelling at&#13;\nabout the same rate. However, the former slightly degrades the protein component&#13;\nresulting in unstable emulsions while /3-D-galactosidase gave better results.&#13;\nOn the basis of these studies, areas for future attention are suggested.