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Bangor University (1994)

The availability, quality and processing aspects of gum arabic from Kenya

Chikamai, Elijah Nandi Ben

Titre : The availability, quality and processing aspects of gum arabic from Kenya

Auteur : Chikamai, Elijah Nandi Ben

Etablissement de soutenance : Bangor University

Grade : Doctor of Philosophy (PhD) 1994

Four aspects on gum arabic from Kenya were examined in this Thesis ; resource availability, physical and chemical properties, evaluation of methods for monitoring and quality control and processing. Under resource availability, provisional Acacia sehegal maps were produced showing that the resource occupies 14%, 2O% and 37% of Isiolo District, south western Marsabit and Turkana Districts respectively. The main source of gum arabic was identified as A. senegal var. kerensis and was observed growing mostly in patches with high stocking on hills and occasionally along luggas (dry river streams). The relative amount of resource available for tapping varied between the three districts with Turkana District having the highest proportion and Isiolo District the least. The species grows in association with some of the other gum producing species. Acacia seyal and A. tortilis were recognised as the main species likely to produce gum in large quantities and thus possible contaminants. Studies on characterisation of Kenyan gum (from var. kerensis) showed that it differs from the present commercial gum (from var. senegal) in specific rotation, nitrogen content and intrinsic viscosity showing that the taxonomic differences observed are well reflected in the chemical nature of the two varieties. Variations were also observed between samples and regions and were attributed to possible genetic effects and local adaptations respectively. These differences present future opportunities for improving gum production through tree improvement and gum handling practices. In terms of emulsification functionality, - Vll - gum arabic from var. kerensis was comparable and in most cases gave better results than gum from other commercial sources. An evaluation of methods regarded as inexpensive for monitoring and quality control revealed that elution profiles produced by gel permeation chromatography (gpc) method provide a quick and consistent diagnosis of gum arabic of commerce. The use of physico-chemical and carbohydrate (analytical) method is also useful but tends to be influenced more by natural product variability and can sometimes result in rejection of otherwise authentic gum arabic. The Enzyme linked immunosorbent assay (Elisa) technique is useful but needs further refining to make it more specific to gum arabic from A. senegal. Results on processing of gum arabic showed that heating gum solution at 100°C results in significant degradation of the gum molecule after 6 hours affecting emulsification functionality and that heating at 65°C seems to be a favourable alternative. Use of enzyme biotechnology has a promising future. All the three enzymes examined degraded the gum molecule but with different effects on the resulting gum properties. The protein degrading enzyme (pronase) has a fast rate of reaction causing reduction in viscosity and gelling but the gum also loses its emulsifying functionality. The two carbohydrate degrading enzymes (viscozyme and ß-D-galactosidase) achieve the desired reduction in viscosity and gelling at about the same rate. However, the former slightly degrades the protein component resulting in unstable emulsions while /3-D-galactosidase gave better results. On the basis of these studies, areas for future attention are suggested.

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