THE CLASSIFICATION OF NATURAL GUMS .6. GUM-ARABIC DERIVED FROM ACACIA-SENEGAL VAR KERENSIS FROM KENYA

Sixty-seven samples of gum from Acacia senegal var. Kerensis, the main source of gum arabic in Kenya, have been evaluated using chemometric methods. The gums were collected from individual authenticated trees f rom four regions of northern Kenya: Marsabit (Ngurunit), Marsabit (Kar gi), Isiolo district and Turkana district and brown samples of gum fro m single trees from the various districts. The gums were analysed for amino acid composition, and physical and carbohydrate parameters: spec ific optical rotation, viscosity, % nitrogen and composition of galact ose, arabinose, rhamnose, equivalent weight and uronic acid content. T he mean [a], varied from -34 to -37 degrees, with individual values of -40 degrees recorded; the average nitrogen content was 0.45%, with in dividual samples as high as 0.79%. On this basis the gum fell outside the proposed JECFA limits, and if this specification was implemented, the Kenya gums would not be acceptable as commercial gum arabic. Using principal component (PCA), the Kenya gum was compared to 65 other com mercial gums arabic and authenticated A.senegal samples collected from a variety of countries: Sudan, Niger, Nigeria, Uganda, Oman, Mauritan ia, Mali, Senegal and Ethiopia. The gums were drawn from periods rangi ng from 1903 to the present. On the basis of amino acid analysis, all the Kenya gums formed part of an extended cluster which embraces the g um arabic/A.senegal from the various countries. Gums from the Marasbit (Kargi) region, mainly contributed to a peripheral cluster characteri stic of the Kenya gum. The physical and carbohydrate features also con firmed the fundamental similarity of the Kenya gum to the other gum ar abic/A.senegal samples. Here also a distinctive cluster could be attri buted to certain Kenya samples, mainly from the Turkana region. When t he carbohydrate and amino acid features are combined to provide 26 fea tures, the former patterns were evident, with the amino acid compositi ons exerting the major influence on the cluster patterns. Using only f our of the most discriminating features: specific optical rotation, vi scosity, hydroxyproline and lysine, both the distinctive nature of the Kenya gums and their broad coherence within the gum arabic family was established. Using the dominant characteristics associated with certa in groups of gums, we were able, by analysis of covariance, to identif y the region of origin of such local variants within the gum arabic fa mily. On the basis of the chemometric analytical evidence, the gum ara bic derived from a varietal form of A.senegal found in Kenya must be r egarded as a legitimate and acceptable gum arabic.