The classification of natural gums. VI. Gum arabic derived from Acacia Senegal var. Kerensis from Kenya

Abstract

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 from four regions of northern Kenya: Marsabit (Ngurunit), Marsabit (Kargi), Isiolo district and Turkana district and brown samples of gum from single trees from the various districts. The gums were analysed for amino acid composition, and physical and carbohydrate parameters: specific optical rotation, viscosity, % nitrogen and composition of galactose, arabinose, rhamnose, equivalent weight and uronic acid content. The mean [α] D varied from −34 to −37°, with individual values of −40° recorded; the average nitrogen content was 0.45%, with individual samples as high as 0.70%. 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 commercial gums arabic and authenticated A. senegal samples collected from a variety of countries: Sudan, Niger, Nigeria, Uganda, Oman, Mauritania, Mali, Senegal and Ethiopia. The gums were drawn from periods ranging 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 gum arabic/ A. senegal from the various countries. Gums from the Marasbit (Kargi) region, mainly contributed to a peripheral cluster characteristic of the Kenya gum. The physical and carbohydrate features also confirmed the fundamental similarity of the Kenya gum to the other gum arabic/ A. senegal samples. Here also a distinctive cluster could be attributed to certain Kenya samples, mainly from the Turkana region. When the carbohydrate and amino acid features are combined to provide 26 features, the former patterns were evident, with the amino acid compositions exerting the major influence on the cluster patterns. Using only four of the most discriminating features: specific optical rotation, viscosity, 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 certain groups of gums, we were able, by analysis of covariance, to identify the region of origin of such local variants within the gum arabic family. On the basis of the chemometric analytical evidence, the gum arabic derived from a varietal form of A. senegal found in Kenya must be regarded as a legitimate and acceptable gum arabic.