Some properties of selected tree exudate gums from Tanzania.

This dissertation reports on the physical and chemical properties of gum exudates from three Albizia species and gum samples from Sterculia quinqueloba and Dichrostachys cinerea and compares them with established commercial gums. The properties of all the three Albizia gums studied compare favourably with the gum exudate from Albizia zygia. In addition, Albizia petersiana not only most closely resembles Albizia zygia but also meets a number of the specifications demanded by the regulatory bodies (JECFA/ FAO, 1990; British pharmacopoeia, 1980 and Food Chemicals Codex, 1981) for gum arabic for food and pharmaceutical applications. However, the results show that it contains tannin and has higher levels of nitrogen and ash contents. The main drawbacks of Albizia amara and Albizia harveyi as potential gum arabic alternatives, on the other hand, are their specific rotation being out of the specified range and higher insoluble gel, nitrogen and tannin contents. Moreover, the gum sample from Albizia amara possesses high levels of lead and manganese. The Albizia gums studied form highly viscous solutions at low concentrations, a property which has also been reported for gum ghatti. The gum exudate from Dichrostachys cinerea meets a large number (moisture content, solubility, insoluble matter, ash, lead, and heavy metals) of the specifications demanded for the identity and purity of gum arabic as stipulated in JECFA/ FAO (1990) and the British pharmacopoeia (1980), except for specific rotation, nitrogen and tannin contents. Unlike Albizia gums, it gives rise to aqueous solutions with viscosities and solubility comparable to commercial gum arabic. Similarly, the properties of Sterculia quinqueloba gum meets most of the specifications demanded for gum karaya, except that it contains high levels of tannin.