Analytical and structural studies of plant gum exudates

Studies presented in this Thesis fall into four distinct groups:1. Analytical characterizations have been made of the gum exudates from: (a) Eight species of the Series Gummiferae and Vulgares and three highly proteinaceous species of the Series Juliflorae of the genus Acacia; (b) Six species from the genus Leucaena which are chemically very close to gum arabic; (c) Nine specimens of gum obtained from Combretum nigricans growing in different locations; (d) Six A. senegal gum samples from Uganda and a further six "gum arabic" samples from different regions; (e) Seventeen species of gum exudates from 15 different genera such as Cassia grandis, Cercidium praecox, Parkia nitida, Prosopis chilensis, Sesbania sesban, Atalaya hemiglauca, Sclerocarya birrea, Pseudocedrela kotschyi, Senna nicaraguensis, etc..2. A study of some of the structural features of Combretum nigricans gum by Smith -degradation showed that uronic acid and rhamnose groups occur in internal locations within the overall structure, and not as end -groups as is the case in gum arabic (A. senegal).3. Amino acid data and ¹³C NMR spectra are presented for various fractions of A. senegal gum and for some highly proteinaceous Acacia gums (e.g. A. difficilis, A. eriopoda, A. tumida). The effect of enzymes on these gums is reported.4. ¹³C NMR spectra for thirty different gum exudates are presented to show the characteristic "fingerprint" patterns given by their polysaccharide structures. Information concerning their component monosaccharides, anomeric configurations, and linkages between the various sugar residues is given by spectrum analysis. This provides a most sensitive way to identify botanical species based on the total structure of exuded gums. The arabinose form (pyranose or furanose) and the various linkage configurations (α or ß) in the gum structures are important and directly affect the physico-chemical behaviour of gum exudates. Acacia gums in which rhamnose is absent (or nearly absent) generally have a large proportion of ß-L- arabinopyranose (A. seyal, A. sieberana, A. arabica gums etc.). The major arabinose form is α-L-arabinofuranose in gum arabic (A. senegal) whereas it is ß-L- arabinopyranose in gum tahla (A. seyal)