Degradative studies of highly proteinaceous Acacia gum exudates

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Abstract
Solutions of the gums from Acacia gerrardii, A. goetzii and A. tumida (percentage N = 1.86, 0.89 and 7.66 respectively) have been subjected to mild acidic hydrolysis; a solution of the gum from A. eriopoda (percentage N = 6.70) has been subjected to ultraviolet irradiation and acidic hydrolysis. Data are presented for the sugar and amino acid compositions of the three products obtained from each gum by the degradative processes used. The results extend those obtained previously for Acacia Senegal gum; acidic hydrolysis and ultraviolet irradiation gave differing yields of the insoluble and dialysate fractions having different analytical parameters. The hydrolysis of A. tumida gum gave a large amount of insoluble proteinaceous material but no dialysate. After mild acidic hydrolysis, rhamnose appeared predominantly in the insoluble proteinaceous fractions from A. gerrardi, A. tumida and A. eriopoda and, in contrast, in the essentially non‐proteinaceous dialysate from A. goetzii gum. As established for Acacia Senegal (gum arabic), some amino acids, e.g. alanine, aspartic acid, glutamic acid, and glycine are more labile than others to degradative processes: the main effect is for the high proportions of serine and hydroxyproline in the natural gums to become even higher in the degraded gums. These results indicate fine structural differences between the gums studied, and differences in the relative stabilities of their amino acids and sugars. This provides a basis for a clearer understanding of some phenomena, associated with the fragility of gum arabic, that were not clearly understood previously.