The amino acid composition and quantitative sugar‐amino acid relationships in sequential Smith‐degradation products from gum arabic(Acacia Senegal(L.) Willd.)

Abstract

Data are presented for the amino acid composition of gum arabic, i.e. the exudate from Acacia senegal (L.) Willd., and for its four sequential Smith‐degradation (SD) products (0.34, 0.56, 0.87, 0.90 and 0.85% N respectively). The molar polysaccharide/protein ratio in the whole gum (31:1) decreased to 11:1 in its fourth SD product which is a proteinaceous branched galactan; proline, hydroxyproline, serine, thrèonine and leucine account for 82% of its amino acids. The first SD eliminated large amounts of sugars and small amounts of amino acids (molar ratio 40:1). The second, third and fourth degradations eliminated all of the arabinose, rhamnose and uronic acid, and 87% of the galactose originally present (molar ratios for the sugars/amino acids eliminated=42:l, 12:1 and 8:1 for SD‐II, SD‐III and SD‐IV respectively). Overall (four SD stages), 94% of the original sugars but only 85% of the amino acids was eliminated. The proteinaceous enrichment of the galactan core largely involved serine, threonine and proline, but hydroxyproline accounts for c.30% of the amino acid content of the whole gum, SD‐III and SD‐IV, and c.45% of SD‐I and SD‐II. As deduced in a recent study of the gum from the closely related species Acacia polyacantha there are indications that amino acids are associated with the sugars involved in the interior of the complex molecular gum structure.