COMBRETUM NIGRICANS GUM – ITS UNUSUAL STRUCTURE/PROPERTIES AND DIFFERENCES FROM GUM ARABIC (ACACIA SENEGAL)

SUMMARY Combretum nigricans is the major source of commercial “gum combretum” which is widely available in West African markets. Although not permitted in foodstuffs by regulatory authorities it has been used as an adulterant of gum arabic (Acacia Senegal) with adverse results because the desirable properties of the latter are thereby greatly reduced. Gum combretum itself has an unfortunate reputation for self-adhesion to form “blocked” gum, although it is desirable for some commercial applications if stored and used appropriately. 13C Nuclear magnetic resonance spectrometry and degradative procedures have shown the essential difference in chemical structure involved; the constituent rhamnose and uronic acid units, which occupy peripheral, chain-terminal structural positions in gum arabic, are located in internal positions in gum combretum.