The gum exudate from Combretum nigricans gum, the major source of West African ‘gum combretum’

Abstract

Gum samples from six individual Combretum nigricans trees and two additional reference samples have been characterized. ¹³C Fourier‐transform NMR spectra show that all have the same structure and confirm that the variations observed in their analytical parameters reflect only small fine‐structural differences. NMR spectra also reveal that eight West African ‘gum combretum’ samples from reputable commercial sources originated from Combretum nigricans. This identification is important because gum combretum, which is not permitted as a food additive, has been exploited as an adulterant and misrepresented as gum arabic, for which not even the 1990 Revised Specification is sufficiently rigorous to detect such commercial deceptions. NMR spectroscopy has also shown that the rhamnose and uronic acid contents of gum combretum are located within internal polysaccharide chains. This explains the well‐known difference in emulsification functionality between gum arabic, in which all rhamnose and uronic acid groups are chainterminal, and gum combretum which is, in addition, markedly hygroscopic and characterized commercially by its tendency to ‘block’ in transit and storage.

Keywords:

• NMR spectra
• gum combretum
• emulsification functionality
• Combretum nigricans