Studies on Acacia exudate gums: part II. Molecular weight comparison of the Vulgares and Gummiferae series of Acacia gums

Representative samples from the Vulgares and Gummiferae series of Acacia exudate gum were compared using combined gel permeation chromatography and multi-angle laser light scattering (GPC-MALLS). For the Vulgares gums, there is a much lower proportion of the higher molecular weight component compared to the Gummiferae. A. karoo and A. sieberana, both from the Gummiferae series, showed the highest average molecular weight of 2.99 and 7.10×106, respectively. For these, the higher molecular weight component which eluted in peak 1 is in greater amount (∼60%). The average molecular weight for A. seyal is greater than that of A. senegal and the average value of the Vulgares gums. There is a reasonable uniformity within the Vulgares series, whereas the variation is greater for Gummiferae gums in keeping with their wider taxonomic origin and development. This conforms with the wider chemometric distribution within the Gummiferae grouping compared to Vulgares gums. Despite the higher overall molecular weights of the Gummiferae gums, their intrinsic viscosities are generally lower, indicating a more compact structure than the more coherent Vulgares gums.