Studies on Acacia gums: Part III molecular weight characteristics of Acacia seyal var. seyal and Acacia seyal var fistula

Seventy four authenticated A. seyal samples have been studied in order to establish the molecular characteristics of this important species and the differences between the two variants A. seyal var. seyal (ASS) and A. seyal var. fistula (ASF) belonging to the Gummiferae series. Comparison is thus possible with A. senegal from the Vulgares series. The weight average molecular weight of A. seyal is at least three times greater than A. senegal. From average values ASF has a significantly higher molecular weight than ASS, contains less protein and more inorganic ash residue. Yet despite the high molecular weight, the intrinsic viscosities of ASF and ASS are less than for A. senegal, indicating a more compact molecular structure, which is supported by the root mean square radii measurements giving molecular size ratios of A. seyal to A. senegal of 0.77–1. The protein distribution in A. seyal is different, and whereas the protein in A. senegal is mainly associated with the high molecular weight component (AGP∼106) it is distributed differently and mainly associated with a lower molecular weight component in A. seyal. The Mark-Houwink plots for A. senegal confirm the differences in shape and size compared with A. seyal. The average molecular weight for ASF is 2.1×106, for ASS 1.7×106 compared with an average value of 0.6×106 for AS.