抄録
The series of control Acacia senegal gums and the samples which had been matured to produce the Acacia (sen) SUPER GUM™ samples (FR-2877, FR-2878 FR-2879, EM1 and EM2) were examined by NMR, FT-IR spectroscopy and dynamic light scattering. No chemical difference in any of the samples could be detected by 13CNMR or 2D NMR (COSY) spectroscopy. The 1H NMR and 1H NMR spectra confirmed these observations, but showed that at the highest level of maturation to average molecular weights in excess of 2.5 x 106, some changes could be observed, which probably is due to dehydration of the COOH uronic acid group. The selection of the matured gums for commercial use ensures that no observable changes are evident in these gums.
Dynamic light scattering data showed these gums are highly heterogeneous in molecular size. In extreme dilute solutions, two distinctively separated populations of particles were observed with the sizes of each group almost identical for the control gum (EM0) and SUPER GUM™ samples (EM1 and EM2) (~20 nm and ~70 nm, respectively). However, the relative amount of the larger size group was in the order of EM0<EM1<EM2, corresponding to an increase in molecular weight. On increasing the polymer concentration, the two groups seem to form aggregates of their own independently, giving two new groups of particles. The maturation treatment resulted in a significant increase in the size of the larger size group which suggests the maturation treatment not only increased the molecular weight of gum arabic, but also modified the surface properties of the molecules in a way that makes them more able to aggregate.
