Rheology and Stability of Emulsions of Some Acacia Gums and Their Blends

Abstract

Four Authentic representative gum exudate samples from Acacia species namely Acacia senegal var. senegal (ASG), Acacia mellifera (AMF), Acacia seyal var. seyal (ASY), and Acacia tortilis var. raddiana (ATR), were characterized. The moisture, ash, nitrogen, protein content, pH, specific optical rotation, and number average molecular weight were found to be 9.76, 3.40, 0.327, 2.158, 4.94, -31.75, and 0.24x106 for ASG, 9.56, 2.5, 0.630, 4.158, 4.53, -48.25, and 2.10x106 for AMF, 8.35%, 3.13, 0.243%, 1.610%, 4.84, +56.00, and 2.95x106 for ASY and 8.49%, 2.05, 1.549%, 10.378%, 4.45, +86.75, and 2.06x106 for ATR respectively. The 13C and 1H NMR spectra of gum samples showed similarity in individual sugars components, but characteristic patterns of each gum, were observed. The same functional groups were observed from the FTIR spectra of the gums. DSC and TGA thermograms were characteristic for each gum. ASG, AMF, ASY, and ATR gum emulsions were prepared, without the addition of weighting agents, using different concentrations of Isopropyl Myristate (IPM). ASG and AMF gums from the Vulgares series and ASY and ATR gums from the Gummiferae series were blended in different proportions. Blends emulsions were prepared with 20% IPM oil concentration. The morphology of gums and blends emulsions; over seven days of incubation at 45C, exhibited spherical and dense droplets. Particles size measurements, over a period of four weeks of incubation at 45C, showed that ATR v gum formed smaller and more stable droplets compared to the other gums. Phase separation was observed at low oil concentration for all gum emulsions. Emulsions of blends showed remarkable stability. The dye test confirmed that all gums and blends emulsions are oil in water (O/W) system. The rheological flow profiles of gums solutions at varying concentrations reflect a Newtonian flow for 50% and 40% concentrations and shear-thinning flow behavior for 30% and 20% concentrations. All gums and blends, O/W, emulsions showed oil’s concentration dependence; their profiles exhibited a shear-thinning flow behavior and a Newtonian flow beyond 100 s-1 shear rate suggesting the alignment, of gums molecules, with shear direction. The dynamic rheological study showed moduli frequency dependence pattern for gum dispersions, gum emulsions, and blend emulsions suggesting network formation of the gum molecules around the oil droplets of the emulsions.