FRACTIONATION AND PHYSICOCHEMICAL STUDIES OF SOME ACACIA GUMS

Abstract

Characterization and emulsification properties of Acacia Senegal, Acacia Seyal, Acacia Polyacantha gums and their fractions were studied using physicochemical methods. The results show that the average value of moisture, ash, pH, nitrogen and protein content of Acacia Senegal were found to be 11.01 %, 4.89, 4.78, 0.15% and 2.16 % respectively. For Acacia Seyal they were found to be 11.10%, 4.47%, 5.16, 0.22 % and 1.44% respectively, while for Acacia Polyacantha were found to be 10.48%, 4.48 %, 5.72, 0.38% and 2.50% respectively. The specific rotation, intrinsic viscosity, number average molecular weight, acid equivalent weight and total uronic acid of Acacia Senegal were found to be, -30°, 18.87g.ml-1,1.02X105g.mol-1, 1620 and 11.98 % respectively. For Acacia Seyal they were found to be +52°, 15.47 g.ml-1, 0.94 X105 g.mol-1, 1180 and 16.43 % respectively, while for Acacia Polyacantha were found to be -17°, 18.98 g.ml-1, 0.56 X105 g.mol-1, 1741 and 11.15 % respectively. Cationic composition studies (using atomic absorption technique) show that Potassium has the higher value followed by Calcium, Magnesium and Sodium. A number of fractions of Acacia Senegal, Seyal and Polyacantha were obtained by successive solvent fractionation technique by using ethanol and acetone as fractionating agent. The fractions were found to have different characteristics than the whole gums indicates the some variation in the molecular structure after fractionation.The molecular weight distribution of the Acacia gum samples and their fractions were determined by GPC-MALLS. The results show that three main components designated arabinogalactan protein (AGP), arabinogalactan (AG) and glycoprotein (GP). The weight average molecular of Acacia Senegal ranged from 8.078 X 105 - 1.334 X 106 g.mol-1 with Mw/Mn ranged from (2.89-4.42). The molecular weight of Acacia Seyal var Seyal ranged from 6.402 X 105 -1.78 X 106 g.mol-1 with Mw/Mn ranged from 2.631-3.552 and the GPC UV elution profiles demonstrated the protein was distributed in different fractions. The weight average molecular weight of Acacia Polyacantha ranged from 3.897X105-2.015 X 106 g.mol-1 with Mw/Mn ranged from (1.2-9.07) and the UV response show that small fractions with a low molecular weight contain high protein ratio. All ethanol and acetone fractions of Acacia Senegal show lowest degree of polydispersity than the starting material indicating good uniformity and increase adsorption of protein on the oil droplet surface. Emulsion stability index of ethanol fractions of Acacia Senegal are in the order SG-F3E> SG-F2E> SG-F1E> SG-F4E > SG-F5E> SG-control. Acetone fractions are in order SG-F1A> SG-F3A> SG-F4A> SG-F5A> SG-control> SG-F2A. Ethanol and acetone fractions of Acacia Polyacantha do not contribute any significant activity (poor emulsifier) as pure Acacia Polyacantha. ASY-F2E, ASY-F3E, ASY-F3A and ASY-F4A show better emulsification properties than the starting material. The emulsion stability of ethanol fractions of Acacia Seyal are in order ASY-F3E> ASY-F2E> ASY-F4E> ASY-control> ASY-F1E. Acetone fractions are in order ASY-F3A> ASY-F4E> ASY-F2E> ASY-control> ASY-F1E Blend of SG-PO 80/20% show better emulsification properties compared to the pure gums.