CHARACTERIZATION AND ANALYTICAL STUDIES OF ACACIA POLYACANTHA

Abstract

Acacia Polyacantha gum samples were collected as natural exudates, from three different locations, namely Abugarin and Gargadah (season 2000/2001and2001/2002) and Layoon forest (season (2000/2001). Physicochemical properties of gum samples were studied (moisture, ash, nitrogen, protein, specific rotation, intrinsic viscosity, refractive index, equivalent weight, pH, uronic acid and reducing sugar). Results show insignificant differences within each location in all parameters studied. The effect of location on the properties of gum samples was also studied and the analysis showed insignificant differences in all properties studied. Molecular weight of A. Polyacantha gum was estimated from light scattering measurement using multi – angle laser light system. High molecular weight of A. Polyacantha and its high water solubility, the value of weight average molecular weight (Mw) and number average molecular weight (Mn) was found to be 2.84105 and 1.369x105 respectively. The high molecular weight of A.Polyacantha and, it is high water solubility suggest a highly branched structure. The general characteristics of A. Polyacantha gum are the mean values of all properties studied for all gum samples from the three different locations are as follow: 8.2% moisture, 2.9% ash, 0.35% nitrogen, 2.31% protein, -16.6 ospecific rotation, 10.34ml/g intrinsic viscosity, 4.9 pH, 1.3337 refractive index, 14.50%uronic acid, 1361 equivalent weight and 0.21reducing sugar. UV absorption spectra of gum samples were determined and the maxima were found to be approximately the same. Cationic composition of gum samples was also determined and the results show that sodium (Na) has the highest value in all samples studied followed by iron (Fe), zinc (Zn), nickel (Ni), copper (Cu), manganese (Mn), calcium (Ca), magnesium (Mg), lead (Pb) and potassium (K). Some structural features of A. Polyacantha gum were also studied. The component sugars of the gum were determined by using different methods (Fractionation, Acid hydrolysis and Autohydrolysis), which were, followed qualitative analysis. Fractionation of A. Polyacantha gum using acetone gave five different fractions. Some physicochemical properties of the fractions were studied. Results show insignificantly differences in all parameters studied, except the refractive index was found to be constant (1.3337). Fractionation of A. Polyacantha gum using gel permeation column coupled to a multi- detector system comprising light scattering, RI and UV detectors gave insight of the distribution of the molecular fractions of the gum molecule. The resultant chromatogram shows a high molecular weight fraction associated with much of the protein present in the polymer molecule, a low molecular mass fraction of much lesser amount of protein and a low molecular mass proteinaceous fraction. The molar mass fractions distribution pattern produced for A. Polyacantha differed from that obtained for A. Senegal gum. However the patterns of the two gums differed in the proportion of each fraction. Comparing the three gum samples using the three different detectors revealed that the sandy soil samples (Layoon forest) show higher molecular fraction than that of the clay soil (Abugarin and Gargadah). A.Polyacantha gum was hydrolysed using sulphuric acid at different concentrations (0.5N and 1.0 N) and also at varying time of hydrolysis (6 to 8 hours). Results show that acid hydrolysis at different concentrations gave approximately the same monosaccharides (L- arabinose, D- galactose, L- rhamnoses and D - glucuronic acid). 13 CNMR for the dialysed A. Polyacantha gum indicated the presence of 4, 6 -α - rhamnopyranose, 4,5-α-L-arabinofuranose, 1,2,5 - β -D - galactopyranose and 1, 6 - β - D - glucopyranuronic acid. Emulsification studies show that A. Polyacantha gum posses good emulsifying stability. However the emulsifying stability of the emulsions of A.Polyacantha gum is less than that of A. Senegal. Blending of A. Polyacantha and A. Seyal was explored and it was found that a mixture containing 25%A. Polyacantha and 75% A. Seyal produced a gum blend having a better emulsifying stability compared to the pure gums.