Physicochemical properties of Combretum glutinosum gum

Abstract

Characterization and emulsification properties of Combretum glutinosum gums and their fractions were studied using standard physicochemical methods. The results show that the average value of moisture, ash, pH, water capacity, Refractive index, nitrogen and protein content of Combretum glutinosum were found to be 9.88%, 4.32%, 4.79, 63.03%, 1.29, 0.198% and 1.316% respectively, while the solubility of Combretum glutinosum gum in water ranged from 30 to 40% with a gel fraction ranged from 60 to70%. Solubility of gum increased with increasing pH of the solution. The equivalent conductivity, acid equivalent weight and total uronic acid of Combretum glutinosum were found to be 354.11 s g-1cm2, 1291.71%, 15.54% respectively, thermal analysis show endothermic peak ranged from 30-45oC combined with heat content value of 0.3 – 1.5 J/ gm. Cationic composition studies shows that calcium, potassium, and magnesium value 1.27, 0.71, and 0.42 % w/w respectively, and the presence of mineral composition effected on gum solubility. Viscosity and dynamic rheological studies show Combretum glutinosum gum is an ionic polysaccharide, in contrast to gum Arabic which is neutral polysaccharide. The Combretum glutinosum solution has higher viscosity than that of the same concentration of gum Arabic solution, and the viscous activation energy of aqueous solution of the samples has an average value 18.78 kJ / mol, therefore, the viscous activation energy of the gum solution in molar sodium chloride and sodium hydroxide are 17.327 and 18.225 kJ / mol respectively. Emulsification studies of the gum fractions were shown lowest degree of span value than the starting material indicating good uniformity and increase adsorption of protein on the oil droplet surface. The molecular weight distribution of the gum samples and their fractions were determined using GPC-MALLS. The results show three main components designated arabinogalactan protein (AGP), arabinogalactan (AG) and glycoprotein (GP). The weight average molecular of the Native gum ranged between 2.06×106 to 9.73×105 gm /mol, for the deacetylated gum the weight average molecular ranged between 8.03×105 to 5.41×105 gm /mol, also the weight average molecular of calcium free gum sample is 1.40×106 gm/mol. The weight average molecular of of hybophilic and hybophobic fractions collected from Native gum are 3.16×106 and 6.08×105 respectively, while the weight average molecular of of hybophilic and hybophobic fractions collected from deacetylated gum are 1.39×106 and 8.36×105g/mol respectively. The results of emulsion studies show that a blend 50% w/w deacetylated Combretum glutinosum gum and 50%w/w Acacia Senegal show better emulsification properties than the pure gums.