Preparation and Physicochemical Characterization of Glucuronic acid and Glucuronates Salt from

Abstract

Preparation and physicochemical characterization, emulsification and rheological properties of glucuronic acid and glucuronates from Acacia senegal var senegal gum were studied using standard methods. Standard characterization methods were used to obtain average value of moisture, ash, specific rotation, intrinsic viscosity, pH, nitrogen, protein, number average molecular weight, acid equivalent weight and refractive index of Acacia senegal var senegal gum, they were found to be 8.42%, 3.5%, -24.87°, 12.0 ml g-1, 4.6, 0.35%, 2.23%, 4.1×105 Da ,1239.6 and 1.336 respectively. The sugar composition study using HPLC technique shows the percentage of the average values of galactose, arabinose, rhamanose and glucuronic acid for Acacia senegal var senegal gum, the values were found to be 40.70, 33.79, 9.31 and 15.65 respectively. The cationic composition study using atomic absorption technique shows that calcium has the highest value followed by, potassium, magnesium and sodium. As for the rest of the elements namely Fe, Cu and Zn only trace values were obtained for the gum Acacia senegal var sengal. Glucuronic acid was prepared from Acacia senegal gum by the removal of metal ions using ion exchange chromatography. Glucuronates of (Na, K, Ca and Mg) were prepared using glucuronic acid by adding respective cations. Scanning electron microscope (SEM) proved successful production of glucuronic acid and glucuronates. The measured pH values were 2.6, 6.9, 6.5, 4.9, and 4.5 for glucuronic acid, Na, K, Ca and Mg glucuronates respectively. Intrinsic viscosities of glucuronic acid, Na, K, Ca and Mg glucuronates in 1M NaCl were determined. The iv measured viscosities were 8.53, 2.47, 0.11, 0.05 and -1.24 ml g-1 for glucuronic acid, Na, K, Ca and Mg glucuronates respectively and 10.82, 14.33, 12.9, 10.12 an d 9.38 ml g-1 for glucuronic acid, Na, K, Ca and Mg glucuroniates respectively in 0.5M NaCl where they were 18.47, 45.82, 30.72, 11.76 and 10.83 ml g-1 for glucuronic acid, Na, K, Ca and Mg glucuronates respectively in deionized water. The intrinsic viscosity have been measured in dilute 3% concentration and pH of 5.5 and the results were 118.37, 116.73, 21.27, 18.91 ml-1 for Na, K, Ca and Mg glucuronates respectively. The equivalent conductivities of glucuronic acid and glucuroniates have been measured in water at 25°C. The results showed a very sharp nonlinear increase with decreasing polyelectrolyte concentration. The rheological study of the Acacia senegal gum and glucuronates show Newtonian behavior with linear relationship between stresses and shear rate while glucuronic acid show non-Newtonian behaviour (Pseudoplastic) and hence it is shear thinning. The study also show viscous behaviour of the gum with G'' dominate G' in the lower region of the frequency range tested; viscous behaviour of the Acacia senegal gum and glucuronates dominates the elastic behaviour. After a certain frequency a cross-over of G' and G" is seen; as frequency increase G′ < G''. glucuronic acid show different behaviour G' and G" profiles are parallel (no cross-over) with G′ > G′′. The emulsion of Na, Ca and Mg show stability until 3 days while Acacia senegal gum form multiple peaks from 3 days and completely separated in 7 days. The emulsion of K and glucuronic acid results clearly showed that no change was found in emulsions during the incubation for 7 days at 60oC which means that they have better emulsifying properties over the time range and temperature.