Physiochemical Studies on the Gum from Acacia tortilis var. raddiana

Abstract

Twenty eight authentic samples from Acacia tortilis var. raddiana gum were collected as natural exudates from two locations in Sudan, (Abo shmal-south east of Khartoum and Algetana- south west of Khartoum) on February of 2008, 2009 and 2010. Characterization of A.tortilis var. raddiana was undertaken so that physical and chemical properties such as moisture content, ash content, specific optical rotation, nitrogen and protein content, acid equivalent weight and total glucuronic acid, refractive index, pH and molecular weight were determined. Results show insignificant differences within each location in, almost all, parameters studied. Acacia tortilis var. raddiana was found to contain average moisture of 11.8 (w/w), average ash content was 1.8%. The nitrogen content was 1.6%, the nitrogen conversion factor was 6.72 and the protein content was 11.24% (w/w) in average. Acacia tortilis var. raddiana exhibited dextrogyrate optical rotation with specific rotation ranging between (+78.26) – (+91.63). The acid equivalent weight and glucuronic acid content were found to have values of 1944 and 10.01 respectively. Molecular weight of A. tortilis var. raddiana was estimated from light scattering measurement using multi-angle laser light system. The average molecular weight was found to be 1.35x106. The radius of gyration was also estimated and found to have an average 32.5 nm. This reflects the compact structure of A.tortilis var. raddiana molecule. The highly molecular weight of A.tortilis var. raddiana and its high water solubility suggest a highly branched structure. Fractionation of A.tortilis var. raddiana gum using gel permeation column coupled to multi detector system comprising light scattering. RI and UV gave insight of distribution of molecular fraction of the gum molecule. The resultant chromatogram showed the protein was distributed between the fractions and mainly associated with lower molecular mass fraction in the polymer molecule, the molar mass fractions distribution pattern produced for A.tortilis var. raddiana differed from that obtained A.senegal var. senegal and A.seyal var. seyal which the protein in both of them associated with high molecular mass fraction. Emulsification studies showed that A.tortilis var. raddiana possess a high emulsifying power as its oil-in-water emulsion possessed smaller droplet size compared to those of A.senegal var. sengal gum. A.tortilis var. raddiana gum showed a good emulsifying stability. Rheological study showed that the gum from A.tortilis var. raddiana behave as a Newtonian fluid and showed shear thinning under simple shear and oscillatory deformation regimes.