CHARACTERIZATION AND THERMODYNAMIC PROPERTIES OF GUMS OF ACACIA ORIGIN

Abstract

Characterization, thermodynamic, denaturation and mlocular expansion properties of A. seyal, A. senegal and A. polyacantha gums were studied using physicochemical methods. Characterization studies, which are partly used for authentication of samples and resources, included the determination of moisture, ash, nitrogen and protein content. The average amount of moisture, ash, nitrogen and protein content of A. seyal were found to be, 11.01 %, 2.43%, 0.144% and 0.95% respectively. For A. senegal they were found to be 11.07%, 3.32%, 0.368% and 2.43%, while for A. polyacantha were found to be 10.45%, 3.22 %, 0.256% and 1.69%. The intrinsic viscosities, specific rotation, acid equivalent weight and total uronic acid of A. seyal were found to be, 11.64 cm3 g-1, +60, 1185.77 and 16.36 % respectively. For A. senegal they were found to be 15.37 cm3 g-1, -31.5, 1153.85 and 16.81%, while for A. polyacantha were found to be 12.08 cm3 g-1, -8.5, 1724.14 and 11.25%. Cationic composition studies (using Atomic Absorption technique) show that potassium has the higher value followed by calcium, magnesium, sodium, iron and zinc. Sugar composition was estimated using HPLC technique, galactose content of A. seyal, A. senegal and A. polyacantha were found to be 28.78%, 29.68% and 37.94% respectively, and arabinose content were found to be 34.04%, 21.02% and 25.04% respectively. while rhamnose were found to be 1.61%, 10.14% and 6.67% respectively. Molecular weight of the samples was estimated using GPC-MALLS technique. The values of Mw and Mn of A. seyal were found to be 15.5x105 and 5.16x105. For A. senegal were found to be 8.64x105 and 2.86x105, while for A. polyacantha were found to be 3.18x105 and 1.43x105. The Mn was also determined by using osmotic pressure technique and was found to be 4.7x105, 2.4x105 and 1.9x105 for A. seyal, A. senegal and A. polyacantha respectively, the study shows that the results of the tow different methods are very close. The radius of gyration was also estimated and found to have values 38, 40 and 10 nm for A. seyal gum, A. senegal gum and A. polyacantha gum respectively. In the thermodynamic studies, the density, the partial specific volume of gum, partial specific volume of the solvent and the volume fraction were estimated, for A. seyal was found to be 1.485 g cm-3, 0.6426 cm3 g-1, 1.0016 cm3 g-1 and 0.3908. For A. senegal they were found to be 1.465 g cm-3, 0.6425 cm3 g-1, 1.0018 cm3 g-1 and 0.3907, while for A. polyacantha were found to be 1.474 g cm-3, 0.6421 cm3 g-1, 1.0021 cm3 g-1 and 0.3905. The results of density of gums and radius of gyration indicate that A. seyal molecules is more compact compared to A. senegal and A. polyacantha. Chemical potential range have been calculated from osmotic measurement for different concentration and was found to be -7.1739x10-2 to -6.9471x10-2, -13.8181x10-2 to -13.3817x10-2 and -23.1103x10-2 to -22.3804x10-2 joule g-1 for A. seyal, A. senegal and A. polyacantha respectively. Second virial coefficient, Free energy of mixing range and gums–solvent interaction parameter χ1 of A. seyal were found to be, 0.97x10-4, -0.475x10-2 to -0.833x10-2 joule g-1 and 0.4961 respectively. For A. senegal they were found to be, 1.85x10-4, -0.90911x10-2 to -1.6615x10-2 joule g-1 and 0.4928, while for A. polyacantha were found to be, 2.22x10-4, -1.4220x10-2 to -2.4786x10-2 joule g-1 and 0.4913. These results indicate that A. polyacantha gum thermodynamically resembles A. senegal gum and they interact with water more than A. seyal. The protein denaturation of A. seyal, A. senegal and A. polyacantha gums were studied using urea and guanidine hydrochloride, and it was found that urea was better denaturation agent than guanidine hydrochloride. The expansion factor of A. seyal, A. senegal and A. polyacantha was calculated from viscosity measurement in different solvents and was found to be 2.8, 5.8 and 3.2 respectivly.