Gum ghatti contains a soluble gum and an insoluble gel which partially dissolves on boiling. Maceration of the gel in watex gives a perfectly stable dispersion which for practical purposes behaves as a solution. The viscosity of the gel dispersion is ca 10-30 times that of the soluble gum. The proportion of gel in four commercial batches of gum ghatti varied from 8 to 23%. The viscosity of the whole gum dispersion depends largely on the proportion of gel. The viscosity of gum ghatti can be closely controlled by blending to a fixed proportion of gel.
Some physical properties of aqueous solutions of African Albizia zygia (D.C.) Macbride have been evaluated. Approximately 80 % of the gum is soluble in the cold with the remainder dispersed as fine particles of gel. pH titration of the gum indicates one acid group, pK, = 3.8, for every three monosaccharide units. Solutions of the gum exhibit typical polyelectrolyte behaviour. The viscosity of the solutions increases with concentration but above 1.5 % the solutions exhibit shear-thinning. The viscosity of an ice cream mix containing the gum and the properties of the resultant ice cream are compared with standard mixes.
Gum ghatti may be readily separated into a water-soluble fraction and a gel fraction. Although the gel fraction contains a higher proportion of calcium ions this is not the cause of gel formation since electrolytes which displace calcium ions do not dissolve the gel. Single-salt forms of the gel fraction have very similar properties. Added simple electrolytes produce no specific effects related to calcium ion concentration. Different cations have different affinities for the available anionic sites in the gel and this is apparently the reason for the higher calcium concentration in the gel fraction. The gel structure is destroyed by sodium borohydride which suggests that it results from intermolecular linkages unrelated to the cation.
Potentiometric titration of gum karaya was used to determine the acid equivalent weight and the proportions of the acid groups in the salt form and the free acid form. Alkaline hydrolysis was used to determine the acyl groups attached to the gum. These determinations were also carried out with other tree-exudate gums including gum arabic, gum jeol (Lannea coromandelica gum) and tree-gums from Sterculia tragacantha, Acacia sieberana, Acacia polyacantha and Albizia zygia. Potentiometric titration also showed the presence of basic groups attached to the polyanion in some gums. The variation of viscosity with pH can be correlated with the potentiometric titration curve.
Cold water extraction of gum ghatti gives a soluble gum and an insoluble gel. The two fractions were shown by potentiometric titration to have the same acid equivalent weight and to be largely in the salt form, with less than 10% in the free acid form. Quantitative analysis of the two fractions for metal ion content showed that the gel fraction was largely a calcium salt. The soluble fraction contains calcium, potassium, sodium, and magnesium. Precipitation of the calcium ions reduces the viscosity but the original viscosity is not restored by addition of calcium ions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.