Physicochemical Properties of Tamarind (Tamarindus indica) Seed Polysaccharides

The polysaccharides of two samples of Tamarindus indica (Tamarind) seed; namely Light brown (LB) and Dark brown (DB), were extracted and studied for their physicochemical and functional properties. The physiochemical properties were determined and compared to those of commercial pectin to investigate their potentials as probable substitute of pectin. The two polysaccharide extracts were similar in most of the physical properties such as solubility in hot water, pH, and refractive indices as compared to commercial pectin. The intrinsic viscosity, molecular weights and equivalent weights were similar in both extracts and higher than that of commercial pectin. The polysaccharides were the major components in the extract comprising 88.85%, 85.21% and 92.43% for LB, DB and commercial pectin, respectively. The tamarind seed polysaccharides form gels over a wide pH range in the presence of sucrose with or without acid and base, while commercial pectin forms gels over a narrow range (acidic) in the presence of sucrose. Although the protein levels in the polysaccharides were higher compared to commercial pectin, their gel formatting ability was found more applicable as compared to commercial pectin. This indicated that the protein level did not interfere with gel formation. The functional properties of both extracts, as a gelling agent, indicated that polysaccharides of both samples contained residual amount of uronic acid, no galacturonic acid, no acetyl group, small amount of methoxyl group, and high degree of estrification. The commercial pectin, however, contained a high level of uronic acid and relatively low degree of estrification. The high performance liquid chromatography showed that the two polysaccharide extracts contain pentose sugars (xylose and arabinose) and hexose sugars (glucose and galactose). The molar ratios of these sugars were 2:1:3:1 in both extracts. Commercial pectin contains similar sugars but with fructose instead of xylose.