Synthesis and physio-chemical properties of sulphated tamarind (Tamarindus indica L.) seed polysaccharide

Tamarind seed polysaccharide (TSP) is a galactoxyloglucan isolated from seed kernel of Tamarindus indica. TSP has already been used in the industrial fields, due to its physical, chemical, and biological properties (Shukla et al., 2018). It is a neutral and water-soluble polysaccharide; nonetheless, its high viscosity makes solubilization time consuming and feasible at low concentrations. Also, the absence of charges on the chain does not allow electrostatic interactions with charged biological or chemical molecules. For this reason, in this study we conducted a chemical modification of the polysaccharide adding sulphated groups on the TSP chain. The presence of negatively charged groups may allow a better solubilization of the polysaccharide and also specific binding to proteins or receptors, giving new biological properties to TSP (Wang et al., 2018) . The sulfation reaction of TSP was performed in one-step process, using dimethylformamide as a solvent, and sulfur trioxide pyridine complex as reagent. Characterization of the chemical-physical properties of the sulfated products are conducted through different analytical approaches to verify the successful synthesis. Studies of viscosity, morphology, chemical structure, and molecular weight distribution are performed to obtain the complete characterization of the synthesized products. The substitution degree is obtained by potentiometric titration, and the distribution of sulphated groups on the sugars chain is studied by NMR spectroscopy and mass spectrometry; specifically, the hydrolyzed sulfated TSP sample obtained by enzymatic degradation with cellulase and xyloglucanase were investigated. Sulphated TSP products have a molecular weight in the range of 400 kDa-1000 kDa compared to TSP which have a molecular weight of 600 kDa, a substitution degree on the repetitive unit of TSP in the range of 5-50% of the 21 hydroxyl groups that can be sulphated, exhibit lower viscosity than TSP and show higher solubility than pristine TSP.