Influence of purification on physicochemical and emulsifying properties of tamarind (Tamarindus indica L.) seed gum

The effects of different purification methods on the yield, chemical composition, physicochemical, and emulsifying properties of tamarind seed gum were investigated. Low purity gum (TSGLP) was extracted from whole tamarind seeds; medium purity gum (TSGMP) was extracted from defatted tamarind kernel, and high purity gum (TSGHP) was extracted as TSGMP and soluble protein was removed. Fourier transform infrared spectra showed that characteristic peaks of the polysaccharide backbone did not change through purification, while deconvolution of the amide I region revealed that the protein was denatured. Hydrophobic interaction chromatography of TSGHP showed a main fraction (F3) containing protein strongly attached to the polysaccharide backbone. Yield and zeta (ζ)-potential values of the gums decreased as their purification increased. Flow behavior of TSG solutions (1.5 and 2.0% w/w) was described by Ellis model, where low shear limiting viscosity and time constant associated to the relaxation time of polymers in solution exhibited higher values as concentration and purification were increased. Oil-in-water (O/W) emulsions (E) prepared with 2% w/w TSG gum solutions showed initial oil droplets of 1.35 ± 0.15 μm for ELP, of 4.82 ± 0.10 μm for EMP, and of 9.45 ± 0.10 μm for EHP. ELP and EHP exhibited higher creaming stability (21 days) than EMP. It was concluded that emulsion stability was due to a complex interplay between several factors, including chemical composition, apparent viscosity, contact angle, interfacial tension dynamics, surface charge, all of which had bearing on the electrosteric repulsion terms and adsorbed layer mechanical properties around the oil droplets.