Morphological, physico-chemical and structural characterization of gum kondagogu ( Cochlospermum gossypium): A tree gum from India

Abstract

Gum kondagogu ( Cochlospermum gossypium), a tree exudate gum is a plant growing naturally in the forests of India. This gum is yet to be commercially exploited, as the physico-chemical properties of this gum are yet to be characterized. Various physico-chemical methods like scanning electron microscopy (SEM), differential scanning calorimetry (DSC), static light scattering (SLS), viscometry, elemental analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction spectrometry (XRD), Fourier transform infrared spectroscopy (FT-IR), GC–MS, 1D( 1H and 13C) and 2D nuclear magnetic resonance (NMR) (double-quantum filtered correlated spectroscopy (DQF COSY), heteronuclear single-quantum coherence (HSQC) and heteronuclear multiple-bond coherence (HMBC)) have been employed to characterize this gum in the present study. SEM analysis suggests that the native gum has irregular particle size, while the deacetylated gum was found to be fibrilar. The weight-average molecular weight ( M w) of native and deacetylated gum was determined to be 8.5×10 6 and 2.5×10 7 g/mol, respectively, by SLS, while the intrinsic viscosity [ η] of native and deacetylated gum kondagogu was observed to be 32.68±0.23 and 59.34±dl/g, respectively. The glass transition temperature of the gum was observed to be 34.5 °C, by DSC. The XRD pattern of the native gum indicates a completely amorphous structure. Elemental analysis of the gum revealed the contents of carbon, hydrogen, nitrogen and sulfur to be 34.97, 5.58, 0.229 and 0.128 (w/w%), respectively. Gum kondagogu had high content of calcium, potassium and magnesium, and lower concentrations of aluminum, cadmium, cobalt, lead and nickel. The major functional groups identified from FT-IR spectrum include 3431/cm (–OH), 1731/cm (CH 3CO–), 1632/cm (–COO–), 1429/cm (–COO–) and 1249/cm (–CH 3CO). Analysis of acid-hydrolyzed gum by GC–MS, indicated the presence of rhamnose, galacturonic acid, glucuronic acid, β- d-galactopyranose, α- d-glucose, β- d-glucose, galactose, arabinose, mannose and fructose, while the 1D and 2D NMR, revealed the presence of the following sugar residues and their linkages—(1→2) β- d-Gal p, (1→6)- β- d-Gal p, (1→4) β- d-Glc p A, 4- O-Me- α- d-Glc p A, (1→2) α- l-Rha p and (1→4) α- d-Gal p A.