Surface morphology, chemical and structural assignment of gum Kondagogu (Cochlospermum gossypium DC.): An exudate tree gum of India

Indian forests are a major source of large number of non-wood forest products. One such product is an exudate tree gum, regionally called as gum Kondagogu (Cochlospermum gossypium DC.), belonging to the family Bixaceae. This gum is collected by tribals in the state of Andhra Pradesh and marketed by Girijan Cooperative Society, Andhra Pradesh, India. Experimental work carried out in our laboratory on this gum has resulted in assigning a separate identity to this gum as compared to the well established and commercially exploited gum Karaya. Gum kondagogu has unique physiochemical properties as compared to other tree gums. Proximate analysis of the gum indicates that it has high volatile acidity and waterbinding capacity. Elemental composition of gum kondagogu was determined by Energy dispersive X-ray fluorescence spectrometry (EDXRF). Surface morphological studies based on SEM analysis showed irregular shape with sharp edges in the native gum, while the deacetylated gum showed a fibrilar and porous structure. AFM analysis indicated that native gum was visualized as spherical lumps, suggesting an interor intra-molecular aggregation. TEM image of native gum kondagogu showed that the polymer was an extending linear chain with branch points. FT-IR spectrum of native gum indicated the predominant presence of acetyl group (12%w/w). Analytical data on gum kondagogu indicated that the major neutral sugars were arabinose, mannose, α-D-glucose, β-D-glucose, rhamnose and galactose, whereas uronic acids (D-Glucuronic acid, β-Dgalacturonic acid and α-D-galacturonic acid) were the major acidic sugars. Structural assignment was carried out using acid hydrolysis, Smith degradation and NMR studies [H, C, 2-D NMR (TOCSY and NOESY)]. Smith degradation analysis indicated that the back bone structure of gum kondagogu was that of α-D-GalpA-(1→4)-α-L-Rhap and can be grouped under rhamnogalacturonan type of gum. The experimental work provides enough evidence to exploit this natural biopolymer in food, textile and pharmaceutical industry.