Morphological, physico-chemical and structural characterization of gum kondagogu (Cochlospermum gossypium): A tree gum from India
Introduction
Gum kondagogu (Cochlospermum gossypium) belongs to Cochlospermum spp. and family Bixaceae. Even though gum karaya (Sterculia urens), also known as Indian tragacanth, and gum kondagogu are classified in the same group, there are considerable differences in their physico-chemical properties (Janaki & Sashidhar, 1998; Kumbhare & Bhargava, 1999). Natural gums are obtained as exudates from different tree species, which exhibit unique and diverse physico-chemical properties and have a wide variety of applications (Verbeken, Dierchx, & Dewettinck, 2003). Commercially important tree gums include gum arabic, gum karaya and gum tragacanth (Phillips & Williams, 2001). Earlier, the natural plant exudate gums were classified into various groups depending on the basic chain structure and structural units that contribute to the polymeric form of the gum (Aspinall, 1967). Contemporarily, the tree gums are grouped into (i) type II arabinogalactans (AGs, e.g. gum arabic), (ii) substituted glucuronomannans (e.g. gum ghatti) or (iii) substituted rhamnogalacturonans (e.g. gum karaya) (Sims & Furneaux, 2003), based on the nature of polysaccharide type. Interestingly, gum tragacanth has a mixture of type II AG and galacturonan-type polysaccharides (Stephen & Churms, 1995). The physico-chemical and structural characterization of many other higher exudate gums, such as Combretum (Anderson & Weiping, 1990), Hakea (Eagles, Stephen, & Churms, 1993), Enterolobium (León de Pinto, Martínez, De Corredor, Rivas, & Ocando, 1994), Prospis (Goycoolea, Calderon de la Barca, Balderrama, & Valenzuela, 1997), Acacia tortuosa (León de Pinto, Martínez, Mila de Bolano, Rivas, & Ocando, 1998) Anacardium (De Paula, Heatley, & Budd, 1998), Anacardium (Menestrina, Iacomini, Jones, & Gorin, 1998), Spondias (León de Pinto et al., 2000), Pithecellobium (León de Pinto, Martínez, Ocando, & Rivas, 2001) and Albizia (De Paula, Santana, & Rodrigues, 2001), Acacia glomerosa (León de Pinto, Martínez, & Sanabria, 2001), Sterculia apetala (Marvelys, Martínez, Sanabria, León de Pinto, & Julio, 2006) have been reported in the contemporary literature. The chemical composition of gum samples obtained from different Sterculia species and sourced from different geographical regions were found to be quite similar (Anderson, McNab, Anderson, Braown, & Pringuer, 1982). These tree gums are polysaccharides containing hexuronic acids in salt forms, with a number of neutral monosaccharides that are often esterified in highly branched structures (Roberts, Zhong, Prodolliet, & Gooddall, 1998). Characterization and rheological properties of Sterculia striata gum in comparison with S. urens (Karaya) gum has also been investigated (Brito, Silva, De Paula, & Feitosa, 2004). Gum kondagogu, gum karaya and gum tragacanth have higher viscosity and lower solubility. They swell in water, absorbing a large amount of water and produce gel or show thixotropic viscosity behavior. Gum karaya is a complex of partially acetylated polysaccharide obtained as a calcium and magnesium salt and has a branched structure with a high molecular mass of ∼16×106 Da (Le Cerf, Irinei, & Muller, 1990). Gum tragacanth and gum obtained from Enterolobium cyclocarpum have complex, highly branched, heterogeneous nature, having high uronic acid content and show high intrinsic viscosity (Anderson & Grant, 1988; Oliveira, Silva, De Paula, Feitosa, & Paula, 2001). Very few studies were carried out to characterize gum kondagogu (Fig. 1), which is available as a forest produce from the states of Andhra Pradesh, Madhya Pradesh and Rajasthan of India. Due to lack of morphological, structural and detailed physico-chemical information on this gum, gum kondagogu has not been commercially exploited, in the field of pharmaceutical, cosmetic, paper, textile and other industries. Earlier, toxicological evaluation of gum kondagogu was carried out so as to enable its use as a food additive (Janaki & Sashidhar, 2000). An understanding of the physico-chemical properties and structural characterization of gum kondagogu is essential in exploiting its potential as a food additive and for other industrial applications.
In the present paper, we report morphological, physico-chemical and structural aspects of gum kondagogu in order to provide a separate identity to this tree gum. The methods employed for the analysis include (i) scanning electron microscopy (SEM), (ii) static light scattering (SLS) and dilute solution viscosity, (iii) differential scanning calorimetry (DSC), (iv) elemental analysis (carbon (C), hydrogen (H), nitrogen (N) and sulfur (S)), (v) mineral analysis by inductively coupled plasma atomic emission spectrometry (ICP-AES), (vi) X-ray diffraction spectrometry (XRD), (vii) Fourier transform infrared spectroscopy (FT-IR), (viii) GC–MS analysis and (ix) 1D and 2D nuclear magnetic resonance (NMR).
Section snippets
Materials
Gum kondagogu samples (Fig. 1) were collected from Girijan Co-operative Corporation, Hyderabad, a Government of Andhra Pradesh undertaking, Hyderabad, India, and gratis samples were provides by m/s D.K. Enterprises, Hyderabad, India. Gum kondagogu (grade-1, hand picked, fresh, clean with no extraneous material) was used in the experimental analysis. Gum samples collected were stored in airtight polypropylene jars in desiccated condition. De-ionized (Milli-Q) water was used for all experiments.
Results and discussion
Scanning electron microphotographs of native and deacetylated gum are shown in Fig. 2, Fig. 3, at 500× magnification and 50 μm scale. The microphotographs of gum provide the surface morphology of the gum in two forms (native and deacetylated). It is clear from the Fig. 2 that the native form of the gum has irregular particle size. Deacetylated gum was found to be fibrilar (Fig. 3), indicating the loss in particulate morphology that was observed in the native form of the gum, suggesting that
Conclusion
Morphological, physico-chemical and structural characterization of gum kondagogu provides further insight into the potentiality of this tree gum among the other tree exudate gums reported in contemporary literature. Even though both gum karaya and gum kondagogu are classified under the same group, there are significant differences in their properties pertaining to intrinsic viscosity, mineral and elemental composition, sugar composition, weight-averaged molecular weight and Mark–Houwink's
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