Structural characterization and thermal behavior of a gum extracted from Ferula assa foetida L.

The gum asafoetida, an oleo-gum-resin from root of Ferula assa foetida, was extracted through alcoholic procedure followed by water extraction and then biochemically characterized using colorimetric assays, Fourier infrared spectroscopy, gas chromatography coupled to mass spectrometry, and 1D and 2D nuclear magnetic resonance. The gum was mainly composed of carbohydrates (67.39% w/w) with a monosaccharide distribution of 11.5: 5.9: 2.3: 1 between Gal, Ara, Rha and GlcA (molar ratio) and proteins (arabinogalactan protein). The polysaccharide consisted of a (1 -> 3)-beta-D-galactan backbone ramified predominantly from O-6 but also from O-4 and O-4,6. Side chains included terminal-alpha-L-Araf, terminal-alpha-L-Rhap, (1 -> 3)-alpha-L-Araf, (1 -> 5)-alpha-L-Araf, terminal-beta-D-Galp, beta-D-GlcA and traces of (1 -> 4)-beta-D-GlcA. X-ray diffraction pattern showed a semi crystalline microstructure. Thermal behavior of the gum was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed temperatures below and upper 200 degrees C as dominant regions of weight loss.