Extraction, isolation and characterization of inulin from Agave sisalana boles

Agave sisalana Perrine is a widespread species of the Brazilian Northeast region, where it is exploited only as a source of hard fiber (sisal). Although some other Agave species are sources of fructans, there is no study on this issue on A. sisalana. This paper aimed at extracting and isolating inulin from aqueous extract of A. sisalana boles. After preparation of extracts, crude inulin was precipitated with acetone at low temperature (4 degrees C). After purification by ion-exchange chromatography, a white powder was obtained by freeze-drying and characterized by X-Ray Diffraction (XRD), thermal analysis, Circular Dichroism (CD) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS). Moreover, its polysaccharide structure was confirmed by Fourier Transformed Infrared (FT-IR) spectroscopy and Nuclear Magnetic Resonance (NMR). FT-IR analysis pointed out absorption at 1420 cm(-1), corresponding to deformation of CH2-OH lying on fructose ring, while absorption at 1075 cm(-1) was assigned to C-O and C-C stretching vibrations of inulin pyranose ring. NMR showed the presence of one signal in the anomeric region at 8 5.4 ppm and others between 3.1 and 4.2 ppm in the H-1 spectrum, besides a chemical shift at 104.4 ppm corresponding to the anomeric region of the C-13 spectrum of an internal beta-fructofuranose unit. XRD highlighted the amorphous state of inulin-rich powder, thermal analysis a glass transition temperature in the range between 50.0 and 55.8 degrees C, CD a good thermal stability, and MALDI-TOF-MS a prevalence of oligosaccharides with degree of polymerization in the range 5-13. These techniques revealed that A. sisalana boles contain inulin with features similar to those extracted from other commercial sources such as Agave tequilana or Agave atrovirens, which extends the economic importance of this species beyond its simple use as a fiber source.