Isolation, characterization and enzymatic modification of water soluble xylans from Eucalyptus grandis wood and sugarcane bagasse

BACKGROUND: There is growing interest in utilizing xylans as biodegradable polymers to replace synthetic additives, coatings and encapsulation matrices. However, techniques are required to reduce the water solubility of the xylan for such applications. The study objective was to isolate and characterize water soluble xylans from Eucalyptus grandis wood and sugarcane (Saccharum officinarum L) bagasse for subsequent precipitation in water by enzymatic modification. RESULTS: The water soluble xylans were extracted from E. grandis and bagasse using two mild alkali-low-temperature extraction methods in which the xylan was recovered either by ultra-purification (Hoije) or ethanol precipitation (Lopez). Yields of 66 and 35% were obtained for the xylan extracted from bagasse and E. grandis, respectively, using the Hoije method and 28 and 12%, respectively, using the Lopez method. The xylans were hydrolysed by selective removal of arabinose and 4-O-methylglucuronic acid (4-O-MeGlcA) side chains by treatment with alpha-L-arabinofuranosidase and alpha-D-glucuronidase, respectively. The alpha-L-arabinofuranosidase removed about 14% of the available arabinose in the xylans extracted from bagasse using the Hoije method, which led to precipitation in water. However, the alpha-D-glucuronidase removed only 2% 4-O-MeGlcA of the available 4-O-MeGlcA from the xylans extracted from bagasse and E. grandis using both the Hoije and Lopez methods, and failed to show visible precipitation of the xylan in water. CONCLUSION: The xylans extracted from bagasse suited the substrate specificities of the alpha-L-arabinofuranosidase for side chain removal and precipitation in water. However, the dosage of alpha-D-glucuronidase for precipitating the xylan would need to be increased. Copyright (c) 2012 Society of Chemical Industry