The hemicellulose extract from Cynara cardunculus: a source of value-added biomolecules produced by xylanolytic thermozymes

The Cynara cardunculus hemicellulose fraction was recovered from its stem and leaf biomass and converted into valuable molecules by exploiting the extracellular xylanase and beta-xylosidase activities produced by the thermophilic bacterium Geobacillus thermantarcticus. Several degradation procedures for the arabinoglucuronoxylan extract were proposed by using efficient and different enzymatic preparations, containing both or only one xylanolytic activity of G. thermantarcticus. In particular, when the xylanase and beta-xylosidase activities were used separately in hydrolysis reactions, xyloglucurono-oligosaccharides or xylose were obtained with a yield of 32% and 62.6% respectively, with reference to the hemicellulosic extract. Furthermore, the synergic action of beta-xylosidase/xylanase activities was exploited in transglycosylation processes for the production of xylo-conjugated compounds; xylosides of primary alcohols with increasing carbon chains and aromatic alcohols were produced starting from the C. cardunculus hemicellulose, which was selected as a cheap donor. When 2-phenoxyethanol was selected as an acceptor, 2-phenoxyethyl beta-xyloside, xylobioside and xylotrioside were prepared with a yield of 38.5% with respect to the hemicellulosic extract and spectroscopically characterized.