Conversion of xylan into value-added products

Sammanfattning: Today’s high demand on finding sustainable energy sources, replacing petroleum-based products and the needfor healthier food alternatives have forced us to search for natural recoverable resources and explore their manyhidden applications. One such resource is xylan, which has gained much attention as possible raw material forvarious exploitations. However, its wider industrial application puts demand on research achievements to reacha marketable product. The work throughout this thesis was focused on studying some of these applications withthe aim to improve the final product or its production process.Production of alkyl xylobioside and alkyl xylotrioside was achieved using a highly thermostable recombinantendoxylanase from Thermotoga neapolitana. This enzyme made it possible to directly react xylan with an alcoholto produce surfactant without the need for its hydrolysis to xylooligosaccharides (XOS). Furthermore, the effectof xylan concentration, enzyme dose, reaction water content, reaction temperature and initial pH on the yield ofthese surfactants was studied (Paper I).XOS as prebiotic, another remarkable product from xylan, was produced from wheat straw. Xylan was firstextracted with alkali and later hydrolysed to XOS using a variant of an alkali-tolerant endoxylanase from Bacillushalodurans S7. Its prebiotic properties were confirmed by growth of a putative probiotic strain; Lactobacillusbrevis DSM 1269 (Paper II). To further study this strain and understand how it utilizes the XOS we studied oneof its enzymes, a β-xylosidase from glycoside hydrolase family 43 (GH43). The kinetic studies using XOS ofdifferent chain length revealed that the enzyme displayed a higher catalytic efficiency for shorter chain lengthsubstrate, in line with data showing that XOS of short chain length can be taken up by L. brevis. Moreover, themolecular structure of this enzyme was solved using X ray crystallography showing a tetrameric structure, whichfurther assisted to better understand its catalytic activity in relation to its structure (Paper III).The potential application of xylan as film and coating was the driving force for our final study. For this purpose,arabinoxylan was mixed with tragacanth as a second polymer and cross-linked with malic acid. Based on theinitial type of arabinoxylan used, two types of films were produced with similar tensile strength and thermaldecomposition curves but significantly different elongation at break and swelling ratios. With further studies thesefilms have the potential to be used as edible films, wound dressing or drug coating (Paper IV).