Hemicelluloses from Agricultural and Forestry Crops Isolation, Characterisation, and Enzymatic Hydrolysis

Sammanfattning: Hemicelluloses are tremendous sources of renewable raw materials, which utilisation have the potential to be highly increased in the future. Hemicelluloses are among the major groups of compounds in plant cell walls, together with cellulose and lignin. These three components are closely associated, making them difficult to separate from each other. Hemicelluloses are complex polysaccharides and two major classes are heteroxylans and heteromannans. In this work, the extraction, isolation, characterisation, modification and enzymatic hydrolysis of hemicelluloses from agricultural and forestry crops have been investigated. Extraction of the hemicelluloses arabinoxylan from barley husks, and corn fibres and acetylated galactoglucomannan (AcGGM) from spruce chips, was performed with heat treatment at neutral conditions, using microwave irradiation or steam pretreatment. Extraction of polymeric hemicelluloses was possible and the hemicelluloses extracted from all species investigated were acetylated. Isolation and concentration of the soluble hemicelluloses were performed with membrane filtration and size-exclusion chromatography (SEC), respectively. Glycosyl hydrolases are important tools for the characterisation and modification of the properties and structure of hemicelluloses. The influence of side group substitution on AcGGM solubility was investigated using an a-galactosidase and chemical de-acetylation with alkali. B-mannanase catalysed hydrolysis of AcGGM with various degrees of natural and chemical substituents revealed steric hindrance and decreased hydrolysis rate with increased substitution. Hydrogels were made from chemically modified AcGGM. BSA was incorporated as a model drug. The release of BSA from AcGGM hydrolgels was increased by the addition of b-mannanase. The affinity of a mannan-binding module to galactomannan was demonstrated in an aqueous two-phase system. A potential method for primary recovery of enzymes with the aid of a carbohydrate-binding module is suggested. In conclusion, methods of extracting hemicelluloses are presented together with further isolation with membrane filtration, characterisation with SEC and enzymatic hydrolysis. Finally, an example of the utilisation of hemicelluloses is provided by creating hydrogels. This work has gained insight into the chemistry of hemicelluloses and suggestions for future applications aimed at a more sustainable society.