Isolation and characterization of galactoglucomannan from spruce (Picea abies)

Water-soluble hemicelluloses were extracted from spruce chips by microwave heat fractionation. The chips were impregnated with water at different pH values. Screening of heat-fractionation conditions, i.e. impregnation medium, temperature and residence time was performed with the aim to extract O-acetyl-galactoglucomannan. The impregnation and heat fractionation conditions were evaluated on the basis of the yield of dissolved mannan (oligo- and polysaccharides), molecular weight of the carbohydrates and amount of dissolved lignin. Increasing temperature and residence time increases the yield of mannan and decreases the molecular weight of dissolved carbohydrates. For a structural study of the extracted carbohydrates the chips were impregnated with water and treated at 200oC for 2min. Oligo- and polysaccharides were fractionated with preparative size-exclusion chromatography from the filtered extract.The structure of the obtained saccharides in two fractions 8 and 9 was determined by 1H NMR spectroscopy. The polysaccharides in the fractions were O-acetyl-galactoglucomannan with a degree of polymerization ~20 and ~11 for fractions 8 and 9, respectively. The molar ratio for galactose:glucose:mannose was approximately 0.1:1:4. About one-third of the d-mannosyl units are substituted by O-acetyl groups almost equally distributed between C-2 and C-3.