Characterization of galactoglucomannan extracted from spruce (Picea abies) by heat-fractionation at different conditions

Water-soluble hemicelluloses were extracted from spruce chips by microwave heat-fractionation. The galactoglucomannan (GGM) extraction was evaluated on the basis of weight-average molecular weight (MW), yield and carbohydrate composition of the GGM. The MW was determined by size-exclusion chromatography with column calibration using off-line MALDI-MS analysis, and determination of mannan content in the fractions collected. Water impregnated spruce chips were heat-fractionated at three different temperatures (180, 190, and 200oC). The spruce chips were also impregnated in NaOH solutions of different concentrations, and then heat-fractionated at 190oC for 5min. The highest mannan yield (78% based on the amount in the raw material) was obtained from water impregnated spruce chips heat-fractionated at 190oC for 5min (MW of 3800). The highest MW (14,000) was obtained from impregnation with 2% NaOH (190oC, 5min), but the yield of mannan was very low (3%). Impregnation with 0.025% NaOH and heat-fractionation at 190oC for 5min resulted in extraction of GGM with MW of 9500 and a mannan yield of 31%. When the spruce chips were impregnated with =<0.05% NaOH an O-acetyl-galactoglucomannan was extracted, whereas when higher NaOH charges were used in the impregnation, the extracted GGM lacked acetyl groups. (Less)