Separation of polymeric galactoglucomannans from hot-water extract of spruce wood

Two methods for separation of polymeric galactoglucomannans (GGMs) from a hot-water extract of spruce wood, i.e., membrane filtration and precipitation in ethanol–water, were compared. Filtration through a series of membranes with different pore sizes separated GGMs of different molar masses, from polymers to oligomers. Only polysaccharides were precipitated in ethanol–water. With the optimal water content of 5–15%, the precipitated amount was about 6% on wood basis. The average molar mass of the precipitated polysaccharides was 10–12 kDa with a molar mass range of 4–20 kDa. GGMs comprised about 80% of the precipitated hemicelluloses. Other precipitated polysaccharides were mainly arabinoglucuronoxylans and pectins (rhamnogalacturonans). Analysis of a lignin-free, ethanol-precipitated GGM preparation by 13C NMR spectroscopy verified that it was structurally almost identical with a GGM-rich ethanol precipitate obtained from spruce wood by extraction at much milder conditions, 90 °C for 60 min.