Spruce glucomannan: Preparation, structural characteristics and basic film forming ability

In this study one representative hemicellulose in spruce wood, low galactosyl substituted glucomannan (GM), has been prepared and purified from holocellulose by NaOH/H3BO4 extraction, Fehling reagent precipitation and HCl regeneration. The GM structure obtained was comprehensively characterized by FTIR, hydrolysis-IC, SEC, and various solution- and solid state NMR spectroscopies. In addition, two pretreatment methods have been evaluated to form films from the GM. It was found that the spruce GM is composed of galactose, glucose and mannose in a ratio of 0.03:1:3.4. The molecular masses are around 255 kDa (Mw) against pullulan standards. The GM was almost free from other polysaccharides such as xylan (0.61%) and free from metal ions (<0.2% ash content). After blending with glycerol or pre-acetylation, two yellowish transparent films have been obtained after solution casting. For the former, water affinity was observed while for the latter water resistance was noticed. Potential high value applications of this GM include packaging and coatings in food and pharmaceutical industry.