Conifers, hemicelluloses

The availability of both the cellulose and hemicellulose in untreated wood sawdust is low and for conifers such as lodgepole pine, eastern hemlock, and balsam fir is essentially zero. 

Conventionally, woody trees were broadly classified as softwood or gymnosperm and hardwood or angiosperm. Hardwood comes from angiosperms, such as oak, eucalyptus, and alder, which are dicots (Octave and Thomas, 2009). Softwood usually comes from evergreen conifer trees like pine or spruce. Other classifications of forest-based plants are broad-leaved trees and pine-leaved trees. Almost 46% of biorefinery prefers raw materials from conifer species, mainly spruce, pine, etc., and 31% of broad-leaves such as eucalyptus. Mostly stem wood is preferred as a suitable feedstock for the biorefinery process. Approximately 8% of the known biorefinery processes utilize all parts of the tree (Fitzpatrick et al., 2010). Thus the consensus in the biorefinery industry is that the feedstock selection should be based on the main constituents of the wood (cellulose, hemicellulose, and lignin) and not on specific chemicals (glucose, xylose, etc.) generally considered in conventional fermentation processes. 

Hemicelluloses from many woods, particularly conifers (softwoods) contain glucomannoglycans which may be isolated by fractionation procedures. The glucomannoglycan from western red cedar [Thuja plicata Donn) is a typical example. It contains D-glucose and D-mannose only, in the ratio 2 5, and is a short-chain, essentially linear, /S-d-(i - 4)-linked polymer. Similar glucomannoglycans have been isolated from western hemlock [Tsuga heterophylla), sitka spruce (Picea sitchensis) and other softwoods. Glucomannoglycans from Norwegian spruce (Picea aHes) are a-D-(i - 4)-Unked. 

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