6 Wood Discoloration

9.5 Wood Saccharification and Sulphite Pulping 247
Fig.9.4. “Palo podrido” caused by Phlebia chrysocreas (a) andaChileancoweating“palo
podrido” (b) (photos J. Grinbergs)
1980). As a by-product, production of edible mushrooms may increase the
economy of fungal straw treatment.
9.5
Wood Saccharification and Sulphite Pulping
Both wood saccharification with acids and sulphite pulping may be termed
“chemical wood pretreatment” when the obtained sugars are subsequently
used for microbial or enzymatic conversions.
The acid wood saccharification yields monosaccharides from the wood carbohydrates.
Hydrolysis of lignocelluloses either with diluted or concentrated
acids has been practiced on a large commercial scale for many years. This technique
was used in the USA in the 1910s and in Germany and in Switzerland
during the Second World War. About 10 million m 3 of wood were saccharified
by acid hydrolysis with up to 48% sugar yield of the possible 70% yield in
the former Soviet Union around 1983 (Wienhaus and Fischer 1983). The main
product is glucose, which is the universal sugar for the majority of organisms.
Glucose can by either converted by yeasts, e.g., Candida utilis, aerobically
to fodder yeast (single cell protein, SCP; Dart and Betts 1991) or for human
feed, or glucose is anaerobically fermented to ethanol to be used as chemical
feedstock or as petrol substitution (Decker and Lindner 1979). Glucose fermentation
to ethanol was one of the first complex biological processes mastered by
man and became an important fuel and chemical feedstock in the mid-19th
century. However, with the rapid growth of the petroleum and petrochemical
industry following World War I, fermentation has been restricted primarily
to the brewing and distilling industries (Saddler and Gregg 1998). Ethanol
can be also obtained from xylose by the xylose-fermenting yeast Pachysolen
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