Degradation of rice straw by Pleurotus flabellatus.

Degradative changes in the constituents of rice straw substrate during the
growth and commercialproduction of fruit bodies by Pleurotus flabellatus
were investigated. There was a continuous increase in the free sugars from
the time of inoculation until the end of harvesting of the fruit bodies,
whereas the free amino acids reached a maximum at the end of mycelial
growth and showed a slight decrease after fructification. Glucose, xylose,
arabinose, cellobiose and a higher oligosaccharide represented the
spectrum of sugars produced. Of the 12 amino acids (apart from two
peptides) identified, aspartic acid, histidine and tyrosine were the major
components, Solubilities and spectral characteristics of lignin degraded in
the straw substrate were studied using alkali-extracted lignin. Laccase and
protease activities in the straw substrate at different stages of fungal
‘degradation could be correlated to the decreases in the staw lignin and
protein contents, respectively. Colour reactions of the fungus on several
phenolic media, demonstration of phenolic oxidases in the straw substrate,
and ability of the fungus to degrade lignin conclusively proved that the
fungus under study is a typical ‘white rot’ fungus. Degradation of the straw
substrate by the fungus reached a maximum at the end of harvest of the fruit
bodies. The spent straw substrate (left over after harvesting the fruit bodies)
contained free sugars and amino acids, respectively 5 and 2 times the
concentration of those in the undegraded straw substrate, and lignin
decreased to about 25% of the level in the straw before fermentation.
Potential applications of the spent straw substrate as an upgraded form of
rumen feed and for the production of single-cell protein are discussed.