Effect and enzyme activity of Pleurotus ostreatus on cell wall of barley straw

A study was carried out to characterize exogenous fibrolytic enzymes obtained by solid fermentation (FS) of barley stubble inoculated with the fungus Pleurotus ostreatus (strain IE8) and its effect on barley stubble. The kinetics of enzyme (xylanases, cellulases and laccases) production was evaluated for 30 days; maximal cellulase activity (15.9 U/gss) was obtained after 8 days of fermentation, whereas for xylanases (80.5 U/gss) and laccases (3.46 U/gss) maximal titres were observed after 12 days, coinciding with the maximum concentration of extracellular protein (0.12 mg/gss). An enzymatic extract characterization was performed at controlled temperature (39°C) and two pH values (6 and 7). The enzymes showed greater stability at 39°C and pH 6, with values of residual activities of 77.5 %, 49.1% and 27.5 % for xylanases, cellulases and laccases, respectively, after 15 hours of incubation of the enzymatic extract under the conditions described above. Residual enzymatic activities at pH 7 were lower, with no significant differences among enzymes (cellulases: 36.8%; xylanases: 41.1% and laccases: 42.1%). Chemical analysis of the stubble after 30 days of fermentation revealed significant differences with the initial values, with decreases of 2.42%, 7.03% and 3.79% in the concentrations of neutral detergent fibre, hemicellulase and lignin, respectively. On the other hand, crude protein increased by 0.86%, and in vitro digestibility of dry matter changed from 39.6% to 42.3%. The present study shows the feasibility of using simple biotechnological processes, directly on barley stubble, in order to obtain fibrolytic enzymes which would increase dry matter digestibility in vitro, due to the destructuration of the fiber.