Influence of gaseous phase, light and substrate pretreatment on fruit-body formation, lignin degradation and in vitro digestibility of wheat straw fermented with Pleurotus spp.

Wheat straw was fermented in the solid state with Pleurotus sajor-caju and P. eryngii at 25°C under different concentrations of oxygen and carbon dioxide. Lower than 20% oxygen in the gaseous phase adversely affected the loss of organic matter, the lignin degradation and the change in straw digestibility with both species of Pleurotus. Higher concentrations (10%–30%) of carbon dioxide, with 20% oxygen in the atmosphere, slightly decreased the loss of lignin and organic matter when compared with the losses under oxygen or air. In spite of better lignin degradation by P. sajor-caju, the process efficiency with P. eryngii was higher, because of lower loss of organic matter during the fermentation. Fruit-bodies were not formed by P. eryngii during the period of experiment in any of the treatments.

In P. sajor-caju, fruit-bodies were only formed either in flasks closed with cotton plugs or supplied with continuous flow of sterile air. Carbon dioxide inhibited the process of primordia initiation and fruit-body development. A short exposure (20 min day⁻¹) to light was essential for primordia and fruit-body formation. The substrate changes and process efficiency with respect to increase in digestibility were much higher in darkness than in light. Light leads to intensive fruit-body production and a different pattern of substrate degradation. The indigenous microflora of wheat straw inhibited fruit-body formation and caused a higher organic matter loss, accompanied by a decrease in digestibility of the fermented wheat straw.