Optimisation of solid substrate fermentation of wheat straw into animal feed by Pleurotus ostreatus: a pilot effort

Abstract

The solid substrate fermentation (SSF) of wheat straw with the selected white-rot fungus, Pleurotus ostreatus, was optimised for its cultural and nutritional conditions and substrate pretreatment based on selective delignification (more lignin than holocellulose degradation), crude protein content and in vitro dry matter digestibility (IVDMD). The differences between treatments were found to be statistically significant ( P ⩽ 0.01). The fungus behaved optimally under the following set of fermentation conditions: initial pH, 5.5; initial moisture, 55%; temperature, 22 °C; period, 21 days; form of inoculum-grain culture (spawn); substrate turning frequency, once at mid-incubation; urea (nitrogen source) level, 1% (sterile) or 2% (unsterile); single superphosphate (phosphorus + sulphur source), 0.3%; no addition of free carbohydrates (as whey or molasses). A maximum (10.4%) increase in IVDMD accompanied by a 2.7% (g per 100 g dry matter of original straw) degradation of lignin was attained in the optimised SSF under the above conditions. The digestibility could, however, be further improved by using a two-stage process involving pretreatment (physical/chemical/biological) before fermentation. For practical farm applications, urea treatment and ensiling to be the most feasible pretreatments. The laboratory scale (40-g lots) optimised SSF was also scaled-up to 4 kg (cooked and uncooked) and 50 kg (uncooked) fermentations.