Improvement of in vitro digestibility through biological treatment of water hyacinth biomass by two Pleurotus species

Biological delignification of lignocellulosic biomass of water hyacinth following fermentation by two Pleurotus spp., as well as suitability of using the highly digestible, protein-enriched, spent biomass as ruminant feed were investigated. Loss of organic matter was higher in all replicates inoculated with P. citrinopileatus than that with P. florida after all three degradation periods during both solid state fermentation (SSF) and under mushroom growing conditions, being at a maximum, 34.4 +/- 0.6% dry weight (d.w.) after third flush of mushrooms. Under both conditions, an extensive removal of hemicellulose during the initial growth period (22 d) and a delayed ligninolysis were observed. Loss of hemicellulose and cellulose was also higher (45.6 +/- 0.3% and 37.1 +/- 0.7% d.w., respectively, after the third flush) in biomass incubated with P. citrinopileatus than that with P. florida in all sets. Delignification was, however, higher (30.2 +/- 1.1% after third flush) by P. florida. The amount of reducing sugar present in the degraded biomass increased gradually during incubation and the highest value (3.1 +/- 0.4%) was obtained by P. citrinopileatus after 48 d under mushroom growing conditions. Crude protein of the bioconverted biomass increased up to 32 d in all replicates (maximum value 10.8 +/- 0.5% by P. florida in SSF), but decreased thereafter. Biological efficiency in terms of fruit body production was found to be higher in biomass incubated with P. florida (86.3%) than that with P. citrinopileatus (78.6%). Spent biomass enriched with mycelial protein of all replicates after 32 d, resulted improvement of dry matter digestibility, more so by P. florida (30.7 +/- 0.8%) than by P. citrinopileatus (27.1 +/- 0.5%) during SSF. The results showed that P. florida was more effective than P. citrinopileatus in delignification and is a biologically efficient species for production of highly digestible mycoprotein-rich ruminant feed. (C) 2003 Elsevier Ltd. All rights reserved.