Studies on the biomass production of Pleurotus ostreatus using peat extract as substrate

Manu-Tawiah, Wireko (1988) Studies on the biomass production of Pleurotus ostreatus using peat extract as substrate. Masters thesis, Memorial University of Newfoundland.

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Abstract

Pleurotus ostreatus mushroom mycelium was grown in submerged culture with acid extract from peat as a basic substrate. The proximate chemical composition of the peat extract was determined. The total reducing sugars constituted about 50% of the total carbohydrate (TCH) concentration. The total nitrogen content was low at about 0.6 g/L of the pet extract. The total ash was about 4.5%, of which 1.2% was P₂O₅ and 0.87% K₂O. -- Different concentrations of water-diluted peat extract were tested in shake flask experiments in an attempt to overcome the effect of growth inhibitors apparently present in non-diluted peat extracts. The best results were obtained with a ratio of one part peat extract diluted with one part water. Several operating variables were studied to optimize the growth of the mycelial biomass of P. ostreatus. The best results produced approximately 5 g/L of dry biomass with a yield of 60% and an efficiency of 33%. The results were obtained in 192 hours at an inoculum ratio of 5.0% (v/v), and incubation temperature of 28 ± 1°C, an initial pH of 5.0 ± 0.1 and an agitation speed of 150 rpm. The addition of 1.5% glucose to the diluted peat extract medium increased the growth to approximately 14 g/L of dry biomass with a yield of 70% and an efficiency of 45%, indicating that the diluted peat extract was deficient in carbon. -- The nutritional requirements of the P. ostreatus mycelium grown in peat extract were studied to enhance the growth of the mycelial biomass. The fungus grew better on hexose sugars (glucose and mannose) than on pentose sugars (xylose and arabinose) and required additional nitrogen, phosphorus and potassium for growth. Growth was also better on organic sources of nitrogen than on ammonium salts of inorganic acids. The addition of 5.0 g/L yeast extract and 4.0 g/L KH₂PO₄ to the peat extract media produced approximately 7 g/L dry biomass with a yield of 73% and an efficiency of 46%. -- Agitation and aeration were optimized and the dissolved oxygen concentration was monitored in a 2 Liter fermenter to study the growth of the P. ostreatus mycelium biomass in the peat extract. The best results produced approximately 9 g/L of biomass with a yield of 72% and a productivity of 70 mg/L/hour. These results were obtained in 96 hours at an agitation speed of 200 rpm, an aeration rate of 1.0 vvm, an inoculum ratio of 5.0% (v/v), an incubation temperature of 28 ± 1°C and a pH of 5.0 ± 0.1. Higher agitation speeds and aeration rates produced lower growth and a dispersed mycelial growth form. The morphology of the P. ostreatus growth form was also affected by the pH and the media composition. -- The chemical composition of the P. ostreatus mycelium biomass was analyzed and compared with that of the fruiting body produced on solid peat to study the nutritional quality of the product. The mycelium contained approximately 40% crude protein, 8% ash, which contained K, P, Ca and Mg as major minerals, 36% TCH, 6% fiber and 3% total fat. The protein contained 17 amino acids, including all the essential amino acids, and was high in threonine, lysine, tryptophane, arginine, leucine and phenyalanine, but was deficient in methionine when compared with egg protein. Three essential fatty acids (palmitic, oleic and linoleic acids) were identified in the biomass.

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