Growth and bioconversion ability of oyster mushroom (Pleurotus ostreatus) on different agro-wastes

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The livestock industry in Ghana is challenged with high cost of quality feed ingredients. However, rice straw and groundnut shells are freely available in large quantities as agro wastes after rice and groundnuts have been harvested and processed. Though their use as animal feed is challenged with digestibility problems, through biotechnological means, these “wastes” could be turned into valuable animal feeds. This study pretreated and incubated rice straw (RS), groundnut shell (GS) and in equal proportions of rice straw and groundnut shell (RSGS) with Pleurotus ostreatus in a solid-state fermentation (SSF) for a period of five weeks. Proximate analysis, mineral composition, fibre fractions, anti-nutrients and in vitro dry matter digestibility were determined and compared. The fungus was able to improve the protein content significantly (P < 0.05) above the control samples, and protein enhancement was highest in RS (132.98%), whereas GS and RSGS recorded 65.41% and 61.43% respectively. The crude fibre component of the fermented samples also significantly reduced (P < 0.05) with GS recording a highest of 42.25%, followed closely by RSGS (39.69%) and RS (39.07%). The fungus also delignified the “wastes” with significant (P < 0.05) reduction in the lignin, cellulose and hemicellulose contents. Lignin for instance declined by 48.12% in RS, 36.39% in GS and 39.78% in RSGS. The mineral content (P, K and Ca) also significantly (P < 0.05) improved in the fermented samples as compared to the control. In vitro dry matter digestibility studies indicated that the samples were over 100% more digestible than the control at the end of the optimum fermentation period of the various substrates. The tannin levels in RS reduced by 76.9%, 75% in GS and 73.8% in RSGS. The study demonstrated that SSF of these agro wastes with P. ostreatus increased the level of limiting nutrients e.g. proteins and minerals while at the same time decreasing the fibre levels to enhance their digestibility for monogastrics and ruminants.
A thesis submitted to the Department of Biochemistry and Biotechnology in partial fulfilment of the requirements for the degree of Master of Biotechnology,