King tuber mushroom (Pleurotus tuber-regium (Fries) Singer) is found in the continents of Africa, Asia and Australia. It is a macro-fungus with edible sclerotium, used both as food and herbal medicine. It grows naturally on decaying wood in the forest. When cultivated, it provides good source of income to farmers. It aids in transforming agricultural wastes to biomass due to its ability to grow on them. It is usually kept by local farmers and traders for long duration under ambient temperature during post-harvest storage. This research aimed at determining the effect of post-harvest storage at ambient temperature for long duration on the nutritional constituents, amino acid profile, antioxidant activity and biologically active constituents profile of the king tuber mushroom in order to ascertain the best time for its use as food or herbal medicine. Nutritional and medicinal properties of the sclerotia of the mushroom were analyzed when freshly harvested, at 8 and 16 weeks of post-harvest storage at ambient temperature. The nutritional constituents of the mushroom were determined by proximate analysis, employing the Standard Methods of Association of Official Analytical Chemists (AOAC), while the amino acid profile was determined by gas chromatography – flame ionization detector (GC-FID) technique. In vitro antioxidant activity was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay, hydrogen peroxide scavenging assay ferric reducing antioxidant potential (FRAP) assay and by monitoring the degree of lipid peroxidation. Gas chromatography – mass spectrophotometric (GC-MS) technique was employed for the identification of compounds with nutritional and medicinal properties present in the mushroom. Results show that the best time to use the mushroom as food is when it is freshly harvested; however it can be used as herbal medicine after long post-harvest storage.
Keywords: GC-MS profile, King tuber mushroom, Pleurotus tuber-regium, in vitro antioxidant activity, nutritional constituents, post-harvest storage
