Evaluation of Antioxidant and Iron Chelating Activities of A Wild Edible Oyster Mushroom Pleurotus Cystidiosus from Tanzania

Abstract

This study was conducted in order to assess the levels, activities and establish the influence of postharvest storage methods on antioxidants of the giant wild edible mushroom Pleurotus cystidiosus. Standard analytical methods were employed to determine the level and activities of antioxidants. It was followed by comparing the results in order to establish the influence of postharvest storage methods namely heat drying, freezing, sun drying, refrigeration, salt drenching and dehydration using silica gel beads. The mushroom caps and stipes were treated separately. Results showed that irrespective of the preservation method and portion of the mushroom used, P. cystidiosus exhibited very high values of the number of antiradical activity units in 1 mg of extract (EAU₅₁₅), ranging from EAU₅₁₅ 3.25 to 17.00. The mushroom also portrayed very high 1,1-diphenyl–2picryhydrazyl (DPPH) free radical scavenging ability recorded at very low concentrations of crude extracts (0.0125 to 0.800 mg/ml) and the EC₅₀ values ranging from 0.035 to 0.150 mg/ml. Likewise the highest ferrous iron chelating ability of 98.3% was recorded at a low concentration of 0.80 mg/ml. With respect to the antioxidant activities in relation to the fruiting body portions, there were consistently higher antioxidant levels and antioxidant activities in the cap portion than in the stipe of the mushroom. Preservation method also influenced the antioxidants activities whereby the highest radical scavenging and iron chelating activities were found in the oven dried, silica gel dried and refrigerated mushrooms while, salt drenched mushrooms performed the least. These results suggest that P. cystidiosus contain antioxidant levels and activities which are useful properties for a valuable food source of nutraceutics potential; however, salt drenching method of preservation should be avoided. This giant mushroom is recorded for the first time in the country thus, isolation of its germplasm for spawn production, and subsequent domestication remains to be investigated.

Keywords: Antiradical scavenging, iron chelating, antioxidant, wild  Pleurotus cystidiosus