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Effect of Microwave-Convective Drying on Antioxidant Activity and Color of Oyster Mushroom (Pleurotus ostreatus)

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131619707,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Mrittika Bhattacharya, Prem Prakash Srivastav, Hari Niwas Mishra
Keywords:   Ergothioneine Pleurotus ostreatus Microwave-convective dryer DPPH radical scavenging activity Total phenolics.

Abstract. Ergothioneine, a potent antioxidant, has been found in highest concentration in oyster mushroom (Pleurotus ostreatus). The purpose of the present study was to optimize the drying air temperature and residual moisture content (w.b.) for the maximization of ergothioneine content, total phenolic content (TPC), 2,2-diphenyl-1-picryhydrazyl (DPPH) radical scavenging activity, total reductive power activity (potassium ferricyanide) and colour using response surface methodology (RSM). Oyster mushrooms were dried in microwave-convective dryer, the temperature range was varied from 60 to 80 °C and residual moisture content (w.b.) was varied from 5 to 20%, each at 5 levels. A rotatable central composite design consisting of 13 experimental runs with five replicates at the central points were applied and second-order polynomial models were used to describe the experimental data regarding the responses. Ergothioneine content was found to be highest at 70 °C and 12.5% residual moisture content (wb). Total phenolic content was found to decrease with increase in temperature, 11.8 to 4.6 mg GAE/gm dw. IC50 for DPPH and total reductive power activity showed gradual increase, showing decline in the antioxidant activity with rise in temperature, 9.9 to 0.1 mg/ml and 0.0033 to 0.0012 mg/ml respectively. Color change of the samples was observed to be affected by rise in drying temperature and residual moisture content (wb), as it caused darkening. Thus, the optimized values of responses can be obtained at drying temperature of 69°C and 9% (wb) residual moisture content, yielding an ergothioneine content of 1.7 mg/gm dw, total polyphenols of 8.9 mg GAE/gm dw, IC50 for DPPH activity of 0.09 mg/ml, IC50* for total reductive power assay 0.0027 mg/ml and colour of the samples having ΔE of 18.

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