Determination of optimal extraction time and temperature by response surface methodology to obtain high-level antioxidant activity in culinary-medicinal oyster mushroom, Pleurotus ostreatus (Jacq.:Fr.) P. Kumm. (higher basidiomycetes)

A central composite design of response surface methodology (RSM) was employed to optimize the extraction time (X1: 266.4-393.6 min) and temperature (X2: 42.9-57.1°C) of Pleurotus ostreatus aqueous extract with high antioxidant activities, namely DPPH radical-scavenging activity, ABTS radical cation inhibition, and ferric reducing/antioxidant power, as well as total phenolic content (TPC). Results showed that the data were adequately fitted into four second-order polynomial models developed by RSM. The extraction time and temperature were found to have significant quadratic effects on antioxidant activities and TPC. The optimal extraction time and temperature were 282.3 min and 42.9°C (DPPH), 393.6 min and 42.9°C (ABTS), 340.4 min and 49.8°C (FRAP), and 347.6 min, 49.7°C (TPC), with corresponding yields of 53.32%, 73.20%, 37.14 mM Fe2+ equivalents/100 g, and 826.33 mg gallic acid equivalents/100 g, respectively. These experimental data were close to their predicted values. The establishment of such a model provides a good experimental basis for employing RSM to optimize the extraction time and temperature for high antioxidant activities from P. ostreatus.