Statistical Optimization of Ultraviolet Irradiate Conditions for Vitamin D(2) Synthesis in Oyster Mushrooms (Pleurotus ostreatus) Using Response Surface Methodology

Response surface methodology (RSM) was used to determine the optimum vitamin D(2) synthesis conditions in oyster mushrooms (Pleurotus ostreatus). Ultraviolet B (UV-B) was selected as the most efficient irradiation source for the preliminary experiment, in addition to the levels of three independent variables, which included ambient temperature (25–45°C), exposure time (40–120 min), and irradiation intensity (0.6–1.2 W/m(2)). The statistical analysis indicated that, for the range which was studied, irradiation intensity was the most critical factor that affected vitamin D(2) synthesis in oyster mushrooms. Under optimal conditions (ambient temperature of 28.16°C, UV-B intensity of 1.14 W/m(2), and exposure time of 94.28 min), the experimental vitamin D(2) content of 239.67 µg/g (dry weight) was in very good agreement with the predicted value of 245.49 µg/g, which verified the practicability of this strategy. Compared to fresh mushrooms, the lyophilized mushroom powder can synthesize remarkably higher level of vitamin D(2) (498.10 µg/g) within much shorter UV-B exposure time (10 min), and thus should receive attention from the food processing industry.