2.3. Irradiation of freeze- and hot-air dried mushrooms
The fresh sliced mushrooms (3–4 mm) were frozen at −20 °C for 24 h and then lyophilized in a freeze dryer (Christ Alpha 1–2 LD plus, Germany) for 72 h. The condenser temperature was set at −60 °C, the vacuum was maintained at 0.8 mbar, and the shelf temperature was set at 25 °C. The second part of fresh sliced mushrooms (3–4 mm) were subjected to hot-air drying in the same manner as described in Section 2.2. Within 12 h after the completion of the drying process, the dried mushrooms were subjected to UVB irradiation. Hot-air and freeze-dried sliced mushrooms (about 20 g) were spread single-layered on a cleaned area of crate (28 × 38 cm) and then treated with UVB for 5–30 min and at the same conditions as described in Section 2.2. The lamp delivered a target UVB dose from 69 mJ/cm2 to 411 mJ/cm2, depending on the exposure time (5–30 min.). Next samples were subjected to extraction and analysis of vitamin D2 and ergosterol.