3.3. Production of vitamin D2 by sliced fresh button mushrooms
Fig. 1 presents data on the content of vitamin D2 in sliced fresh button mushroom subjected to UVB irradiation for a period of 5–30 min. In addition for comparison, whole mushrooms with gills facing (closed fruit bodies) were irradiated with UVB for 30 min. It can be seen from the data in Fig. 1 that the prolonged irradiation with UVB does not increase ergocalciferol content in fresh button mushrooms. During the exposure vitamin D2 content rapidly increased and reached a maximum level of 74.2 μg/g dw within 15 min, then considerably decreased to level of 34.4 μg/g dw after 30 min of UVB irradiation. The data shows that the sliced mushrooms contained more vitamin D2 (34.4 μg/g dw) compared to the whole mushrooms (11.4 μg/g dw) after 30 min of UVB irradiation. This may be due to the fact that the distribution of precursor of vitamin D2 (ergosterol) within mushrooms tissue is different and the highest concentration of previtamin D2 was found in gills compared to stalks and caps (Jasinghe & Perera, 2005). In the sliced mushrooms the gills were directly exposed to UVB irradiation differently than in the whole fruit bodies. The average moisture content of fresh button mushrooms used in this study was found to be around 92%