content between 70% and 80% on a wet basis. As the authors
explain the reason for the low conversion of ergosterol with a high
level of moisture may be due to the dilution effect of ergosterol at
very high moisture content. Table 3 presents data on moisture
level of UVB-irradiated dried mushrooms and the amount of ergosterol
in these products (before irradiation process). The higher content
of vitamin D2 especially in irradiated with UVB freeze-dried
fruit bodies of white button mushrooms compared with air-dried
may be due to the higher amount of ergosterol in the first ones
and in addition to the structure of the freeze-dried mushrooms.
Pei et al. (2014) presented a study on the impact effects of different
drying methods on the structure of dehydrated button mushroom
slices presented by scanning electron micrographs. Scientists claim
that the micrographs of the samples that were air-dried appeared
to have severe shrinkage, whereas freeze-dried products were relatively
large, with the internal pore structures. Such a pore structure
can facilitate the penetration of UVB radiation, and causes a
higher level of conversion of ergosterol in the freeze-dried fruit
bodies.
The obtained results that indicate the possibility of conversion
of ergosterol to ergocalciferol in processed fruit bodies of mushrooms
(dried by convection or freeze-drying method) provide an
opportunity to obtain new sources of vitamin D with its high content.
The fact that the enrichment in vitamin D may be performed
after the preservation process by drying greatly facilitates the
potential use of UV technology in the processing of mushrooms
in order to improve their nutritional value.
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