Effect of ultraviolet-A and ultraviolet-C light on the concentration of vitamin D2 and mechanical properties of Oyster mushrooms during growth

Abstract

The sun emits ultraviolet radiation in the form of ultraviolet-A (UV-A), ultraviolet-B (UV-B), and ultraviolet-C (UV-C) bands. Ultraviolet light has the potential to boost vitamin D2 production in mushrooms which are the only non-animal food source of vitamin D for humans. The ergosterol in mushrooms, a component of fungal cell membranes which serves the same function as cholesterol in animal cells, can be converted into vitamin D2 by exposure to controlled UV light. However, mushrooms grow in dark locations that receive inadequate sunlight to facilitate conversion of ergosterol to vitamin D2. The mechanical properties of the mushrooms produced after irradiation during growth is a very important factor to consider to meet consumers’ needs. This study investigated the effects of UV-A and UV-C light on both the concentration of vitamin D2 in oyster mushrooms during growth and the mechanical properties oyster mushrooms. Experiments were carried out with exposure of the mushrooms with UV-A (365nm) and UV-C (254nm) light during growth. The exposure time ranged from 10 minutes to 60 minutes at intervals of 10 minutes and irradiation was done for three days. Vitamin D2 concentration for UV-A and UV-C band was determined. The absorbance of vitamin D2 for UV-A light was 0.18 - 0.49 for 10 - 60 minutes of irradiation while for UV-C light the vitamin D2 content was 0.38 - 0.81 for 10 – 60 minutes of irradiation. On the other hand, the mechanical properties were investigated. The average storage modulus for UV-A and UV-C ranged from 7.614MPa and 6.850MPa for 10 minutes to 5.269MPa and 5.046MPa for 60 minutes exposure time respectively. The average loss modulus for UV-A and UV-C ranged from 1.779MPa to 0.5792MPa for 10 minutes exposure to 2.449MPa to 2.065MPa for 60 minutes exposure time respectively and the average loss factor for UV-A and UV-C ranged from 0.2771MPa and 0.1157MPa for 10 minutes to 0.3893MPa and 0.4450MPa for 60 minutes exposure time respectively. There was a significant difference between the storage modulus, loss modulus and loss factor of the irradiated samples by both UV bands with reference to the control sample, p ˂ 0.05. UV-C light irradiated samples had higher loss modulus and loss factor but low storage modulus as temperature increased from 35 - 100⁰C with respect to the control sample while UV-A light irradiated samples had lower loss modulus, low loss factor and higher storage modulus than UV-C irradiated samples. This study showed that oyster mushrooms with a well-defined content of vitamin D2 can be obtained with mechanical properties that do not affect the quality of the mushrooms.