Evaluation of the effect of of UVB radiation on vitamin D2 levels, antioxidant activity and microbial activity of white button mushrooms

Edible mushrooms consumption and cultivation as a food source has a long history and has attained great commercial importance. Mushrooms are eukaryotic organisms. There is chitin in the cell membrane of mushroom (Fungi) and they do not have the ability to photosynthesize. Edible mushrooms are important in terms of nutritional value among agricultural products around the world and in recent years the consumption of mushrooms has greatly increased. Edible mushrooms are rich in a variety of vitamins, proteins and soluble fats. They are also eaten as a main or a lateral food in raw or cooked form in a variety of appetizers, soups, stews, sandwiches and salads. Low calorie intake is good for those who want to lose weight. Mushrooms strengthen bones and are good for vitamin D deficiency. This vitamin is fat-soluble and comes in a variety of forms, including D1, D2 and D3. It is also known as sun vitamin, which is biologically active in animals and humans after sun exposure or UV radiation. Vitamin D deficiency causes rickets in children and osteoporosis in adults. Vitamin D consumption is associated with a significant reduction in the risk of breast cancer, colon cancer, prostate cancer, autoimmune diseases and cardiovascular disease. Some foods that are sources of vitamin D include: fish, cow liver, fish liver oil, cod and egg yolk. Moreover, some foods such as milk, cereals, some juices and processed cheese, yogurt, Margarine and ice cream can be fortified with vitamin D. Because many foods are low in vitamin D, many countries enrich foods with vitamin D in order to prevent osteoporosis. Enriching foods with vitamin D leads to more calcium availability in children, the elderly and women after menopause. As a result, vitamin D is important, and its deficiency is a major social problem. Mushrooms are known to be a good source of vitamin D. Mushrooms contains large amounts of ergosterol and pro-vitamin D2, which can be converted to vitamin D2 by UV rays. Vitamin D is an essential vitamin for people in communities. Mushrooms produce vitamin D2 in response to UV rays, which can be used as a valuable source of vitamin D2. In the present study, the effect of UVB irradiation on D2 levels, antioxidant activity and microbial population of white button mushroom was investigated.

white button mushroom in different forms (Whole mushroom, sliced mushroom and mushroom powder) and at different distances (4, 8 and 12 cm) from UVB irradiation source for 2 hours and then to measure the amount of vitamin D2 HPLC method is used. For scavenging activity, DPPH free radical method and for reducing power, Fe3+ ion method to measure antioxidant activity is used. Also PCA methods for total bacterial counting and DRBC for mold and yeast counting were employed.

According to the results, the amount of vitamin D2 was significantly increased in the treated mushrooms. The D2 level in the sliced mushroom with a thickness of 3 mm reached 94.37±6.66 g/g (701.10 % increase compared to control sample), which was more than other forms (sliced mushrooms with a thickness of 6 mm, whole mushroom and mushroom powder). This indicates the effect of the sample's contact surface with the irradiation source on the amount of produced vitamin D2. Also, the maximum amount of vitamin D2 at a distance of 4 cm 185.46 ± 5.41 g/g DM (1474.34% increase compared to the control sample) in the sliced sample (a thickness of 3 mm), this represents the importance of distance from irradiation source to quantity of the vitamin D2 production. Moreover, the effect of UVB irradiation on the antioxidant activity of white button mushrooms in different forms and at different distances from the irradiation source was also investigated. The results proved that UVB irradiation doesn't have significant effect on DPPH free radical scavenging activity. In the Fe3+ ion's reducing power the most effective distance was 4 cm (absorption: 1.68 ± 0.41) and also the mushroom powder had the highest absorption average (1.79 43 0.43) among other forms. Finally, by examining the effect of UVB irradiation on the microbial population of treated mushroom in different shapes and distances, it was found that UVB irradiation reduced the microbial population of the mushroom from 9.703 ± 0.16 log cfu/gr in the control sample to 5.36 log cfu/gr in the mushroom powder.

According to the results, UVB irradiation had a significant effect on vitamin D2 levels in all treatments. The effect of irradiation on vitamin D2 production decreased with increasing distance and the amount of vitamin D2 in Mushrooms were also decreased. Also, the surface of the samples to exposure to irradiation (mushroom thickness: 3 and 6 mm and the shape of the fungus: whole mushrooms, fungal slides or fungal powder) was effective in the amount of vitamin D2 produced in the samples, so that the amount of vitamin D2 was increased in the treated forms by increasing the contact area of the sample with the irradiation source (3 mm thick sliced mushroom> 6 mm thick sliced mushroom> whole mushroom> mushroom powder). The result of the UVB irradiation effects on the antioxidant activity of the white button mushroom revealed that the level of scavenging activity of DPPH radical decreased by reducing distance from the irradiation source. However, the effect of irradiation on the reducing power had opposite effect, the reducing power decreased with increasing distance, however, did not have a significant effect on antioxidant activity of mushrooms. Due to the antimicrobial properties of UV radiation, the microbial population of mushrooms treated with UVB irradiation was decreased and this effect decreases with increasing distance from the radiation source. According to researches, the levels of vitamin D2 produced in edible mushrooms exposed to UVB irradiation are very available to the body and it can provide the body's need of this vitamin. According to the obtained results of the present study, it can be concluded that the treatment of white button mushrooms with UVB rays to enrich it via increasing the amount of vitamin D2 is a fast, safe and accessible way.