Effect of air-drying on the generation of vitamin D₂ and 25-hydroxyvitamin D₂ by pulsed UV irradiation in button mushroom (Agaricus bisporus)

Fresh and dried mushrooms naturally generate vitamin D₂ when exposed to ultraviolet (UV) radiation. Vitamin D₂ and 25-hydroxyvitamin D₂ (25(OH)D₂) concentrations were compared in dried button mushrooms (Agaricus bisporus) exposed to pulsed UV radiation either before or after air-drying. A further aim was to assess the effect of air-drying on the generation of D vitamers. Fresh button mushrooms were irradiated (Irr) with a total of 200 mJ/cm² pulsed UV radiation before (Irr/AD) or after (AD/Irr) being air-dried (AD). A third group of fresh button mushrooms was irradiated but not air-dried (Irr). Control mushrooms were fresh and untreated. The D vitamers were quantified in freeze-dried samples using triple quadrupole mass spectrometry. Irr/AD mushrooms had more than double the concentration of vitamin D₂ than AD/Irr mushrooms (9.5 µg/g dry weight (dw) vs 4.6 µg/g dw). However, Irr mushrooms contained 6.3 µg/g dw. The concentration of 25(OH)D₂ in Irr mushrooms was 0.05 μg/g dw, while 0.14 μg/g dw was detected in Irr/AD mushrooms. There was no detectable 25(OH)D₂ in control mushrooms, nor in AD/Irr mushrooms. The sequence of irradiating and drying mushrooms was a key factor in generating vitamin D₂.