Impact on Vitamin D2, Vitamin D4 and Agaritine in Agaricus bisporus Mushrooms after Artificial and Natural Solar UV Light Exposure

Commercial mushroom production can expose mushrooms post-harvest to UV light for purposes of vitamin D-2 enrichment by converting the naturally occurring provitamin D-2 (ergosterol). The objectives of the present study were to artificially simulate solar UV-B doses occurring naturally in Central Europe and to investigate vitamin D-2 and vitamin D-4 production in sliced Agaricus bisporus (button mushrooms) and to analyse and compare the agaritine content of naturally and artificially UV-irradiated mushrooms. Agaritine was measured for safety aspects even though there is no rationale for a link between UV light exposure and agaritine content. The artificial UV-B dose of 0.53 J/cm(2) raised the vitamin D-2 content to significantly (P < 0.001) higher levels of 67.1 +/- 9.9 mu g/g dry weight (DW) than sun exposure (3.9 +/- 0.8 mu g/g dry DW). We observed a positive correlation between vitamin D-4 and vitamin D-2 production (r(2) = 0.96, P < 0.001) after artificial UV irradiation, with vitamin D-4 levels ranging from 0 to 20.9 mu g/g DW. The agaritine content varied widely but remained within normal ranges in all samples. Irrespective of the irradiation source, agaritine dropped dramatically in conjunction with all UV-B doses both artificial and natural solar, probably due to its known instability. The biological action of vitamin D from UV-exposed mushrooms reflects the activity of these two major vitamin D analogues (D-2, D-4). Vitamin D-4 should be analysed and agaritine disregarded in future studies of UV-exposed mushrooms.