Abstract
An unknown vitamin D compound was observed in the HPLC-UV chromatogram of edible mushrooms in the course of analyzing vitamin D2 as part of a food composition study and confirmed by liquid chromatography-mass spectrometry to be vitamin D4 (22-dihydroergocalciferol). Vitamin D4 was quantified by HPLC with UV detection, with vitamin [3H] itamin D3 as an internal standard. White button, crimini, portabella, enoki, shiitake, maitake, oyster, morel, chanterelle, and UV-treated portabella mushrooms were analyzed, as four composites each of a total of 71 samples from U.S. retail suppliers and producers. Vitamin D4 was present (>0.1 µg/100 g) in a total of 18 composites and in at least one composite of each mushroom type except white button. The level was highest in samples with known UV exposure: vitamin D enhanced portabella, and maitake mushrooms from one supplier (0.2–7.0 and 22.5–35.4 µg/100 g, respectively). Other mushrooms had detectable vitamin D4 in some but not all samples. In one composite of oyster mushrooms the vitamin D4 content was more than twice that of D2 (6.29 vs. 2.59 µg/100 g). Vitamin D4 exceeded 2 µg/100 g in the morel and chanterelle mushroom samples that contained D4, but was undetectable in two morel samples. The vitamin D4 precursor 22,23-dihydroergosterol was found in all composites (4.49–16.5 mg/100 g). Vitamin D4 should be expected to occur in mushrooms exposed to UV light, such as commercially produced vitamin D enhanced products, wild grown mushrooms or other mushrooms receiving incidental exposure. Because vitamin D4 coeluted with D3 in the routine HPLC analysis of vitamin D2 and an alternate mobile phase was necessary for resolution, researchers analyzing vitamin D2 in mushrooms and using D3 as an internal standard should verify that the system will resolve vitamins D3 and D4.
Highlights
Vitamin D is a 9,10-secosteroid and 6 forms have been identified [1]
Identification of vitamin D unknown in mushrooms Initially the unknown vitamin D form observed in a variety of mushrooms in previous work [14] was thought to be vitamin D3, because it eluted at the same retention time as a vitamin D3 standard chromatographed under the conditions that were being used for analysis of vitamin D2 and displayed the characteristic UV chromophore
The unknown was hypothesized to be vitamin D4 (22-dihydroergocalciferol) because it co-eluted with an authentic vitamin D4 using the alternative solvent system and because its precursor is present in mushrooms
Summary
Vitamin D is a 9,10-secosteroid and 6 forms have been identified [1]. Vitamin D2 (9,10-seco(5Z,7E)-5,7,10(19),22-ergostatetraene-3b-ol; ergocalciferol) and vitamin D3 (9,10-seco(5Z,7E)5,7,10(19)cholestatriene-3b-ol; cholecalciferol) are the predominant forms of vitamin D relevant to human nutrition. Vitamin D3 originates from animal sources, and vitamin D2 is derived predominantly from fungi, such as yeast [2,3]. A primary source of vitamin D3 in humans and many animals occurs from the conversion of 7-dehydrocholesterol in the epidermis to vitamin D3 during exposure to ultraviolet (UV) radiation present in sunlight [2]. Fish and fish liver oils are naturally rich dietary sources of vitamin D3. Other foods in the U.S marketplace are fortified (typically with vitamin D3), including milk, cheeses, yogurts, cereals, margarines, and orange juice
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