Characterization of vitamin B12 compounds in the fruiting bodies of shiitake mushroom (Lentinula edodes) and bed logs after fruiting of the mushroom

This study determined the vitamin B12 content in commercially available dried fruiting bodies of shiitake mushroom, Lentinula edodes. The vitamin B12 contents in dried donko-type fruiting bodies with closed caps (5.61 ± 3.90 μg/100 g dry weight), did not significantly differ from those of dried koushin-type fruiting bodies with open caps (4.23 ± 2.42 μg/100 g dry weight). The bed logs after fruiting of the mushroom also contained the vitamin B12 levels similar to that in the dried shiitake fruiting bodies. To determine whether the dried shiitake fruiting bodies and their bed logs contained vitamin B12 or other corrinoid compounds that are inactive in humans, we purified corrinoid compounds using an immunoaffinity column and identified vitamin B12 using vitamin B12-dependent Escherichia coli 215 bioautograms and liquid chromatography-electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) chromatograms. Dried shiitake fruiting bodies rarely contained an unnatural corrinoid vitamin B12[c-lactone] that is inactive in humans. Given that shiitake mushroom lacks the ability to synthesize vitamin B12de novo, the vitamin B12 found in dried shiitake fruiting bodies must have been derived from the bed logs.