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 B₁₂c-lactone] that is inactive in humans. Given that shiitake mushroom lacks the ability to synthesize vitamin B₁₂ de novo, the vitamin B₁₂ found in dried shiitake fruiting bodies must have been derived from the bed logs.