Vitamin B12 was determined and characterized in 19 dried Chlorella health supplements. Vitamin contents of dried Chlorella cells varied from <0.1 μg to approximately 415 μg per 100 g of dry weight. Subsequent liquid chromatography/electrospray ionization-tandem mass spectrometry analyses showed the presence of inactive corrinoid compounds, a cobalt-free corrinoid, and 5-methoxybenzimidazolyl cyanocobamide (factor IIIm) in four and three high vitamin B12-containing Chlorella tablets, respectively. In four Chlorella tablet types with high and moderate vitamin B12 contents, the coenzyme forms of vitamin B12 5'-deoxyadenosylcobalamin (approximately 32%) and methylcobalamin (approximately 8%) were considerably present, whereas the unnaturally occurring corrinoid cyanocobalamin was present at the lowest concentrations. The species Chlorella sorokiniana (formerly Chlorella pyrenoidosa) is commonly used in dietary supplements and did not show an absolute requirement of vitamin B12 for growth despite vitamin B12 uptake from the medium being observed. In further experiments, vitamin B12-dependent methylmalonyl-CoA mutase and methionine synthase activities were detected in cell homogenates. In particular, methionine synthase activity was significantly increased following the addition of vitamin B12 to the medium. These results suggest that vitamin B12 contents of Chlorella tablets reflect the presence of vitamin B12-generating organic ingredients in the medium or the concomitant growth of vitamin B12-synthesizing bacteria under open culture conditions.
Keywords: Chlorella sorokiniana; Chlorella tablets; vitamin B12.