Quantification of total vitamin B12 and identification of vitamin B12 compounds in commercial fermented tofu ( <i>furu</i> ) products

Vitamin B12 is primarily present in animal-derived foods and is scarce in plant-derived foods; therefore, vegetarians and vegans are at risk of deficiency. Although furu, a traditional Chinese fermented tofu product, has been reported to contain vitamin B12, it remains unclear whether the vitamin B12 compounds present are bioactive or inactive. In this study, the vitamin B12 content of eight commercial furu products was quantified using high-performance liquid chromatography. Gray furu showed the highest level (~1.1 μg/100 g), whereas the others contained < 0.4 μg/100 g. Liquid chromatography-tandem mass spectrometry revealed that only ~9% of the total vitamin B12 in gray furu was bioactive, with most identified as inactive corrinoids. Other products showed similar profiles. These findings indicate that commercial furu products are not reliable sources of vitamin B12, although gray furu may supply a modest amount of bioactive vitamin B12.