Spatial-temporal distribution of oxygen and its effect on microbial dynamics and vitamin B12 content in lupin tempeh

Vitamin B12 is an essential vitamin for humans that can only be produced by some bacteria and archaea and is usually only found in animal (derived) products. In order to move from animal-based towards plant-based diets, supplementation of this vitamin is essential, especially for vegetarians and vegans. Tempeh is a popular meat replacer which has shown to be suitable for in situ vitamin B12 fortification. In this study, we analyzed the presence of fungal biomass, Propionibacterium freudenreichii, oxygen and vitamin B12 in lupin tempeh, produced by co-culturing Rhizopus microsporus var. oligosporus (Saito) CBS 338.62 and P. freudenreichii subsp. freudenreichii DSM 20271. We demonstrated that for all parameters mentioned above, spatial and temporal gradients exist within the solid state fermented matrix. These gradients occur inside the tempeh due to the interplay between the fungus, the bacterium and the lupin substrate during the course of fermentation. As fungal biomass increases, less oxygen is available due to the fast metabolism of the mold. When fungal metabolism slows down, enough oxygen can diffuse back into the tempeh which allows for P. freudenreichii to remain active and subsequently produce up to 20 μg vitamin B12 per 100 g of fresh lupin tempeh.