B Vitamins bioavailability in plant-based foods: Beyond content to nutritional impact

B vitamins are essential water-soluble cofactors involved in metabolic regulation and neurological function. In plant-based diets, maintaining adequate B vitamin status is challenging because nutritional value depends not only on vitamin content but also on bioavailability. Although many plant foods contain substantial quantities of B vitamins, their absorption is generally lower than that from animal-derived sources due to differences in chemical form, matrix associations, and conjugation state. Thiamine and niacin often require liberation from bound forms; folates must undergo enzymatic deconjugation; vitamin B6 frequently occurs in glycosylated forms with reduced biological activity; and vitamin B12 is absent from unfortified plant foods. Bioavailability is further modulated by dietary composition, gastrointestinal conditions, and host genetic variability. Assessment approaches, such as in vitro models, cellular transport systems, and in vivo biomarkers, provide complementary but incomplete perspectives on physiological availability. Fermentation has emerged as a promising strategy to enhance B vitamin bioavailability in plant foods through microbial synthesis, matrix modification, and reduction of antinutritional factors. Applications in cereals, legumes, vegetables, and fruits demonstrate substantial improvements in vitamin content and accessibility. This chapter emphasizes the disconnect between analytical vitamin content and physiological impact and positions fermentation as a scalable approach to optimize B-vitamin nutrition in plant-based dietary patterns.