Vitamin B12 Biofortification of Plant‐Based Foods Through Fermentation With Propionibacterium freudenreichii : Mechanisms, Challenges, and Opportunities

ABSTRACT

Vitamin B12 (VB12) is essential for human health but occurs predominantly in animal‐derived foods, posing a challenge for adequate intake on plant‐based diets. Fermentation with Propionibacterium freudenreichii offers a route to in situ fortification, in which the vitamin is generated within the food matrix rather than added as a purified fortificant, eliminating the separation and purification steps required for industrial production. This review examines the mechanistic and technological basis of that approach. It sets out the chemical and physiological requirements any dietary VB12 source must satisfy, and the analytical consequence that follows: microbiological assays cannot distinguish bioactive cobalamin from inactive analogs, so reported concentrations in fermented plant foods require confirmation by chromatographic or mass‐spectrometric methods. It then summarizes VB12 biosynthesis in P. freudenreichii , the factors governing its production, and applications across cereals, legumes, side‐streams and other plant matrices. Substrate composition, particularly cobalt availability and pH‐buffering capacity, together with oxygen supply and the choice of cofermenting strains, largely determines yield. Recent fungal–bacterial cofermentations have reached concentrations exceeding earlier plant‐based fermentations by more than an order of magnitude, indicating that nutritionally sufficient concentrations are attainable. Digestive release rather than synthesis now appears the more consequential constraint: in vitro bioaccessibility is high in processed products but substantially lower in unprocessed fermented material, pointing to cell disruption during processing as the determining step. Scale‐up beyond pilot demonstrations and economic competitiveness remain unresolved, and no controlled human trial has yet evaluated the bioavailability of in situ synthesized VB12—the decisive step before any nutritional claim can be made.