Vitamer-specific determination of vitamin B12 in food matrices: Analytical methodologies, challenges and future perspectives.

Vitamin B12 occurs in diverse food matrices, but reported concentrations often vary beyond expected biological differences because analytical workflows may quantify different measurands. This review integrates occurrence data from animal-derived, marine, fermented and plant-derived foods and critically evaluates methods ranging from microbiological and binding-based assays to HPLC, LC-MS/MS and stable isotope dilution. Particular attention is given to corrinoid analogue discrimination, cyanidation-induced measurand redefinition, native-vitamer instability, matrix effects, calibration strategies and vitamer-dependent cleanup. Recent cyanide-free UHPLC-MS/MS evidence shows that structural selectivity alone cannot compensate for inadequate control of extraction, photoconversion or form-dependent recovery. To improve transparency and inter-study comparability, we propose a three-level reporting framework based on explicit measurand definition, complete workflow description and vitamer-specific validation evidence.