SEPARATION AND QUANTITATIVE-DETERMINATION OF B12 VITAMERS IN DAIRY-PRODUCTS BY AN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY RADIOASSAY METHOD

Vitamin B-12 and the four vitamers of B-12: cyanocobalamin (CNCbl), hy droxocobalamin (OHCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) have been determined in milk and dairy products by means of a n high performance liquid chromatography-radioassay method. This metho d allows the detection of picogram levels of each vitamers. Average re covery of vitamer standards is 0.953. For dairy products, total vitami n B-12 are 2.2 nmol/l for fresh milk, 1.8 nmol/l for pasteurized milk, 1.4 nmol/l for sterilized milk and 1.74 nmol/l for milk reconstituted from dry power milk. Vitamers presents varie from 0.17 to 0.6 nmol/l for OHCbl, 0.20 to 0.72 nmol/l for CNCbl, 0.31 to 1.08 nmol/l for AdoC bl and 0.26 to 0.31 nmol/l for MeCbl. This indicates the conversion be tween vitamers or their thermal destruction during extraction.