Effects of Microwave Heating on the Loss of Vitamin B(12) in Foods.

To clarify the effects of microwave heating on the loss of vitamin B-12 in foods, raw beef, pork, and milk were treated by microwave heating and then their vitamin B-12 contents were determined according to a chemiluminescent vitamin B-12 assay with hog intrinsic factor. Appreciable loss (similar to 30-40%) of vitamin B-12 occurred in the foods during microwave heating due to the degradation of vitamin B-12 molecule by microwave heating. When hydroxo vitamin B-12, which predominates in foods, was treated by microwave heating and then analyzed by silica gel 60 thin layer chromatography, two vitamin B-12 degradation products were found. One of the compounds with a R-f of 0.16 was purified and partially characterized. The vitamin B-12 degradation product did not show any biological activity in the growth of a vitamin B-12 requiring microorganism, Euglena gracilis Z, and was not bound to hog intrinsic factor, a mammalian vitamin B-12 binding protein. Intravenous administration of the compound (1 mu g/day) for 7 days to rats showed that the compound neither has toxicity nor acts as a vitamin B-12 antagonist in mammals. These results indicate that the conversion of vitamin B-12 to the inactive vitamin B-12 degradation products occurs in foods during microwave heating.