The effect of heat on the vitamin B6 of milk: I. Microbiological tests

Abstract

1. Four test organisms were used for the microbiological assay of vitamin B6. The test organisms and the forms of vitamin B6 active for them were: Saccharomyces carlsbergensis 4228 (pyridoxine, pyridoxamine and pyridoxal), Streptococcus faecalis R ATCC8043 and Str. faecium Ø51 (pyridoxamine and pyridoxal), and Lactobacillus casei ATCC7469 (pyridoxal).2. By simultaneous assay of the test material with the four organisms the amounts of pyridoxine, pyridoxamine and pyridoxal present were determined. The differential assay technique has been improved by the use of Str. faecium, which is more specific for measuring total pyridoxamine plus pyridoxal, instead of Str. faecalis.3. The optimum conditions for measuring vitamin B6 in milk were studied and the differential assay technique was applied in an investigation of the effect of heat on the vitamin B6 activity of milk.4. It was found that pyridoxal accounted for about 80% of the vitamin B6 activity of raw milk, the other 20% being due to pyridoxamine.5. In the manufacture of evaporated milk there was a marked fall in the pyridoxal and a slight increase in the pyridoxamine content. The overall loss was some 60%.6. On storage of evaporated and of sterilized liquid milk at room temperature there was a further loss of vitamin B6 activity. Most of the residual activity in stored evaporated milk appeared to be due to a substance other than pyridoxal or pyridoxamine, possibly pyridoxine.