Requirement of Biotin
The biotin requirement of microorganisms is well established. In animals there is no practical method now of establishing the quantitative need for this vitamin, since large amounts of it are supplied through intestinal bacterial synthesis. In some of the earlier balance studies in man it was found that the urinary excretion of biotin often exceeded the dietary intake, and the fecal excretion was greater than the intake in every case. At any rate, daily needs appear to be met by diets containing 150-300 Ilg of the vitamin.
Determination of Biotin
The assay of biotin is complicated by the presence in natural materials of biotin analogues, ~ome of which may have varying degrees of biotin activity or even antibiotin activity for some of the test organisms used. Animal assays have largely been replaced by microbiological procedures. Some materials, such as urine and milk, may be assayed without previous hydrolysis, but in many substances the combined biotin must be released by acid hydrolysis. Glick and others presented an extremely sensitive method for biotin using L. arabinosus.
