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Fluorometric Determination of Vitamin A in Dairy Products

Research Laboratories, Health Protection Branch, Department of National Health and Welfare, Ottawa, Canada

ABSTRACT

A rapid method has been devised for the determination of vitamin A (retinol) in milk, artificially fortified milk, butter, cheese and ice cream. Samples (1 ml or 1 g) were saponified and extracted with petroleum ether in stoppered centrifuge tubes. Retinol content of extracts was measured fluorometrically, Chromatography of the unsaponifiable lipids on columns of alumina and hydroxyalkoxypropyl Sephadex demonstrated that retinol was responsible for almost all of the measured fluorescence. Retinol amounts are reported for Canadian whole milk, 2% fat-milk and fortified 2% fat-milk. Samples were obtained monthly between March and November 1971. Mean retinol (µg/100 ml±se) in whole milk was low in March (28.3±3.0) and November (32.1±1.5) and maximal in September (45.8±2.3). A similar cycle was observed in the values for 2% fat-milk which invariably were approximately two-thirds those of whole milk. Sixteen out of 18 fortified milks met their label claims but two had only 19 and 22 µg retinol/100 ml.