Analysis of Lactulose Preparations by Spectrophotometric and High Performance Liquid Chromatographic Methods

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Abstract
Spectrophotometric methods of analysis were applied to sugar mixtures produced during isomerization of lactose to lactulose. A combination of 4 established spectrophotometric methods was used to quantitate galactose, tagatose, lactose and lactulose, the 4 major sugars present. A method originally developed for determining lactose with methylamine at 65.degree. C and pH 12.7 was suitable for combined measurement of lactose and lactulose. After a specific determination of lactose with .beta.-galactosidase and glucose oxidase, lactulose was measured by difference. A high pressure liquid chromatographic separation of galactose, tagatose, lactose and lactulose was achieved on a commercial carbohydrate analysis column with a mixture of water and acetonitrile used as eluent. Analysis of lactulose syrups by the new high pressure liquid chromatographic method yielded results that agreed with those by the spectrophotometric methods and required much less time.