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

Eastern Regional Research Center³, Philadelphia, PA 19118

ABSTRACT

Spectrophotometric methods of analysis were applied to sugar mixtures produced during isomerization of lactose to lactulose. A combination of four established spectrophotometric methods was used to quantitate galactose, tagatose, lactose, and lactulose, the four major sugars present. In addition, a method originally developed for determining lactose with methylamine at 65°C and pH 12.7 was suitable for combined measurement of lactose and lactulose. After a specific determination of lactose with ß-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.

¹ Southern Regional Research Center, Agricultural Research, Science and Education Administration, US Department of Agriculture, New Orleans, LA 70179.

² Postdoctoral Fellow supported by Dairy Research Foundation.

² Agricultural Research, Science and Education Administration, US Department of Agriculture.