A new enzymatic spectrophotometric assay for the determination of lactulose in milk

A new enzymatic spectrophotometric assay for the determination of lactulose in milk samples was developed. This method entailed the use of beta-galact osidase which hydrolyses lactulose giving fructose and galactose, and fruct ose dehydrogenase which reacts with fructose in presence of a tetrazolium s alt (MTT), giving a coloured compound which can be detected spectrophotomet rically at 570 nm. The assay showed a lactulose detection limit in milk of about 10 mg l(-1), a linear range of 20 divided by 800 mg l(-1) and a relative standard deviat ion of 5%. The correlation with the determination of lactulose in milk usin g reference procedures was good. Moreover this procedure was found suitable for the quantitation of lactulose in milk after the heat treatment process , and more convenient for the rapid and sensitive estimation of lactulose i f compared with previous published enzymatic methods. (C) 2000 Elsevier Sci ence B.V. All rights reserved.