Validation of Enzytec™ Liquid Combi Lactose/D-Galactose for Enzymatic Determination of Lactose and D-Galactose in Selected Foods: Official Method 2024.10 First Action

Abstract Background Lactose is a disaccharide composed of D-galactose and D-glucose. Lactose composes 2–8% of milk by weight. Lactose is digested in the small intestine by the enzyme lactase. Lactase deficiency can lead to lactose intolerance in adults. Objective Enzytec™ Liquid Combi Lactose/D-Galactose is an enzymatic test kit for the determination of lactose and D-galactose in milk, milk products, infant formula, chocolate, sausage meat, almond milk, salad dressing, bread and cookies. Excluded are lactose-free dairy products that have been enzymatically treated with lactase. Methods The kit contains two sets of reagents in a ready-to-use format and is suitable for automation. Lactose is cleaved with ß-galactosidase. Resulting D-galactose is oxidized by a galactose-dehydrogenase and NAD+. The amount of resulting NADH is equivalent to the converted amount of lactose and free D-galactose. For measurement of free D-galactose alone the second set of reagents is used. Results Trueness of the lactose measurement was checked using certified reference materials with recoveries for milk, milk products, infant formula, and chocolate between 94 and 103%. Spiking experiments at low levels in almond milk, salad dressing, feta cheese, cookies, and bread revealed recoveries between 92 and 121%. Intermediate precision varied between 3.0 and 10.6% for lactose and between 6.5 and 7.8% for D-galactose. For automation, three applications with different test volumes were validated. Linearity is given from 12.5 mg/L to 12.5 g/L for lactose and 4.0 mg/L up to 6.25 g/L for galactose. Conclusions The method is robust and accurate for manual and automated applications. The method was approved as AOAC Official Method of Analysis℠. Highlights The ready-to-use components of the test kit have a shelf life of at least 24 months.