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.

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.