Lactose Concentration in Low-Lactose and Lactose-Free Milk, Milk Products, and Products Containing Dairy Ingredients by High Sensitivity Enzymatic Method (K-LOLAC), Collaborative Study: Final Action 2020.08.

BACKGROUND: The AOAC Stakeholder Panel on Strategic Food Analytical Methods issued a call for methods in 2018 for the measurement of lactose in low-lactose and lactose-free products under Standard Method Performance Requirements (SMPR®) 2018.009. Megazyme's Lactose Assay Kit (K-LOLAC) was reviewed and accepted as a First Action Official Method in 2020 (2020.08).

OBJECTIVE: A collaborative study was conducted to evaluate the to evaluate the reproducibility of AOAC Method 2020.08 for the measurement of lactose concentration in low-lactose and lactose-free milk, milk products, and products containing dairy ingredients.

METHOD: Samples are deproteinated and clarified by treatment with Carrez reagents, then free glucose is removed using a glucose oxidase and catalase treatment system. Quantification of lactose is based on the hydrolytic activity of β-galactosidase, which hydrolyses lactose to glucose and galactose. Any remaining free D-glucose is first measured using a Hexokinase (HK)/Glucose 6-phosphate dehydrogenase (G-6PDH)/6-phosphogluconate dehydrogenase (6-PGDH) based assay procedure, and then β-galactosidase is added to hydrolyse the lactose in the same reaction vessel with concurrent measurement of the released D-glucose. The samples analysed included a number of lactose free and low-lactose milk samples, lactose-free infant formula, lactose-free milkshake, lactose-free adult nutritional drink, lactose-free cream and lactose-free cheese.

RESULTS: All materials had repeatability relative standard deviations (RSDr) <7%. The reproducibility relative standard deviation (RSDR) varied from 3.8 to 14.9% with seven of the 10 test samples having an RSDR of < 10%.

CONCLUSIONS: The Lactose Assay Kit (K-LOLAC) meets the requirements for reproducibility set out under SMPR 2018.009.

HIGHLIGHTS: The Lactose Assay (K-LOLAC) is a robust, simple and reproducible method for analysis of lactose in foodstuffs and beverages.