Determination of lactose in milk: comparison of methods

A new enzymatic method based on the spectrophotometric measurement of reduced NAD+ (beta-nicotinamide-adenine dinucleotide) at 340 nm has been evaluated by comparing it with the AOAC copper reduction method. Ten samples of milk containing various levels of lactose were analyzed in duplicate by the enzymatic method, and 5 samples were analyzed by the copper reduction method. Statistical analysis using a factorial design revealed no statistical significance between results obtained by the 2 methods; recoveries were comparable, 97% or greater for all except one sample. There was no relationship between amount of lactose added and percent recovered.