DIN 10054:2015-05

This document describes an enzymatic/reflectometric screening method (test strip detection) to determine the L- and D-lactic acid (L- and D-lactate) content in milk and dairy products. The L- and D-lactic acid content and the L- and D-lactate content determined by this method are calculated as L- and D-lactic acid. Lactic acid (L- and D-form) is oxidized by nicotinamide adenine dinucleotide in the presence of the enzymes L-lactate dehydrogenase and D-lactate dehydrogenase to pyruvic acid (pyruvate). The reduced form of nicotinamide adenine dinucleotide formed in these reactions reduces a tetrazolium salt to a formazan in the presence of diaphorase. The amount of formazan formed is proportional to the amount of L-lactic acid or D-lactic acid present. The amount of formazan formed is determined by reflectometry. The balance of reactions, which is largely on the side of lactic acid, is shifted to the side of pyruvic acid (pyruvate) and NADH by the reaction of the reduced form of nicotinamide adenine dinucleotide with the tetrazolium salt. The enzymes L-lactate dehydrogenase and D-lactate dehydrogenase are stereospecific so that the two isomeric lactic acids can be determined side by side. The responsible committee is NA 057-05-13 AA "Milch und Milchprodukte - Probenahme- und Untersuchungsverfahren" ("Milk and milk products - Methods of sampling and analysis") at DIN.