Enzymatic Determination of Lactate in Liquid Milk and Milk Powder

We have evaluated a new enzymatic method for determining the quantity of lactate contained in liquid milk or milk powder. In the conventional method, hydrazine is required to ensure quantitative enzymatic reaction. However, the new method using glutamic-pyruvic transaminase (GPT) can be conveniently performed at room temperature. The optical density at 340nm is measured using 0.5mol/L glycyl-glycine buffer solution (pH 10.5) at room temperature (25°C) 40 minutes after the start of the reaction. The recovery in liquid milk or milk powder ranged from 87 to 113%.The results obtained in two different laboratories coincided at the 5% level of significance at lactate levels above 20mg/100g s. n. f., but deviated quite widely below that level. We conclude that this method should be of practical value.