Validation of Enzytec™ Liquid L-Lactic Acid for Enzymatic Determination of L-Lactic Acid in Selected Foods and Beverages: Official Method 2024.07 First Action.

BACKGROUND: Produced naturally by lactic acid bacteria, L-lactic acid is found in many fermented milk products and also in pickled vegetables, cured meats, and fish. It serves as a quality parameter in wine, beer, whole egg, whole egg powder, and juices. OBJECTIVE: To validate the performance of the Enzytec™ Liquid L-Lactic acid for the determination of L-lactic acid in food and beverages such as milk and (fermented) milk products, fermented vegetable products, wines, beer, fruit and vegetable juices, egg, and egg powder. METHODS: The method is based on enzymes that are part of a prepackaged kit that contains two ready-to-use components which are suitable for automation. L-lactic acids react in the presence of NAD and L-lactate dehydrogenase to pyruvate and NADH. The NADH formed is equivalent to the amount of L-lactic acid converted. RESULTS: Ascorbic acid, 3-hydroxybutyric acid, and sulfite were found to interfere at concentrations higher than 0.2, 0.05, and 0.05 g/L in the test solution, respectively. Oxaloacetic acid and D-fructose do not interfere at concentrations at or below 0.2 and 10 g/L, respectively. The calculated LOD when using a test volume of 100 µL is 3.8 mg/L and the limit of quantitation is 10 mg/L. The practical upper measurement range is 600 mg/L. Relative intermediate precision was between 3.0 and 7.3% for pineapple juice, sauerkraut juice, wine, and liquid egg. Certified reference materials (cream cheese and wine) showed recoveries between 100 and 104%. For automation, three applications with different test volumes were validated. Linearity is given from 0.75 to 3125 mg/L. CONCLUSIONS: The method is robust and accurate for manual and automated applications. The method was approved as an AOAC Official Method of Analysis℠. HIGHLIGHTS: The components of the test kit have a shelf life of at least 24 months.