Validation of Enzytec™ Liquid D-/L-Lactic Acid for Enzymatic Determination of D- and L-Lactic Acid in Selected Foods and Beverages: Official Method 2024.08 First Action.

Abstract

Produced naturally by lactic acid bacteria, L-lactic acid is found in many fermented milk products such as yogurt, and also in pickled vegetables, cured meats, and fish. It also serves as a quality parameter in wine, beer, whole egg, whole egg powder, and juices. To validate the performance of the Enzytec™ Liquid D-/L-Lactic acid for the determination of the sum of D- and L-lactic acid in food and beverages such as milk and (fermented) milk products, fermented vegetable products, wines, beer, fruit and vegetable juices, and eggs and egg powder. The kit contains two ready-to-use components, which makes handling easy and suitable for automation. Both lactic acids react in the presence of NAD and D- or L-Lactate dehydrogenase to pyruvate and NADH. The NADH formed is equivalent to the amount of D-/L-lactic acid converted. Ascorbic acid, 3-hydroxybutyric acid, and sulfite were found to have a low activity at concentrations higher than 0.5, 0.05, and 0.1 g/L, respectively. Oxaloacetic acid and D-fructose do not interfere at concentrations at or below 0.2 and 20 g/L, respectively. The calculated LOD when using a test solution volume of 100 µL is 3 mg/L, and the LOQ is 10 mg/L. The practical upper measurement range is 600 mg/L. Relative intermediate precision was between 3.8 and 5.3% for pineapple juice, sauerkraut juice, wine, and liquid egg. Cream cheese Certified Reference Materials showed a recovery between 98 and 103%. A reference wine was found with a recovery of 104%. For automation, three applications with different test solution volumes were validated. Linearity is given from 4 up to 3125 mg/L. The method is robust and accurate and was approved as an AOAC Official Method of Analysis℠. The ready-to-use components of the test kit have a shelf life of at least 24 months.