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.

Background: 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.

Objective: 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, egg and egg powder.

Methods: 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.

Results: 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.

Conclusions: The method is robust and accurate and was approved as AOAC Official Method of Analysis℠.

Highlights: The ready-to-use components of the test kit have a shelf life of at least 24 months.