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.