Improved Pretreatment Method for Determination of Nisins A and Z and Monitoring in Cheese Using Liquid Chromatrography-Tandem Mass Spectrometry

The peptide nisin produced by Lactococcus lactis subsp. lactis is known to be one of the natural preservatives that are used in various foods including cheese products. This study optimized and validated a liquid chromatography-tandem mass spectrometry method for determining nisin A and nisin Z in cheese. Processed and natural cheeses were used for method validation. In addition, this study investigated the content of nisin A and nisin Z in 140 cheese samples comprised of imported and domestic cheese. The nisin A and nisin Z contents of 140 cheese samples were determined. An extraction solution consisting of 0.1 M acetate buffer containing 1 M NaCl (pH 2.0) and methanol (NaCl/MeOH, 1:1 v/v) was the optimal solution for nisin extraction from cheese. The limits of quantification of nisin A and nisin Z were approximately 10.2 and 12.6 μg/kg, respectively. For processed cheese and natural cheese, the recoveries were 80.1–107.3 % for nisin A and 74.4–113.9 % for nisin Z and low coefficients of variation. In monitoring study, nisins A and Z were detected in only three soft processed cheese out of 140 samples. The proposed analysis procedure can be used as an efficient tool for determination of nisin A and nisin Z in cheese using liquid chromatography-tandem mass spectrometry (LC-MS/MS).