Analysis of nisin A, nisin Z and their degradation products by LCMS/MS

The peptides nisin A and nisin Z belong to type-A lantibiotics applied as preservatives in cheese production. The present study optimised and validated a liquid chromatography–tandem mass spectrometry (LCMS/MS) method for the analysis of nisin A in cheese. Since nisin A was not detectable in nisin-containing commercial cheese samples, an additional LCMS/MS method for the quantification of nisin Z was developed and validated. Quantification was performed by external calibration and standard addition. The latter method provided a non-significantly higher recovery rate for the tested cheese matrix. During the production of processed cheese, nisin A and nisin Z undergo significant degradation. Six degradation products of nisin A or nisin Z, respectively, were detected and assigned to nisin A/Z + H2O, nisin A/Z1–32, and nisin A/Z1–32 + H2O. In two out of eight commercial processed cheese samples, 1.6, resp. 1.7 mg nisin Z/kg cheese was measured, whereas nisin A was not detectable in any of the samples.