Isotopic dilution assay development of nisin A in cream cheese, mascarpone, processed cheese and ripened cheese by LC-MS/MS method

摘要

The current food safety concern for food integrity demands the availability of an accurate, easy and reliable analytical tool for assay development of nisin A in cheese. To address this, we report the application of isotopically labelled peptide sequence MSTKDFNLDLVSVSKKDSGASP(R) (without thioether bridges) as internal standard for determination of nisin A in cream cheese, mascarpone, processed cheese and ripened cheese without the need for matrix-matched calibration by triple-quadrupole mass spectrometry. Full method validation was performed according to the modified Commission Decision 2002/657/EC criteria and method robustness was checked on 10 random cheese samples. Internal standard provided significant improvement (p 0.05) in method precision for determination of nisin A in all four types of cheese. Significant losses (p 0.05) for Nisin A in cheese was observed one week later. A fit-for-purpose method using internal standard procedure for accurate quantitation of Nisin A in cheese becomes available.