Stability study of a nisin/natamycin blend by LC-MS.

Nisin and natamycin are natural preservatives used in a broad range of food products. In the present study, the stability of an aqueous nisin/natamycin blend (pH 4.0) for the beverage market was tested at room temperature (22 °C) under dark conditions by means of liquid chromatography. Both an HPLC-UV and a UPLC-MS method were developed to monitor the concentration of natamycin and nisin, respectively. After 6 months at room temperature (22 °C) under dark conditions, the nisin/natamycin blend (pH 4.0) still contained 85% of the original amount of nisin and 95% of natamycin. Even after 1 year, 50% of nisin and 90% of natamycin remained in the formulation. The resulting degradation products were studied by means of high resolution mass spectrometry. For both nisin and natamycin, degradation products originating from hydration (natamycin + H2O; nisin + H2O) and oxidation reactions (natamycin + O; nisin + O; nisin + 2O) were observed.