Simultaneous determination of Nisin A and Nisin Z in nutritional food by liquid chromatography tandem mass spectrometry (LC-MS/MS)

A method for the simultaneous determination of Nisin A and Nisin Z in nutritional products by LC-MS/MS has been developed. Sample treatment was performed by ultrasonic extraction using a mixture of 0.1 M CH3COONH4 buffer solution - 1.0 M NaCl (pH 2.0): MeOH (1:1, v/v) at room temperature for 10 minutes. Extracts were then cleaned through C18 solid phase extraction column (500 mg, 3 mL) and analyzed on LC-MS/MS instrument using a C18 column (100 mm × 2 mm × 1.7 µm) with ESI (+) mode. The method was validated for linear calibration curve in the range of 10 - 1,000 µg/L; relative standard deviation (RSD) 2.12 - 5.77%; recovery 80.1 - 105%, meeting AOAC requirements. The method has been applied to analyze 25 samples of nutritious food collected from the local markets (including: liquid milk, powdered milk, butter, cheese, nutritious powder), showing that two samples were detected both Nisin A and Nisin Z.