Application of capilary electroforesis with contactless conductivity detector for determination of nisin in fermented milk product

Abstract

The demand for natural antibacterial agents is growing all over the world. Nisin is the only antibacterial peptide which is allowed for conservation of some products and is recognized as food additive (E234). Nisin may be added into food not only as pure agent, but also may be produced in food media by bacteriocins (nisin) producing lactic acid bacteria. Therefore, the analysis of nisin in food matrix is an important task. The aim of this study was to apply capillary zone electrophoresis coupled with 2nd generation capacitance-to-digital technique based contactless conductivity detector for the separation and determination of nisin in fermented milk products. Sample preparation included following steps: (i) extraction/dilution and (ii) centrifugation. Capillary electrophoresis of samples was performed in 0.5 M (pH 2.53) acetic acid background electrolyte, using 13 kV voltage and hydrodynamic injection at 50 mbar*40s. Determination of natural preservatives in fermented milk products is a complex task due to following reasons: (i) concentrations below detection limit, (ii) complex matrix and interfering compounds, (iii) low recovery, and (iv) complex sample preparation needed. Capillary electrophoresis with contactless conductivity method was optimized for the separation of nisin in fermented milk and fresh cheese samples. The precision, accuracy and sensitivity of the method were determined. Optimized conditions allowed precise, accurate, sensitive (limit of detection: 0.19 ng/ml) and most importantly - requiring very simple sample preparation, determination of nisin. Simple, precise, accurate and robust capillary zone electrophoresis - contactless conductivity detection analysis procedure developed allowing determination of nisin in fermented milk products.