Rapid identification, by use of the LTQ Orbitrap hybrid FT mass spectrometer, of antifungal compounds produced by lactic acid bacteria
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Fungal contamination of food causes health and economic concerns. Several species of lactic acid bacteria (LAB) have antifungal activity which may inhibit food spoilage fungi. LAB have GRAS (generally recognised as safe) status, allowing them to be safely integrated into food systems as natural food preservatives. A method is described herein that enables rapid screening of LAB cultures for 25 known antifungal compounds associated with LAB. This is the first chromatographic method developed which enables the rapid identification of a wide range of antifungal compounds by a single method with a short analysis time (23 min). Chromatographic separation was achieved on a Phenomenex Gemini C18 100A column (150 mm × 2.0 mm; 5 μm) by use of a mobile-phase gradient prepared from (A) water containing acetic acid (0.1%) and (B) acetonitrile containing acetic acid (0.1%), at a flow rate of 0.3 µL min−1. The gradient involved a progressive ramp from 10–95% acetonitrile over 13 min. The LC was coupled to a hybrid LTQ Orbitrap XL fourier-transform mass spectrometer (FTMS) operated in negative ionisation mode. High mass accuracy data (<3 ppm) obtained by use of high resolution (30,000 K) enabled unequivocal identification of the target compounds. This method allows comprehensive profiling and comparison of different LAB strains and is also capable of the identification of additional compounds produced by these bacteria.
KeywordsLAB Antifungal compounds LTQ Orbitrap XL High mass accuracy data LC–FTMS
We gratefully acknowledge funding from the Food Institutional Research Measure (FIRM) Department of Agriculture, Fisheries and Food Ireland (project reference 08RDC607). The Council of Directors, Technological Sector Research-Strand III 2006 Grant Scheme, awarded to Dr A. Furey is also acknowledged for funding the formation of the “Team Elucidate” research group. The Higher Education Authority (Programme for Research in Third-Level Institutions, Cycle 4 (PRTLI IV) National Collaboration Programme on Environment and Climate Changes: Impacts and Responses is also acknowledged. We also thank Dr Mary Lehane and Dr Sharon Hutchinson for their critical reading of the manuscript.
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