Detection of Listeria monocytogenes in cut melon fruit using analysis of volatile organic compounds

•VOCs were used to detect Listeria monocytogenes inoculated onto fresh cut melon cubes.•Detection was optimal after incubation of the melon cubes for 6 h at 37 °C.•Detection of inoculation levels as low as <1 log CFU/g of melon was achieved.•Thermal desorption gas chromatography time of flight mass spectrometry was used.•Whole profiles of volatile organic compounds were recorded and analysed.

Ready-to-eat fresh cut fruits and vegetables are increasingly popular, however due to their minimal processing there is a risk of contamination with human pathogens. Listeria monocytogenes is of particular concern as it can multiply even at the low temperatures used to store fresh cut products pre-sale. Current detection methods rely on culturing, which is time consuming and does not provide results in the time frame required. Growth of bacteria on a substrate alters its chemical composition affecting the profile of volatile organic compounds (VOCs) emitted. Use of VOCs as a detection method has been hampered by lack of sensitivity and robust sample collection methods. Here we use thermal desorption gas chromatography time of flight mass spectrometry (TD-GC-TOF-MS) followed by analysis with PerMANOVA to analyse VOC profiles. We can discriminate between fresh cut melon cubes inoculated with 6 log CFU/g of L. monocytogenes and uninoculated controls, as well as melon cubes inoculated with <1 log CFU/g of L. monocytogenes stored for 7 days at 4 °C and following equilibration for 6 h at 37 °C. This is a substantial advance in sensitivity compared to previous studies and additionally the collection method used allows remote sampling and transport of the VOCs, greatly facilitating analyses.