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.