Survival of Listeria monocytogenes and Salmonella in finishing waxes used for fresh citrus fruits

Citrus fruits are typically waxed before packaging to prevent water loss and extend shelf-life. The survival of Listeria monocytogenes and Salmonella was evaluated in 15 different commercial finishing waxes used for fresh citrus in California. Survival of L. monocytogenes and Salmonella in citrus finishing waxes depended on wax type. Over 24 h at 4 and 22 °C, populations of L. monocytogenes declined more slowly than or equal to Salmonella in all finishing waxes except wax F8 (organic, beeswax based, non-morpholine). Over 24 h of storage at 4 °C, L. monocytogenes populations declined by > 4 log (below the detection limit by enrichment, 0.3 log CFU/mL) in waxes F4, F7, F8, and F9. Population declines of 1.2–2.8 log were observed in waxes F5, F10, F11, F13, and F14 and of <1.0 log in waxes F1, F2, F3, F6, F12, and F15. With the exception of waxes F2 (polyethylene based, non-morpholine) and F6 (shellac based, non-morpholine), greater declines of L. monocytogenes were observed over 24 h in most waxes when the storage temperature was increased to 22 °C. During long-term storage at 4 °C, L. monocytogenes declined by > 5 log after 5, 10, 30, 30, and 135 days in waxes F3, F1, F15, F12, and F6, respectively. L. monocytogenes populations in all waxes stored at 22 °C fell below the detection limit by enrichment within 20 days except for wax F2. In two separate lots of wax F2, L. monocytogenes populations inoculated at ∼4 or ∼6 log CFU/mL declined by1.6–2.6 log by day 10 and then increased to 5.4 to 5.7 log CFU/mL on day 20. Citrus packinghouse hazard assessments and food safety plans should consider the survival of foodborne pathogens in commercial citrus finishing waxes.