Reduction Foodborne Pathogens and Surrogate Microorganism on Citrus Fruits after Lab- and Pilot-scale Finishing Wax Application

Abstract

After finishing waxes are applied, citrus fruits are typically dried at 32–60°C for 2–3 min before final packing. The survival of Listeria monocytogenes, Salmonella, and Enterococcus faecium NRRL B-2354 was evaluated under laboratory conditions on lemons after applying one of four finishing waxes (F4, F6, F8, and F15) followed by an ambient hold or heated (50 or 60°C) drying step. The reduction of inoculated microorganisms during drying was significantly influenced by wax type and temperature, with greater reductions at higher temperatures. Greater reductions after waxing and drying at 60°C were observed with L. monocytogenes (2.84–4.44 log) than with Salmonella (1.65–3.67 log), and with Salmonella than with E. faecium (0.99–2.93 log). The survival of Salmonella inoculated at 5.8–5.9 log/fruit on lemons and oranges after applying wax F6 and drying at 60°C was evaluated during storage at 4 and 22°C. The reductions of Salmonella after waxing and drying were 1.7 log; additional reductions during storage at 4 or 22°C were 1.40–1.43 or 0.18–0.29 log, respectively, on waxed lemons, and 0.56–1.02 or 0.54–0.57 log, respectively, on waxed oranges. Under pilot-scale packinghouse conditions with wax F4, mean and minimum reductions of E. faecium ranged from 2.15 to 2.89 and 1.64 to 2.12 log, respectively. However, E. faecium was recovered by whole-fruit enrichment (limit of detection: 0.60 log CFU/lemon) but not by plating (LOD: 1.3 log CFU/lemon) from uninoculated lemons run with or after the inoculated lemons. The findings should provide useful information to establish and implement packinghouse food safety plans.

Keywords

• Citrus wax
• Enterococcus faecium NRRL B-2354
• Listeria monocytogenes
• Salmonella
• Storage