Assessing farmers market produce vendors’ handling of containers and evaluation of the survival of Salmonella and Listeria monocytogenes on plastic, pressed-card, and wood container surfaces at refrigerated and room temperature

Abstract

This study aims to assess how small produce growers handle containers and evaluate the survival of Salmonella and Listeria monocytogenes on various produce container surfaces commonly used at farmers markets, under storage conditions both at refrigerated and room temperature. In Study I, an anonymous survey was conducted to assess the practices of handling produce containers from 28 vendors at farmers markets in Morgantown, WV and 141 vendors from farmers markets in Kentucky. In Study II, plastic, pressed-card, and wood containers were trimmed (25 cm2) and inoculated with S. typhimurium and Tennessee, and two strains of L. monocytogenes, stored at 3.2 °C (22.19% RH) and 22.5 °C (50.40% RH), respectively, for 21 days and periodically analyzed for microbial populations on XLT-4 (Salmonella) and Modified-Oxford (L. monocytogenes) agars. The survey results showed that plastic, paper, and wood containers are the top three choices for small produce growers to transport and present produce at farmers markets. The pathogens decreased slower (P < 0.05) at 3.2 °C and on pressed-card and wood surfaces than at 22.5 °C and on a plastic surface. At 3.2 °C, Salmonella counts decreased (P < 0.05) from 5.27 to 5.53 to 2.63–2.84 log CFU/cm2, and L. monocytogenes decreased (P < 0.05) from 6.39 to 6.93 to 4.89–5.46 log CFU/cm2 on the three material surfaces by the end of the storage period, with the lowest (P < 0.05) survival on a plastic surface. At 22.5 °C, Salmonella populations decreased (P < 0.05) from 4.94 to 5.38 to <1.30 log CFU/cm2 (the detection limit) after 3, 9 and 12 days on plastic, pressed-card and wood surfaces, respectively. L. monocytogenes decreased (P < 0.05) from 6.39 to 6.93 to ≤1.30 log CFU/cm2 after 12, 12, and 21 days on plastic, wood and pressed-card surfaces, respectively. These results were confirmed by different mathematical survival models for analyzing pathogen inactivation rates. Vendors at farmers markets should choose plastic containers to store fresh produce and avoid storing containers at refrigerated temperature.