Growth of Escherichia coli O157:H7 and Listeria monocytogenes in Packaged Fresh-Cut Romaine Mix at Fluctuating Temperatures during Commercial Transport, Retail Storage, and Display

Abstract

Temperature abuse during commercial transport and retail sale of leafy greens negatively impacts both microbial safety and product quality. Consequently, the effect of fluctuating temperatures on Escherichia coli O157:H7 and Listeria monocytogenes growth in commercially-bagged salad greens was assessed during transport, retail storage, and display. Over a 16-month period, a series of time-temperature profiles for bagged salads were obtained from five transportation routes covering four geographic regions (432 profiles), as well as during retail storage (4,867 profiles) and display (3,799 profiles). Five different time-temperature profiles collected during 2 to 3 days of transport, 1 and 3 days of retail storage, and 3 days of retail display were then duplicated in a programmable incubator to assess E. coli O157:H7 and L. monocytogenes growth in commercial bags of romaine lettuce mix. Microbial growth predictions using the Koseki-Isobe and McKellar-Delaquis models were validated by comparing the root mean square error (RMSE), bias, and the acceptable prediction zone between the laboratory growth data and model predictions. Monte Carlo simulations were performed to calculate the probability distribution of microbial growth from 8,122,127,472 scenarios during transport, cold room storage, and retail display. Using inoculated bags of retail salad, E. coli O157:H7 and L. monocytogenes populations increased a maximum of 3.1 and 3.0 log CFU/g at retail storage. Both models yielded acceptable RMSEs and biases within the acceptable prediction zone for E. coli O157:H7. Based on the simulation, both pathogens generally increased <2 log CFU/g during transport, storage, and display. However, retail storage duration can significantly impact pathogen growth. This large-scale U.S. study-the first using commercial time/temperature profiles to assess the microbial risk of leafy greens-should be useful in filling some of the data gaps in current risk assessments for leafy greens.

Improving spinach quality and reducing energy costs by retrofitting retail open refrigerated cases with doors

“…Overall, for all spatial locations, temperatures in the open case were 24% non-compliant with FDA Food Code. These findings are consistent with a study by Zeng et al (2014) who reported that 30% of temperatures recorded for fresh-cut romaine mix stored for 3 days in refrigerated retail display, were above 5 C.…”

“…However, maintaining these temperature conditions during transportation and storage at the retail terminus has been a challenge due to the heterogeneous logistics across the chain. Zeng et al (2014) observed that non-uniform temperatures during commercial transport, retail storage and display promote the growth of Escherichia coli O157:H7 and Listeria monocytogenes in packaged fresh-cut romaine mix, with populations increasing to a maximum of $3 logs CFU/g at retail storage, consistent with temperature abuse between 8 C and 16 C. Across the cold chain, no pathogen growth occurred when temperatures remained at 4 C or below (Zeng et al, 2014).…”

Survival of Salmonella and Escherichia coli O157:H7 on Strawberries, Basil, and Other Leafy Greens during Storage

“…Foodborne outbreaks occurred with strawberries and basil after transport and storage, suggesting survival of E. coli 0157:H7 or Salmonella on both commodities, even in adverse environ ments. Although survival of these pathogens has been studied on leafy greens, such as spinach (45,54), escarole (1,54), and especially, on fresh-cut iceberg or romaine lettuce (11,20,22,58,61), and growth models are available for iceberg lettuce (37,47) to predict growth of E. coli under temperature abuse, limited information is available about the survival of E. coli 0157:H7 and Salmonella on basil leaves during storage (29,35). Moreover, no information about the survival of Salmonella or E. coli 0157:H7 on basil leaves during storage at 15°C is available, which is the recom mended temperature to maintain quality during storage.…”

Microbial ecology of fresh vegetables

“…Mean measured tem peratures for transport and display in retail cases were rarely above 6 °C. While E. coli O157:H7 growth was essentially static during this time, L. monocytogenes barely proliferated under transport conditions (≤0.6 log cfu/g) but increased up to 1.1 log cfu/g during three days of housing in display cases (Zeng et al, 2014). This study illustrated the importance of main taining an uninterrupted cold chain.…”