Is your lunch salad safe to eat? Occurrence of bacterial pathogens and potential for pathogen growth in pre-packed ready-to-eat mixed-ingredient salads

Abstract

As part of a trend toward healthy convenience foods, ready-to-eat (RTE) mixed-ingredient salads have become popular products among consumers. A mixed-ingredient salad contains combinations of raw (e.g. leafy vegetables and tomatoes) and processed (e.g. chicken, salmon, ham, pasta and couscous) ingredients. Contamination of leafy vegetables can occur during any step in the production chain and, since there is no step that kills pathogens, a completely safe final product can never be guaranteed. Meat ingredients, for example poultry meat and ham, are generally heat-treated before preparation, but may be contaminated after this treatment, e.g. when diced or sliced. When several ingredients are mixed together, cross-contamination may occur. Preparation of mixed-ingredient salads requires human handling, which presents an additional risk of bacterial contamination. With high-protein ingredients, e.g. cooked meat, the mixed-ingredient salad represents an excellent substrate for bacterial growth. This article reviews current knowledge regarding human bacterial pathogen prevalence in mixed-ingredient salads and the potential for pathogen growth in this product during storage.

Estimating Listeria monocytogenes Growth in Ready‐to‐Eat Chicken Salad Using a Challenge Test for Quantitative Microbial Risk Assessment

“…L. monocytogenes growth rates would probably be different when considering the individual components of the salad, as every ingredient of the studied RTE chicken salad including green leaves, cooked chicken breast, hard cheese, and bacon has the potential ability to support L. monocytogenes growth (Horita et al., 2018; Patterson, Mackle, & Linton, 2011; Valero, Hernández, Esteban‐Carbonero, & Rodríguez‐Lázaro, 2018; Ziegler, Kent, Stephan, & Guldimann, 2019). Still, mixed‐ingredients salads, especially those including leafy vegetables and cooked chicken, seem to be a better substrate for bacterial growth than its individual components, due to neutral pH, high water activity, and high concentration of accessible nutrients, allowing the growth of L. monocytogenes during storage under temperature abuse (Söderqvist, 2017).…”

“…bacterial growth than its individual components, due to neutral pH, high water activity, and high concentration of accessible nutrients, allowing the growth of L. monocytogenes during storage under temperature abuse (Söderqvist, 2017). With the μ max obtained at 4°C, the maximum concentration of L. monocytogenes that may be present at the production stage in order to comply with the mandatory limit of 100 cfu/g at the end of shelf-life was determined, considering that the consumer respects the recommended commercial shelflife (144 hours-6 days) and storage temperature.…”

Changes in Consumers’ Food Purchase and Transport Behaviors over a Decade (2010 to 2019) Following Health and Convenience Food Trends

“…Increases in total food purchase and transport time suggest the importance of time-temperature control. Although food safety guidelines suggest following the "2-h rule and 1-h rule" (i.e., limit exposure of food to the danger zone to 1-2 h to prevent pathogen growth and/or toxin production under the temperature that can cause the growth or survival of foodborne bacteria in foods) [14,15,17,52], these results highlight the probability of long-term exposure of food products to ambient environments during purchasing and following transportation steps. Because the actual time that food is exposed to danger zones is determined by time-temperature control factors such as the purchasing order (i.e., buying perishable foods last) and the transportation environment (i.e., placing refrigerated foods in cooler bags with icepacks as a countermeasure for temperature abuse of perishable foods) [14,17,19], the importance of consumers' proper behaviors should be stressed.…”

Listeria, Then and Now: A Call to Reevaluate Patient Teaching Based on Analysis of US Federal Databases, 1998‐2016

“…Patient teaching should emphasize that heating foods to 165°Ft (74°C) kills L monocytogenes , whereas cooling or freezing a previously contaminated dish does not eliminate the pathogen. For these reasons, buying ready‐to‐eat food that can be heated at home is safer than buying ready‐to‐eat food that remains refrigerated all the way to consumption, especially if the refrigerated food contains multiple ingredients, any one of which could have been contaminated. All frozen vegetables and entrees need to be heated thoroughly.…”