Dynamics of Listeriamonocytogenes and Salmonella enterica on Cooked Vegetables During Storage.

Fresh vegetables have been linked to multiple foodborne outbreaks in the U.S., with Listeria monocytogenes and Salmonella enterica identified as leading causes. Beyond raw vegetables, cooked vegetables can also pose food safety concerns due to improper cooking temperature and time combinations or postcooking contamination. Cooked vegetables, having had their native microbiota reduced through heat inactivation, might provide an environment that favors the growth of pathogens due to diminished microbial competition. While the risks associated with raw vegetables are recognized, the survival and growth of pathogens on cooked vegetables remain inadequately studied. This study investigated the growth kinetics of both L. monocytogenes and S. enterica on various cooked vegetables (carrot, corn, onions, green bell pepper, and potato). Vegetables were cooked at 177°C until the internal temperature reached 90°C and then cooled to 5°C. Cooled vegetables were inoculated with a four-strain cocktail of either L. monocytogenes or S. enterica at 3 log CFU/g, then stored at different temperatures (5, 10, or 25°C) for up to 7 days. Both pathogens survived on all vegetables when stored at 5°C. At 10°C, both pathogens proliferated on all vegetables, with the exception of L. monocytogenes on pepper. At 25°C, the highest growth rates were observed by both pathogens on carrot (5.55 ± 0.22 and 6.42 ± 0.23 log CFU/g/d for L. monocytogenes and S. enterica, respectively). S. enterica displayed higher growth rates at 25°C compared to L. monocytogenes on all vegetables. Overall, these results bridge the knowledge gap concerning the growth kinetics of both S. enterica and L. monocytogenes on various cooked vegetables, offering insights to further enhance food safety.

Growth Kinetics of Listeria monocytogenes and Salmonella enterica on Dehydrated Vegetables during Rehydration and Subsequent Storage.

Dehydrated vegetables have low water activities and do not support the proliferation of pathogenic bacteria. Once rehydrated, vegetables can be incorporated into other foods or held for later use. The aim of this study was to examine the survival and proliferation of Listeria monocytogenes and Salmonella enterica on dehydrated vegetables during rehydration and subsequent storage. Carrots, corn, onion, bell peppers, and potatoes were heat dehydrated, inoculated at 4 log CFU/g, and rehydrated at either 5 or 25 °C for 24 h. Following rehydration, vegetables were stored at 5, 10, or 25 °C for 7 d. Both L. monocytogenes and S. enterica survived on all vegetables under all conditions examined. After 24 h of rehydration at 5 °C, pathogen populations on the vegetables were generally <1.70 log CFU/g, whereas rehydration at 25 °C resulted in populations of 2.28 to 6.25 log CFU/g. The highest growth rates during storage were observed by L. monocytogenes on potatoes and S. enterica on carrots (2.37 ± 0.61 and 1.63 ± 0.18 log CFU/g/d, respectively) at 25 °C when rehydration occurred at 5 °C. Results indicate that pathogen proliferation on the vegetables is both rehydration temperature and matrix dependent and highlight the importance of holding rehydrated vegetables at refrigeration temperatures to hinder pathogen proliferation. Results from this study inform time and temperature controls for the safety of these food products.

Growth Kinetics of Listeria monocytogenes on Cut Red Cabbage.

ABSTRACT: Listeria monocytogenes is a foodborne pathogen associated with fresh produce vectors such as leafy greens. Recent outbreaks and recalls associated with red cabbage-containing salads have brought attention to this food commodity. Although data on the proliferation of L. monocytogenes are available for different varieties of whole and cut white cabbage, no information is available on the fate of this pathogen on red cabbage. The aim of this study was therefore to explore the survival of L. monocytogenes on cut red cabbage (Brassica oleracea L. var. capitata f. rubra) during storage at different temperatures. Red cabbage was cut into pieces (5 by 4 cm) and spot inoculated with a six-strain cocktail of rifampin-resistant L. monocytogenes, resulting in an initial inoculation level of 4 log CFU/g. Samples were stored at 5 or 10°C for 14 days or at 25°C for 7 days. At intervals during storage, L. monocytogenes was enumerated by homogenization of cabbage with Butterfield's phosphate buffer, and serial dilutions were plated onto brain heart infusion agar supplemented with rifampin. No growth of L. monocytogenes was observed on cut red cabbage during storage at 5°C, and only minimal proliferation was observed at the higher temperatures. Significant population increases of 0.58 and 1.07 log CFU/g were determined after 3 days of storage at 10 and 25°C, respectively; however, a significant decrease of 0.77 log CFU/g from 3 to 14 days was also observed at 10°C. The modeled growth rates for L. monocytogenes on cut red cabbage stored at 5 and 10°C were 0.11 ± 0.03 and 0.27 ± 0.07 log CFU/g/day, with calculated times to a 1-log CFU/g increase of 9.51 and 3.70 days, respectively; however, L. monocytogenes did not achieve a 1-log increase at either temperature in this study. At 25°C, the modeled growth rate of L. monocytogenes on cut red cabbage was 1.15 ± 0.36 log CFU/g, leading to a calculated and an observed 1-log increase in 0.87 and 3.00 days, respectively. Results from this study aid in understanding the fate of L. monocytogenes on cut red cabbage during storage at different temperatures.

Restaurant Date-Marking Practices Concerning Ready-to-Eat Food Requiring Time and Temperature Control for Safety.

Certain foods are more vulnerable to foodborne pathogen growth and formation of toxins than others. Lack of time and temperature control for these foods can result in the growth of pathogens, such as Listeria monocytogenes, and lead to foodborne outbreaks. The Food and Drug Administration's (FDA) Food Code classifies these foods as time/temperature control for safety (TCS) foods and details safe cooking, holding, and storing temperatures for these foods. The FDA Food Code also includes a date-marking provision for ready-to-eat TCS foods that are held for >24 h. The provision states that these foods should not be held in refrigeration for >7 days and should be marked with the date or day by which the food should be "consumed on the premises, sold, or discarded." To learn more about restaurants' date-marking practices, the Centers for Disease Control and Prevention's Environmental Health Specialists Network (EHS-Net) conducted observations and manager interviews in 359 restaurants in 8 EHS-Net jurisdictions. Managers reported that they date marked ready-to-eat TCS foods more often than data collectors observed this practice (91% vs. 77%). Observation data showed almost a quarter of study restaurants did not date-mark ready-to-eat TCS foods. In addition, restaurants with an internal date-marking policy date marked 1.25 times more often than restaurants without such a policy and chain restaurants date marked 5.02 times more often than independently owned restaurants. These findings suggest that regulators and the retail food industry may improve food safety and lower the burden of foodborne illness in the United States if they target interventions to independent restaurants and encourage strong date-marking policies.

Assessing Employee Health Policies for Reporting and Excluding Ill Food Employees in Restaurants within the United States.

ABSTRACT: Preventing ill food employees from spreading pathogens to food and food contact surfaces remains an important objective of retail food safety policy in the United States. Since 2005, the U.S. Food and Drug Administration (FDA) has recommended food establishments implement employee health policies that include requirements for the exclusion or restriction of ill food employees and reporting, to the person in charge, symptoms or diagnosis of certain diseases transmitted by food. However, the incorporation of this recommendation has not been widely studied. The purpose of this exploratory study was to assess the presence and prevalence of employee health policies at fast-food and full-service restaurants in the United States. More than 50% of fast-food and full-service restaurants were found to have nonexistent employee health policies for each of the five recommended components specified in the FDA Food Code. Results showed 17.41% of fast-food restaurants and 12.88% of full-service restaurants had all five recommended components. Moreover, most restaurants with all five recommended employee health policy components were part of a multiple-unit operation and were found to have more developed food safety management systems than restaurants with none of the recommended components. Further attention and research into the impediments associated with developing and implementing employee health policies in restaurants is warranted.

Allergen Removal and Transfer with Wiping and Cleaning Methods Used in Retail and Food Service Establishments.

ABSTRACT: Preventing the transfer of allergens from one food to another via food contact surfaces in retail food environments is an important aspect of retail food safety. Existing recommendations for wiping and cleaning food contact surfaces is mainly focused on preventing microorganisms, such as bacteria and viruses, from contaminating foods. The effectiveness of these wiping and cleaning recommendations for preventing the transfer of food allergens in retail and food service establishments remains unclear. This project investigated (i) allergen removal from surfaces by wiping with paper wipes, terry cloth, and alcohol quaternary ammonium chloride (quat) sanitizing wipes; (ii) cleaning of allergen-contaminated surfaces by using a wash-rinse-sanitize-air dry procedure; and (iii) allergen transfer from contaminated wipes to multiple surfaces. Food contact surfaces (stainless steel, textured plastic, and maple wood) were contaminated with peanut-, milk- and egg-containing foods and subjected to various wiping and cleaning procedures. For transfer experiments, dry paper wipes or wet cloths contaminated with allergenic foods were wiped on four surfaces of the same composition. Allergen-specific lateral flow devices were used to detect the presence of allergen residues on wiped or cleaned surfaces. Although dry wipes and cloths were not effective for removing allergenic foods, terry cloth presoaked in water or sanitizer solution, use of multiple quat wipes, and the wash-rinse-sanitize-air dry procedure were effective in allergen removal from surfaces. Allergens present on dry wipes were transferred to wiped surfaces. In contrast, minimal or no allergen transfer to surfaces was found when allergen-contaminated terry cloth was submerged in sanitizer solution prior to wiping surfaces. The full cleaning method (wash-rinse-sanitize-air dry) and soaking the terry cloth in sanitizer solution prior to wiping were effective at allergen removal and minimizing allergen transfer.

Temperature and pH affect copper release kinetics from copper metal foil and commercial copperware to food simulants.

Copper (Cu) metal and alloys are used in cookware and other food contact surfaces due to their desirable properties for various applications. However, Cu metal can ionise and subsequently transfer to food and beverages under certain conditions. Here, we tested how pH and temperature affected Cu release kinetics using model systems utilising Cu metal foil and commercially available copperware. Cu foil and copperware were exposed to food simulants composed of 3% (w:w) aqueous solutions of citric acid, malic acid, acetic acid, or deionised (DI) water at temperatures ranging from 4°C to 60°C. An additional pilot experiment tested how simulated long-term cleaning affected subsequent Cu release from lined and unlined copperware to 3% citric acid. Food simulants were then analysed by ICP-MS for total Cu. After 180 min, incubation of Cu metal foil with acid-containing food simulants at 4°C resulted in Cu release ranging from 8.7 - 14.0 µg cm-2, while 21.5-38.1 µg cm-2 was released at 60°C. In contrast, Cu transfer from metal foil to DI water was relatively low, with <0.6 µg cm-2 released after 180 min at 60°C. With citric acid food simulant, lined copperware released between 0.6 and 3.0 µg Cu cm-2 over 180 min at the set temperatures, while unlined copperware released approximately 25-45 fold higher amounts of Cu (26.9-74.6 µg cm-2) over this same time period. In contrast, use of DI water food simulant resulted in Cu release of <0.1 µg cm-2 for the lined copperware and <2 µg cm-2 for the unlined type. No significant effect of simulated long-term cleaning on Cu release from copperware was observed. These data indicate that Cu release is affected by temperature and pH, and that specific steps can be taken to limit Cu metal release from food contact surfaces to foods and beverages.

Food Safety Management Systems, Certified Food Protection Managers, and Compliance with Food Safety Practices Associated with the Control of Listeria monocytogenes in Foods at Restaurants.

HIGHLIGHTS: Proper cold holding and date marking practices help control Lm growth in foods. Most restaurants had ≥1 instance of improper cold holding. Less than 50% of all cold holding observations were found to be out of compliance. Restaurants in areas requiring date marking of food were more likely to date mark. CFPM did not predict out-of-compliance observations when FSMS effects were considered.

Advancing Retail Food Policy Debates: Estimating the Risk of Contaminated Servings of Food Attributed to Employee Food Handling Practices in Retail Food Establishments.

Food employee contamination of ready-to-eat foods through improper food handling practices is an important contributing factor for foodborne illness in retail and food service establishments. Decreasing the incidence of improper food handling practices is a frequent topic of retail food policy deliberations that often involves estimating the degree to which a proposed policy might affect a specific food handling practice. However, the potential reduction in contaminated servings of food, and therefore foodborne illnesses avoided, associated with a given proposed policy change, is all too often uncertain. This article discusses the components, assumptions, and applications of the food handling practices model, a quantitative model that estimates the impact of food handling practices on servings of food moving along three consecutive stages: the contamination stage, the pathogen control stage, and the foodborne illness stage. To our knowledge, this article is the first time the model has been presented in an academic platform, and we also explore unique and interesting aspects of the model not addressed in publicly available documents. Risk-based estimates for contaminated servings of food attributed to changes in one or multiple food handling practices are derived that provide an important link between increased compliance with proper food handling practices and public health. Model estimates show that decreases in the incidence of inappropriate food handling practices lead to varying levels of contaminated food servings avoided, depending on the food handling practice. The ability to derive such estimates provides stakeholders and the general public with a means of understanding the relative impact of proposals to reduce improper food handling and to help inform regulatory food safety policy discussions and decision making.

Growth Kinetics of Listeria monocytogenes in Cut Produce.

Cut produce continues to constitute a significant portion of the fresh fruit and vegetables sold directly to consumers. As such, the safety of these items during storage, handling, and display remains a concern. Cut tomatoes, cut leafy greens, and cut melons, which have been studied in relation to their ability to support pathogen growth, have been specifically identified as needing temperature control for safety. Data are needed on the growth behavior of foodborne pathogens in other types of cut produce items that are commonly offered for retail purchase and are potentially held without temperature control. This study assessed the survival and growth of Listeria monocytogenes in cut produce items that are commonly offered for retail purchase, specifically broccoli, green and red bell peppers, yellow onions, canned green and black olives, fresh green olives, cantaloupe flesh and rind, avocado pulp, cucumbers, and button mushrooms. The survival of L. monocytogenes strains representing serotypes 1/2a, 1/2b, and 4b was determined on the cut produce items for each strain individually at 5, 10, and 25°C for up to 720 h. The modified Baranyi model was used to determine the growth kinetics (the maximum growth rates and maximum population increases) in the L. monocytogenes populations. The products that supported the most rapid growth of L. monocytogenes, considering the fastest growth and resulting population levels, were cantaloupe flesh and avocado pulp. When stored at 25°C, the maximum growth rates for these products were 0.093 to 0.138 log CFU/g/h and 0.130 to 0.193 log CFU/g/h, respectively, depending on the strain. Green olives and broccoli did not support growth at any temperature. These results can be used to inform discussions surrounding whether specific time and temperature storage conditions should be recommended for additional cut produce items.

Quantitative Risk Assessment of Norovirus Transmission in Food Establishments: Evaluating the Impact of Intervention Strategies and Food Employee Behavior on the Risk Associated with Norovirus in Foods.

We developed a quantitative risk assessment model using a discrete event framework to quantify and study the risk associated with norovirus transmission to consumers through food contaminated by infected food employees in a retail food setting. This study focused on the impact of ill food workers experiencing symptoms of diarrhea and vomiting and potential control measures for the transmission of norovirus to foods. The model examined the behavior of food employees regarding exclusion from work while ill and after symptom resolution and preventive measures limiting food contamination during preparation. The mean numbers of infected customers estimated for 21 scenarios were compared to the estimate for a baseline scenario representing current practices. Results show that prevention strategies examined could not prevent norovirus transmission to food when a symptomatic employee was present in the food establishment. Compliance with exclusion from work of symptomatic food employees is thus critical, with an estimated range of 75-226% of the baseline mean for full to no compliance, respectively. Results also suggest that efficient handwashing, handwashing frequency associated with gloving compliance, and elimination of contact between hands, faucets, and door handles in restrooms reduced the mean number of infected customers to 58%, 62%, and 75% of the baseline, respectively. This study provides quantitative data to evaluate the relative efficacy of policy and practices at retail to reduce norovirus illnesses and provides new insights into the interactions and interplay of prevention strategies and compliance in reducing transmission of foodborne norovirus.