Thermal Inactivation of Listeria monocytogenes and Salmonella during Water and Steam Blanching of Vegetables

Abstract

Thermal inactivation of Listeria monocytogenes and Salmonella was evaluated on peas, spinach, broccoli, potatoes, and carrots that were treated with hot water and steam. One gram-positive bacterium, L. monocytogenes, and one gram-negative bacterium, Salmonella, were selected as pertinent human pathogens for evaluation. Samples were inoculated with a composite of five strains each of L. monocytogenes and Salmonella to achieve approximately 10 to 10 CFU/g. Inoculated samples were treated with hot water at 85 and 87.8°C and with steam at 85 and 96.7°C for up to 3.5 min. A greater than 5-log reduction of L. monocytogenes and Salmonella was achieved on all products within 0.5 min by hot water blanching at 85 and 87.8°C. Steam blanching at 85°C reduced Salmonella populations by greater than 5 log on spinach and peas within 2 min and on carrots and broccoli within 3.5 min. Populations of Salmonella were reduced by more than 5 log within 1 min on carrot, spinach, and broccoli and within 2 min on peas by steam blanching at 96.7°C. Steam blanching at 85°C reduced L. monocytogenes populations by more than 5 log on carrots and spinach within 2 min and on broccoli and peas within 3.5 min. L. monocytogenes populations were reduced more than 5 log within 1 min on carrot, spinach, peas and broccoli by steam blanching at 96.7°C. Longer treatment times and higher temperatures were required for steam-blanched samples than for samples blanched with hot water. Results suggest that hot water and steam blanching practices commonly used by the frozen vegetable industry will achieve the desired 5-log lethality of L. monocytogenes and Salmonella and will enhance microbiological safety prior to freezing.

The public health risk posed by Listeria monocytogenes in frozen fruit and vegetables including herbs, blanched during processing

“…L. monocytogenes was reduced more than 5 log 10 within 1 min on carrot, spinach, peas and broccoli by steam blanching at 96.7°C. The study by Ceylan et al (2017) revealed that shorter t/T treatment is applicable when using hot water blanching. However, either hot water or steam blanching can achieve the desired 5 log 10 reduction in L. monocytogenes when adequate t/T combinations are applied.…”

Urgent scientific and technical assistance to provide recommendations for sampling and testing in the processing plants of frozen vegetables aiming at detecting Listeria monocytogenes

“…Common blanching temperatures range from 70 to 100ºC for a few minutes, whereas steam blanching requires applying steam for longer time period (Ceylan et al, 2017). Common blanching temperatures range from 70 to 100ºC for a few minutes, whereas steam blanching requires applying steam for longer time period (Ceylan et al, 2017).…”

“…However, longer treatment times and higher temperatures were required for steamblanching compared to hot water blanching (Ceylan et al, 2017). peas, spinach, broccoli, potatoes and carrots) were inoculated with approximately 10 8 -10 9 CFU/g L. monocytogenes and Salmonella, respectively and treated with hot water at 85 and 87.8ºC and steam at 58 and 96.7ºC for up to 3.5 min.…”

“…monocytogenes is widespread in the environment and can be found in soil, water, sewage and decaying vegetation (EFSA BIOHAZ Panel, 2018). Several studies have highlighted that L. monocytogenes persists in manufacturing equipment and in damp areas of the production environment that may develop into niche harbourage sites (Carpentier and Cerf, 2011;Ceylan et al, 2017). Several studies have highlighted that L. monocytogenes persists in manufacturing equipment and in damp areas of the production environment that may develop into niche harbourage sites (Carpentier and Cerf, 2011;Ceylan et al, 2017).…”

“…Types of technologies used for blanching and the purpose of blanching (adapted from Xiao et al, 2017) Blanching can have an impact on the microorganisms present in the FVH by reducing foodborne pathogens associated with FVH such as L. monocytogenes (Bozkurt et al, 2015;Ceylan et al, 2017).…”