Use of dishwashers fails to inactivate foodborne pathogens in home-canned model foods

Abstract

Risky home canning techniques are still performed for food preservation due to limited science-based recommendations. This study aimed to evaluate the inactivation of Shiga toxin-producing Escherichia coli O157:H7, Salmonella enterica (ser. Typhimurium, Enteritidis, and Infantis) and Listeria monocytogenes during home canning with a household dishwasher. The 450 mL of blended tomato (acidic liquid food) and potato puree (non-acidic solid food) were prepared with 1.5 % salt and 25 mL vinegar as model foods in glass jars (660 mL). The two model foods were sterilized, then inoculated with separate cocktails of each pathogen at 106–107 CFU/g. The prepared jars were placed in the bottom rack of a dishwasher and subjected to the following cycles: economic (50 °C, 122 min), express (60 °C, 54 min), and intensive (70 °C, 96 min). Temperature changes in jars were monitored by using thermocouples during heat treatment. Within the center of the jars, temperatures were measured as 45 to 53 °C in blended tomato and 44 to 52 °C in potato puree during all tested dishwasher cycles, respectively. The economic cycle treatment reduced S. enterica, E. coli O157:H7, and L. monocytogenes populations by 3.1, 4.6, and 4.2 log CFU/g in blended tomato (P ≤ 0.05), where a <1.0 log reduction was observed in potato puree (P > 0.05). All pathogens showed similar heat resistance during the express cycle treatment with a log reduction ranging from 4.2 to 5.0 log CFU/g in blended tomato and 0.6 to 0.7 log CFU/g in potato puree. Reduction in L. monocytogenes population was limited (0.6 log CFU/g) compared to E. coli O157:H7 (2.0 log CFU/g) and S. enterica (2.7 log CFU/g) in blended tomato during the intensive cycle treatment (P ≤ 0.05). Dishwasher cycles at manufacturer defined settings failed to adequately inactivate foodborne pathogens in model foods. This study indicates that home-canned vegetables may cause foodborne illnesses when dishwashers in home kitchens are used for heat processing.