Hygiene Efficacy of Short Cycles in Domestic Dishwashers

TL;DR

This study examines how short dishwasher cycles affect hygiene, finding that detergent chemistry and temperature are key factors in killing bacteria.

Contribution

The study introduces a novel method of correlating hygiene efficacy with area under the curve (AUC) measurements from dishwasher cycle profiles.

Findings

High-tier detergents significantly reduce bacterial counts more than standard detergents in short cycles.

Dishwasher hygiene efficacy declines when main cycle temperatures drop below 50 °C.

The main cycle contributes about 10 times more to microbial reduction than the rinse cycle.

Abstract

This study investigated how factors associated with Sinner’s principle—namely temperature, time, and the chemical composition of detergents—affected the antimicrobial efficacy of domestic dishwashers, particularly during short cycles. These are of particular interest, because many consumers refrain from using long cycles while it is still unclear if short cycles can provide a sufficient level of hygiene. Thus, we chose a range of bacterial strains, including standard test strains such as Micrococcus luteus and Enterococcus faecium, as well as important foodborne pathogens such as Escherichia coli, Staphylococcus aureus, and Salmonella enterica. To account for the complexity of dishwasher cycles, we correlated hygiene efficacy with area under the curve (AUC) measurements derived from the respective cycle profiles. Our findings revealed that the reductions in M. luteus and E. faecium were minimally affected by the reference detergent. In contrast, a high-tier market detergent demonstrated a significant decrease in bacterial counts. Notably, both strains exhibited reduced efficacy at a main cycle temperature of 45 °C, suggesting that temperatures below 50 °C might represent a critical threshold at which the hygiene efficacy of domestic dishwashing processes declines. However, since food-related pathogens were more susceptible to the dishwashing process, even lower temperatures might deliver a sufficient level of hygiene. Plotting the logarithmic reduction/AUC ratio against the AUC indicated that the main cycle contributed approximately 10-fold more to microbial reduction than the rinse cycle. Furthermore, the antimicrobial impact of detergents was greatest at the lowest AUC values (i.e., during short cycles). Taken together, our results suggest that the applied chemistry may help to enhance antimicrobial performance especially in short dishwashing cycles.

Figures