A recent laboratory study has provided new insights into the efficacy of peroxyacetic acid (PAA) and chlorine dioxide in mitigating microbial contamination and cross-contamination during the washing of potatoes during processing. The findings support the development of targeted, evidence-based sanitation protocols for the potato processing industry, particularly in settings where water reuse is practiced.

Potatoes, the third most consumed food crop globally, are prone to surface contamination by foodborne pathogens such as Escherichia coli, Listeria monocytogenes, and noroviruses due to their contact with soil and irrigation water. Despite their prevalence in foodborne illness outbreaks, root vegetables have received limited attention in disinfection research. For example, the study cited U.S. Centers for Disease Control and Prevention (CDC) data, which shows that, from 2016–2023, approximately 1,109 cases of foodborne illness caused by Escherichia coli, Bacillus, norovirus, and Salmonella were reported in relation to the consumption of potatoes, potato salads, and potato-based sandwiches. Additionally, in frozen potato processing, contamination by L. monocytogenes has recently been reported as a long-term challenge.

In this context, the researchers aimed to evaluate the microbial reduction efficacy of PAA and chlorine dioxide, assess cross-contamination risks during batch washing, and examine the impact of wash water reuse under simulated industrial conditions.

The researchers purchased potatoes with visible soil, confirmed those potatoes to be free of the test pathogens (L. monocytogenes, E. coli, and murine norovirus), and then inoculated the potatoes with those pathogens. The potatoes were then washed using tap water without a disinfectant, wash water with PAA, and wash water with chlorine dioxide. The researchers also conducted a cross-contamination scenario during washing with disinfectants by washing non-inoculated and inoculated potatoes in the same batches, and evaluated the efficacy of disinfectants in a wash water reuse scenario.

Overall, the researchers observed significant reductions in microbial populations and inhibition of cross-contamination when PAA and chlorine dioxide were used during the potato washing process, except for chlorine dioxide against norovirus. PAA proved effective at lower concentrations and shorter contact times than chlorine dioxide. Specifically, the researchers found:

• E. coli: PAA at 40 parts-per-million (ppm) achieved a reduction of 1.86–2.51 log colony forming unit (CFU)/potato; treatment at 120 ppm for 3 minutes led to a 0.68 log higher reduction than treatment with 40 ppm PAA. Chlorine dioxide at 80 ppm achieved a reduction of 1.98–2.97 log CFU/potato. While PAA was effective even when applied at 40 ppm and for 1 minute, chlorine dioxide led to a notable reduction only when applied at concentrations over 80 ppm.
• L. monocytogenes: PAA at 120 ppm for 1 minute reduced bacterial counts by 2.59 log CFU/potato. Chlorine dioxide at 80 ppm for 5 minutes achieved a comparable reduction of 2.55 log CFU/potato.
• Norovirus: PAA at greater than or equal to 40 ppm for 5 minutes reduced viral loads by up to 2.28 log PFU/potato. Chlorine dioxide, however, showed no statistically significant reduction in murine norovirus.

Regarding cross-contamination during batch washing, the researchers found that, in the simultaneous washing scenario, untreated tap water washing led to cross-contamination with E. coli and L. monocytogenes at 3.01 and 3.22 log CFU/potato, respectively. PAA completely inhibited E. coli transfer, while chlorine dioxide allowed limited transfer (0.83–1.30 log CFU/potato). Both disinfectants failed to fully prevent L. monocytogenes transfer. Cross-contamination by norovirus was not detected even in untreated tap water.

In the water reuse scenario, the reuse of wash water significantly increased cross-contamination with E. coli and L. monocytogenes. Although PAA effectively prevented E. coli transfer, L. monocytogenes persisted across multiple washes. Cross-contamination with norovirus was also not detected in any reused water samples, suggesting lower cross-contamination risk.

The study underscores the importance of selecting appropriate disinfectants based on the target microorganism. PAA demonstrated superior efficacy at lower concentrations and shorter contact times, making it a promising candidate for industrial applications where water reuse and bulk washing are common. However, the persistence of L. monocytogenes even after treatment highlights the need for enhanced control strategies, especially under high organic loads.

Several limitations were noted. Organic matter levels were not quantified, which may influence disinfectant performance, and key water quality parameters such as pH and oxidation-reduction potential were not monitored. Additionally, culture-based detection methods may underestimate pathogen persistence due to microorganisms in viable but non-culturable (VBNC) states. Future research should incorporate advanced detection techniques and real-time monitoring of water quality metrics to better simulate industrial conditions and optimize disinfection protocols.

Published in the Journal of Food Science, the study was authored by researchers from Chung-Ang University, Seoul, Republic of Korea.