Food safety practices worldwide have been impacted by the COVID-19 pandemic caused by SARS-CoV-2. There is mounting evidence that SARS-CoV-2 can persist on fresh produce like cabbage for extended periods, acting as a vehicle for viral transmission (Casanova et al., 2010; Chin et al., 2020; Riddell et al., 2020; Sahun et al., 2023; van Doremalen et al., 2020). Our study aimed to quantify SARS-CoV-2 RNA removal rates from fresh cabbage during refrigerated storage and after treatment with neutral electrolyzed water (NEW) or calcium hypochlorite (Ca(ClO)2).
We demonstrated that SARS-CoV-2 RNA persisted on cabbage for up to 1 week of refrigerated storage, despite a > 1 log reduction in viral load. This corroborates other findings showing SARS-CoV-2 survival for days to weeks on various fresh produce items at refrigeration temperatures (Casanova et al., 2010; Chin et al., 2020). The viral RNA detection after 7 days, albeit at lower levels, indicates there is potential for SARS-CoV-2 transmission via contaminated vegetables even after refrigerator storage. However, RNA persistence does not necessarily mean viable or infectious virus is still present (Kampf et al., 2020; Onakpoya et al., 2022). Follow-up infectivity assays are warranted to ascertain if refrigerated cabbage still poses an infection risk after 1 week.
Various factors can influence SARS-CoV-2 survival on fresh produce, including produce type, surface structure, physiological state, and storage conditions like temperature, humidity and lighting (Benkeblia, 2021; Chin et al., 2020; Riddell et al., 2020). The waxy, hydrophobic surface of cabbage has the potential to protect SARS-CoV-2 from environmental stressors. Lower storage temperatures between 1–4°C also favor extended SARS-CoV-2 persistence across produce items (Jung et al., 2023; Liu et al., 2021). Considering these factors, cabbage provides favorable conditions for prolonged SARS-CoV-2 survival during refrigerated storage.
In another study on the effect of freezer temperatures on the stability of the SARS-CoV-2 virus on agricultural products including berries, it was demonstrated that the virus can remain viable when stored at freezer temperatures for up to one month on berries that have been contaminated with this virus (Esseili et al., 2022). In another study conducted to detect the genetic material of the SARS-CoV-2 virus on several agricultural products including green leafy vegetables, using RT-PCR testing and estimating the viral genome load based on CT values, it was shown that this virus can potentially be transmitted to humans through these products (Rafieepoor et al., 2022). Based on assessments and studies conducted and observation of the presence of the coronavirus on packaged food products such as lettuce and Risk of transmission, the Chinese government has made RT-PCR testing mandatory on these imported products (Butot et al., 2022) Xie found that the SARS-Cov-2 surrogate virus MHV-JHM could survive on packaging materials surfaces for 28 days at − 40°C and − 20°C. It could also survive for up to 14 days on foam and plastic surfaces at 4°C (Xie et al., 2023). The ability of Phi 6 and animal coronaviruses to survive for varying extents on some meat and fish products when stored refrigerated or frozen was a significant and concerning finding in Bailey’s study (Bailey et al., 2022).The more resilient foodborne viruses like norovirus and hepatitis A virus are concerning surrogates for SARS-CoV-2 (Baker & Gibson, 2022; Chin et al., 2020). Since these viruses remain infectious for weeks to months under refrigeration, SARS-CoV-2 could potentially exhibit similar hardiness. Direct comparisons of SARS-CoV-2 survival and infectivity versus other viral pathogens on cabbage and lettuce would provide valuable insights into the relative contamination risks.
For inactivation methods, we found NEW significantly more effective than Ca(ClO)2 for removing SARS-CoV-2 RNA from contaminated cabbage when applied at the same concentration of 200 mg/L total chlorine. NEW achieved a > 3 log reduction while Ca(ClO)2 only achieved a 0.5 log reduction. The superior efficacy of NEW is likely due to its mixture of chlorine species (Cl2, ClO-, ClO2) which have higher oxidation potential than the Ca(ClO)2-derived hypochlorous acid (HOCl) (Rebezov et al., 2022; Vorobjeva et al., 2004; Yan et al., 2021). Other studies corroborate NEW's effectiveness against SARS-CoV-2 on fresh produce, with > 3 log reductions on strawberries and lettuce at similar chlorine concentrations (Fritz et al., 2022; Komaikul et al., 2022; Wu et al., 2022).
While NEW and Ca(ClO)2 solutions have shown efficacy for SARS-CoV-2 viral titer reduction and inactivation on produce, treatment effects can vary based on produce type and surface characteristics (Loveday et al., 2021; Riddell et al., 2020). Cabbage presents a unique challenge as a leafy green with hydrophobic waxy cuticle. Comparing NEW and Ca(ClO)2 against SARS-CoV-2 on other fresh produce items could provide broader insights into disinfection efficacy and matrix effects. Treatment protocol factors like concentration, contact time, temperature and pH also warrant investigation, as they impact chlorine chemistry and oxidation capacity (Rebezov et al., 2022). Process optimization is needed to maximize viral inactivation while minimizing quality defects that can arise from over-exposure to chlorine-based sanitizers (Mendoza et al., 2022).
Since NEW disrupted SARS-CoV-2 RNA more effectively than Ca(ClO)2 in our study, it could be a promising disinfectant to reduce coronavirus contamination and transmission risks from fresh cabbage and leafy greens. NEW solutions are generated on-site via electrolysis of diluted NaCl solution, providing a practical sanitization approach amenable to fresh-cut operations (Rebezov et al., 2022). However, more research is needed on the impacts to nutritional and organoleptic properties at effective anti-SARS-CoV-2 concentrations.
Non-chlorine alternatives should also be considered. Ozonated water sprayed on lettuce reduced murine norovirus by > 3 log within 1 minute of exposure (Habibi Najafi & Haddad Khodaparast, 2009; Xue et al., 2023). High hydrostatic pressure processing inactivated feline calicivirus on cabbage after 5 minutes at 250 MPa (Kingsley et al., 2007). And cold plasma rapidly degraded SARS-CoV-2 on strawberries, reaching > 3 log reduction in viral RNA within 5 minutes (Chen et al., 2020; Thomas et al., 2023). These emerging non-thermal technologies could provide chlorine-free options to enhance safety while maintaining quality.
A limitation of this study is that only viral RNA degradation was evaluated. Further analyses should examine NEW and Ca(ClO)2 effects on actual viral particle and infectivity reduction through cell culture assays. Since RNA persistence does not necessarily indicate presence of infectious virus, such infectivity data would provide additional insights into true disinfection efficacy (Ahmed et al., 2020; Lin et al., 2022; Zonta et al., 2016). Testing on live SARS-CoV-2 virus is also needed.
Ideally, future produce safety studies should incorporate epidemiological evidence linking produce to SARS-CoV-2 infections. As an RNA virus, SARS-CoV-2 is susceptible to degradation during digestive processes (Ahmed et al., 2020; Azuma et al., 2020). Even if low residual virus persists post-disinfection, oral ingestion may not pose a significant infection risk (Alvis-Chirinos et al., 2022). Quantitative microbial risk assessments combining foodborne virus survival, disinfection efficacy, exposure levels, and dose-response will help contextualize what contamination levels actually presents a transmission hazard(Anelich et al., 2020).
Overall, this study indicates refrigeration alone may not eliminate risks of SARS-CoV-2 cross-contamination from fresh cabbage and leafy greens. Disinfection treatments like NEW could provide an additional barrier. Uncertainties remain about viral infectivity on produce and effective mitigation measures. As global food systems respond to COVID-19, research-based evidence and technologies to mitigate virus transmission via fresh produce can support public health protection. Further investigation of practical postharvest inactivation measures is warranted to maintain produce safety while retaining nutrition and quality.