Chlorine Dioxide, Shigella and Produce Wash Water
What one laboratory study can, and cannot, tell food businesses about biofilm, non-culturable cells and PT4 hygiene.
A Food Microbiology study examined chlorine dioxide exposure in Shigella flexneri, including biofilm behaviour, cold-stress loss of culturability and a simulated reused broccoli wash-water system. The findings help explain why the food matrix and the measurement method matter, but they do not provide a commercial dosing instruction or permission to treat produce.
The study and the evidence available
Yalin Li, Yongqi Chen, Yanling Gao, Liu Liu, Yuhuan Zhang and Xiaoxia Wu authored the paper, "Chlorine dioxide injures Shigella flexneri, weakens biofilms, and produces a VBNC-like phenotype under cold stress: matrix-limited efficacy in broccoli wash water" (doi 10.1016/j.fm.2026.105258). The publisher assigns it to Food Microbiology volume 141, January 2027, article 105258.
This guide was prepared from the publisher's abstract, highlights, introduction and limited section preview. The complete methods and results were not accessible during review. The 2026 DOI string and record history are not treated here as proof of a particular online publication date.
What was tested
The researchers used one laboratory strain, S. flexneri ATCC 12022. They examined planktonic injury, biofilm formation and mature-biofilm properties, cold exposure combined with chlorine dioxide below the study's minimum inhibitory concentration, short-term metabolic responses, and performance in a simulated reused broccoli wash-water matrix.
The study did not test a ChloroKlean product. It was not a commercial processing-line trial, and the simulated broccoli system should not be treated as representative of every crop, soil load, organic load, water-reuse pattern or plant design.
Cell injury and biofilm findings
The accessible report describes increased outer-membrane permeability and leakage, stronger oxidative-stress signals, lower intracellular ATP and reduced kit-defined membrane-associated ATPase activity after chlorine dioxide exposure. These observations are consistent with linked envelope, oxidative and energy-related injury under the study conditions.
Chlorine dioxide also inhibited biofilm formation and reduced mature-biofilm biomass. The authors reported weaker biofilm metabolic activity, surface adhesion, auto-aggregation, hydrophobicity and extracellular polymeric substance components. These are laboratory findings for one strain and do not establish removal of a mixed, mature food-plant biofilm.
Why the authors say VBNC-like
Under combined cold stress at 4 degrees C and sub-inhibitory chlorine dioxide exposure, the S. flexneri cells lost culturability while retaining residual physiological activity and altered morphology. The authors therefore describe a VBNC-like phenotype rather than complete cell death.
VBNC-like is the correct limit of the accessible evidence. The preview does not establish successful resuscitation, infectivity or illness risk from those cells. A culture-negative result after a stressful exposure is not, by itself, proof that all cells are dead, but this study does not support the opposite claim that the non-culturable cells remained infectious.
The broccoli wash-water result
The publisher's highlights report that the broccoli wash-water matrix limited inactivation to approximately 1 log under the experiment's conditions. This is evidence of matrix-limited performance in that simulated reused wash water, not a general reduction claim for fresh produce or commercial wash systems.
Produce wash water can contain organic material and suspended solids that consume or shield against an oxidant. The study supports validating performance in the real process matrix rather than transferring a result from clean laboratory broth. It does not supply a practical concentration, contact time or reuse limit for an operator.
What the study does and does not establish
It establishes that aqueous chlorine dioxide injured this S. flexneri strain, weakened several measured biofilm properties, and produced loss of culturability with residual physiological signals under combined cold and sub-inhibitory exposure. It also shows that the simulated broccoli wash-water matrix substantially limited the reduction measured in the experiment.
It does not prove a confirmed VBNC state, resuscitation or infectivity. It does not demonstrate a validated commercial produce-wash process, direct food-contact permission, shelf-life extension or compliance with food law. It tested neither ChloroKlean nor a ChloroKlean use pattern, so it cannot substantiate a product-specific efficacy or dosing claim.
Where PT4 fits
PT4 covers biocidal products used for hygiene in food and feed areas, including certain equipment, containers, utensils, surfaces and pipework associated with production or processing. A food business may use a product for a particular PT4 equipment or surface application only where that intended use is permitted by the applicable product position and label.
An experimental treatment involving food or wash water does not by itself establish permission to add a biocide directly to produce wash water. Direct produce contact also raises separate food-law, process-water, residue and rinse questions. Confirm the exact intended use, GB BPR status, label directions and food-law requirements before use. This guide sets no dose.
Practical lesson for food-area hygiene
For permitted PT4 equipment and surface uses, the general lesson is to clean away soil and matrix before disinfection, apply the product exactly as labelled, and verify the outcome in the real process rather than relying on a broth result. Culture can remain useful, but unexpected negative results after a sub-inhibitory stress should be interpreted with the sampling plan and other evidence.
A higher concentration is not the automatic response to a matrix effect. Process design, water replacement, cleaning, solids control, contact conditions, monitoring and any required rinse all belong in the site's food-safety plan and must remain within the product label and applicable law.
How to assess evidence for a PT4 hygiene decision
Use this sequence to review evidence and permissions. It is not a produce-wash or disinfectant dosing protocol.
Define the intended use
State whether the proposal concerns equipment, a food-contact surface, CIP pipework, process water or direct contact with produce.
Check the permission
Confirm the product's applicable GB BPR position, label use, contact conditions and rinse instructions, plus separate food-law requirements.
Match the evidence to the process
Compare organism, matrix, temperature, organic load, surface and endpoint with the real operation. Do not transfer a laboratory exposure as a plant dose.
Validate and verify
Use a documented site validation and ongoing monitoring plan that recognises the limits of culture-only results.
Expert Insights
About the Reviewer
Gavin Owen
Managing Director, ChloroKlean
Gavin Owen leads ChloroKlean's technical and commercial operations, bringing over 20 years of experience in industrial chemical distribution and water treatment. He oversees product development, regulatory compliance strategy, and the company's BPR compliance programme across PT2, PT4, PT5, and PT11 product types. Gavin works directly with water treatment professionals, facilities managers, and public health engineers across healthcare, leisure, food processing, and industrial sectors.
Frequently Asked Questions
Common questions about this topic, answered by our technical team.
Scope and safe-use note
- This is an evidence interpretation, not a dosing instruction, product label or process validation.
- Use a biocidal product only for an intended use permitted by its applicable regulatory position and label.
- Assess direct food contact, process water, residues and rinsing under the applicable food law as well as GB BPR.
The cited study tested one Shigella flexneri strain in laboratory systems and simulated reused broccoli wash water. It did not test ChloroKlean or establish permission for direct produce washing.
Related Resources
Continue exploring our knowledge base and product information.
Mixed-species dairy biofilms in food processing
Why single-strain laboratory findings can understate the tolerance of plant biofilms.
VBNC bacteria after disinfection
Why culture negativity alone is not proof of elimination.
Biofilm monitoring and verification
Match each monitoring method to the question it can answer.
Food-safe disinfectant guide
How product labels, PT4 scope and food-area hygiene fit together.
PT4 food and feed area hygiene
The product-type context for authorised equipment and surface hygiene uses.
Sources & References
This article references guidance from the following authoritative sources:
- Chlorine dioxide injures Shigella flexneri, weakens biofilms, and produces a VBNC-like phenotype under cold stress: matrix-limited efficacy in broccoli wash water
Industry Standard - Food Microbiology, volume 141, January 2027, article 105258
- In situ generation: active substances vs biocidal products
HSE - Health and Safety Executive, GB BPR
- UK authorised biocidal products
HSE - Health and Safety Executive, GB BPR
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