Salmonella, E. coli O157:H7 and Listeria monocytogenes (Lm) are three of the most common food-related bacteria that processors have to control. While all three are relatively easy to control through the cooking process, once a product, such as meat, is cooked and used as an ingredient, environmental Lm (on equipment harborage sites, walls and drains) can be a concern in RTE processing and packaging because it survives and does well at temperatures from -0.4°C to 45°C (31°F to 113°F), with 37°C (98.6°F) being an optimum temperature. Not only that, but Lm is also able to survive at a relatively low water activity (aW < 0.90) and a broad pH range between 4.6 and 9.5, as well as tolerate salt conditions up to 20%. And Lm loves to build up a biofilm to protect itself in cracks and crevices in machines and floor drains, making it difficult to inactivate and remove. Boar’s Head recently closed a facility due to Lm infestation.

Lm’s survivability and motility make cleaning and sanitation practices a challenge for any food facility. USDA’s FSIS found meat and fat residue from the previous day’s production on processing and packaging equipment at Boar’s Head, providing an excellent environment for biofilms to form. Other discoveries included condensation from cooling equipment on RTE product and several structural issues that could hold moisture and contribute to wet conditions — the environment that Lm loves.

This article looks at effective methods of cleaning and sanitation (C&S) that can be employed to kill bacteria and prevent pathogen buildup, especially Lm. Several methods can be applied, depending on specific applications.

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Can “Green” Do the Job?

“Green” chemicals, such as plant-derived essential oils and biodegradable surfactants, are increasingly adopted in the food industry due to their environmental benefits, says Karim-Franck Khinouche, Novolyze founder and CEO. While these alternatives can be effective against certain pathogens, their efficacy against resilient bacteria, like Lm, may vary. In scenarios where Lm is present or biofilms have formed, traditional chemicals, like peracetic acid or sodium hydroxide (NaOH), are often more reliable. For challenging sanitation tasks, selecting appropriate traditional chemicals is crucial.

“Whatever chemical is ultimately found to be effective for a particular application, quickly and proactively addressing future contamination requires trusted and comprehensive documentation of not only the effective chemical, but also the sanitation process used in its control,” Khinouche adds.

Novolyze’s Sanitation Complete software solution enhances the effectiveness of both green and traditional chemicals by digitalizing Master Sanitation Programs, including environmental monitoring and task management. This comprehensive approach ensures that sanitation practices are optimized, aligning with food safety objectives and promoting sustainability.

On the subject of biodegradability, all Diversey cleaning products meet biodegradability requirements, according to the EU Detergents Regulation (EC) No 648/2004, says Fabrizio Tardioli, associate director, global marketing food and beverage at Diversey, a Solenis Company.

“Sustainability is top-of-mind for many customers and consumers, so we are making notable efforts to develop and commercialize solutions beyond these regulations, adopting solutions and raw materials that have an even better sustainability profile versus the previous ones — for example, utilizing products that are coming from renewable sources or are 100% biodegradable,” Tardioli adds.

The market demands non-toxic chemicals (or chemicals that present less of a hazard for operators) and more environmentally friendly chemicals and products, Tardioli says. “In the food and beverage industry, sometimes we need to deal with extremely heavy soils and contamination where the possibility to utilize very mild chemistries is limited. If we specifically talk about Listeria spp and monocytogenes, we need to clarify a few points. The first one is that as a [bacterium], listeria is not difficult to kill, so we do not need any particularly harsh chemistry or super-aggressive product to kill it. However, listeria is extremely difficult to eradicate from food processing factories, and it requires many different practices and solutions to mitigate it and control it — from cleaning and sanitation to GMP, hygienic design, [and] water and humidity control.”

Relying and focusing on only one C&S approach will most likely lead to failure to control Lm on the production floor, Tardioli says. The focus should not solely be on the nature of the detergent or the sanitizer/disinfectant, but rather the whole site’s procedures and risk mitigation practices. In the recent Boar’s Head outbreak, the root cause was “…meat and fat residue from the previous day’s production on the equipment, including packaging equipment.” Other instances included dripping condensation “on exposed product” and “cracks, holes and broken flooring that could hold moisture and contribute to wet conditions.”

“From this limited information, it is already clear that there was more than one aspect of the site’s procedures that was not fully under control: inadequate cleaning, monitoring and verification, water and condensation management, facility management and hygienic design, to mention a few areas,” Tardioli says.

Therefore, if a biocide product meets the local regulation, whether “green” or not, this will be absolutely fine to control listeria, but only if all of the surrounding aspects (cleaning, monitoring, facility, GMP, hygienic design, etc.) are also properly managed, Tardioli adds.

Electrolyzed Water: Practical for Food and Beverage?

Electrolyzed water, i.e., generating hypochlorous acid, is recognized for its antimicrobial properties and utilized in various sanitation applications, says Novolyze’s Khinouche. “Its effectiveness can be comparable to traditional chemicals, like peracetic acid or NaOH, depending on factors such as concentration and application method. Electrolyzed water is particularly suited for surface disinfection and environments where chemical residues are a concern. However, its cost-effectiveness varies based on implementation scale and operational considerations.”

“This method is not more effective than traditional chemicals, neither in cleaning nor in disinfection,” cites Diversey’s Tardioli. “It has the advantage of local production versus storage of formulated chemicals; however, it also requires the investment costs for the generator and electricity consumption. In some circumstances, the solutions generated can also come with a serious risk of corrosion due to elevated chloride levels.”

“The best application for electrolyzed water occurs in a pool, spa or premise plumbing scenario,” says Rich Walsh, Ecolab senior staff scientist. While some have tried within food and beverage contexts, its undesirable side effects typically outweigh its utility as a cleaning solution. Electrolyzed water requires high levels of sodium chloride, or salt, to function. Because the chlorine (and in turn, hypochlorous acid) generated from this process is not a complete conversion, the end result is a copious amount of salt in the system at all times. This salt solution splashes and sprays onto nearby surfaces, and after the water has evaporated away, the remaining salt becomes highly corrosive to many common materials — even stainless steel. In addition to shortening the usable lifespan of core equipment, this corrosion creates the ideal conditions for pitting, which creates harborage points for microbiota and increases the risk of a serious microbiological event.

“Finding the most effective and sustainable cleaning and/or sanitation option heavily depends on context,” says Joy Herdt, Ecolab senior staff scientist. “Within the food and beverage space, this context varies significantly based on what’s being manufactured or processed. For example, producers of certain food types, such as cereals, nutrition bars, grains or nuts, will want to contain and control water when cleaning and sanitizing to minimize the risk of water becoming a vector for microbiota, which may include pathogens. This is what we’re talking about when we talk about dry cleaning — a methodology wherein the tightly controlled application of cleaners and sanitizers limits the amount of water (and water-related risk) in the cleaning and sanitization processes.”

About Dry Cleaning: Superheated Steam, Chlorine Dioxide and UV-C Light

Dry steam cleaning utilizes steam with minimal moisture content, making it suitable for sanitizing equipment in both high-moisture environments, such as meat production, and low-moisture facilities, such as bakeries, says Novolyze’s Khinouche. Its advantages include effective microbial reduction and the ability to reach intricate areas without excessive water use. However, its efficacy in physically removing biofilms and heavy residues may be limited, necessitating mechanical action or chemical interventions. Operators should use appropriate personal protective equipment (PPE) to prevent burns or injuries.

“Steam cleaning can be used in specific applications, generally where there is a relatively low level of soil to be removed and where the use of water is not welcomed, as it may affect the production or the product food safety,” says Diversey’s Tardioli.

“We need to consider that to clean is to dissolve a soil and displace it from the surface to the drain (or anywhere the specific case requires),” Tardioli adds. “Wet cleaning makes use of chemicals to saponify, oxidize and physically break the bonds of contamination so it can be resolubilized in water and washed down the drain. Steam can effectively act on some soils, but we still need to displace it somewhere, and this is not always practical, safe for the operators or financially attractive to be performed in greater scale across all applications. So, this can indeed be used in specific applications where water needs to be heavily controlled and limited, but at the moment, it cannot replace traditional wet cleaning solutions in many key industries, such as meat, poultry or fish, where the majority of soils require water-based chemistries.”

Steam cleaning is not 100% “dry” because it involves steam, says Ecolab’s Walsh. But this is true of many solutions that typically fall under the dry-cleaning umbrella — they aren’t completely free of moisture, but they are specially designed to reduce the need for water in the C&S processes as much as possible. One of the major innovations in the dry-cleaning space is the development of fast-drying sanitizers.

One solution worth mentioning for its effective use against pathogenic contaminants is chlorine dioxide — a powerful antimicrobial registered with the EPA as a sterilant, says Ecolab’s Herdt. Chlorine dioxide is useful for hard-to-clean equipment, dry-cleaning environments and spaces where liquid microbials can’t quite reach. Because of its molecular size and status as a true gas, chlorine dioxide can penetrate areas where microorganisms are hiding and can’t physically be reached. And because it is a gas, it leaves no residue behind, eliminating the need for a post-clean rinse and further supporting moisture reduction.

These properties make chlorine dioxide a highly thorough and flexible option for a number of different applications. Manufacturers can target specific pieces of equipment by tarping them and creating a sealed environment, or they can isolate a product pathway within the equipment itself. They can also scale the treatment to treat a space of much larger size. Of course, chlorine dioxide treatments must be applied under very controlled conditions to prevent workers from being exposed to the gas. Typically, this involves a partial or full shutdown of the facility, with production downtime ranging anywhere from a few to several hours, depending on the amount of space being treated, Herdt says.

UV-C light is effective for surface sterilization of equipment, particularly in low-moisture environments where traditional wet-cleaning methods are impractical, says Novolyze’s Khinouche. Its practicality depends on factors such as line-of-sight exposure and material compatibility. Typically, UV-C is applied after processing has concluded to avoid potential hazards to personnel and product degradation. It can be used on empty conveyor belts; however, ensuring uniform exposure is crucial. In some cases, dry steam cleaning may be preferable for its ability to remove residues physically, depending on the specific sanitation requirements.

Environmental air is another application for UV-C light. According to Diversey’s Tardioli, UV-C air disinfection systems are designed to work continuously and can be running during production and in the presence of operators without safety risks.

Ozone and Plasma Technologies

Ozone and plasma cleaning are promising chemical-free sanitation technologies that offer effective microbial reduction in various food processing applications, Khinouche says. Ozone is a powerful oxidizing agent that effectively destroys bacteria, viruses and biofilms.

Ozone is currently being utilized in large-scale food processing facilities in both gaseous and aqueous forms for surface and environmental sanitation, says Matt Lowe, president and CEO of Advanced Ozone Integration. Centrally installed aqueous ozone systems (systems that provide ozone dissolved in water) are designed to apply ozone to multiple applications, including in-process direct treatment of food products (raw and RTE), in addition to indirect application on food processing equipment. The same system then provides ozone during the cleaning/sanitation shift via spray gun hose stations for any open plant cleaning (OPC) activities.

In addition, some facilities are starting to explore aqueous ozone use for CIP and COP as a replacement for traditional sanitizers in the final sanitizing step of the CIP or COP process. Many processors successfully utilize aqueous ozone to specifically target listeria harborage areas, like floor drains. Ozone gas is also being utilized for facility environmental treatment and has been proven to treat a variety of microorganisms — including the listeria species — in hard-to-reach areas, such as refrigeration units and their drip trays. From a green standpoint, ozone is a standout. It is an oxygen-based molecule that only requires air and electricity to generate on-site, leaving only oxygen behind as a byproduct, Lowe adds. 

“We have seen ozone tested for CIP applications but not penetrate the market versus existing CIP chemistries,” says Diversey’s Tardioli. However, plasma as atmospheric pressure plasma torches can be used in cleaning, as well as sanitation of open, hard surfaces. Plasma systems may work well with robotic arms and automated systems but require a high capital investment and are typically limited to thin soil layers only. Because of that, they might work well in sanitizing an already clean and dry surface; however, they will not cut through a millimeter of soil layer. Also, air extraction might be required for operators nearby.

Plasma-based sanitation generates reactive oxygen and nitrogen species that can effectively inactivate pathogens on surfaces and in the air, says Novolyze’s Khinouche. “This technology is especially useful in environments where traditional wet sanitation is impractical, such as dry processing facilities for low-moisture foods (e.g., bakeries, snack manufacturing and powdered ingredient production). Plasma cleaning can also be applied for packaging sterilization, ensuring extended shelf life without the need for chemical preservatives.”

Choose the Right Technologies for Your Application to Control Listeria

Listeria monocytogenes (with two new outbreaks in March and unknown sources) can be pesky to control, as we’ve already discussed. System integrators and chemical suppliers stand ready to help with the technology solutions you need — no matter the bacterium.

Resources:

“Listeria monocytogenes – How This Pathogen Survives in Food-Production Environments?“ Jacek Osek, Beata Lachtara and Kinga Wieczorek; Frontiers in Microbiology, 26 April 2022, NIH

“Introduction to the Microbiology of Food,” Texas A&M AgriLife Extension, College Station, Texas; accessed 25 March 2025.

“The Importance of Post-Construction Disinfection in Food Processing; Chlorine Dioxide Fumigation” Jay Parks, PureLine, accessed 27 March 2025