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Spring 2023
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Dairy Plant Biofilms and Their Control

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Dairy Plant Biofilms and Their Control

Contributed by Rick Heiman, DFA

Biofilms — what are they?

Biofilms are clusters of microorganisms attached to surfaces embedded in a self-produced matrix. While there are beneficial biofilms within the digestive tracts of warm-blooded mammals, such as in the cows that provide us the milk, and even in us humans, biofilm colonization of the plant environment regularly poses food safety and quality challenges for food and dairy processors.

While we may collect samples and use a laboratory to selectively culture for the presence of one type of organism for surveillance of our facility environments, biofilms rarely exist as a single species. Biofilms are usually a multi-species community of organisms in a symbiotic relationship benefitting from each other. Bacteria, yeasts and molds often form this thick, complex surface-attached community with water channels carrying dissolved oxygen and nutrients throughout the film.

How do biofilms develop in our food and dairy operations?

Biofilm growth conditions include incomplete removal of food soils in or on equipment, or in the plant environment. Ineffective sanitation may be caused by poor sanitary design or ineffective cleaning practices. Beyond pits, folds, cracks and inclusions, interfaces and non-self-draining equipment in the environment, hydrophilic surfaces, such as stainless steel, can also harbor biofilm.

Biofilms are cemented together by exopolymeric substances (EPS) containing polysaccharides resistant to removal. If soil is present on unclean surfaces for as little as 72 hours, a biofilm may develop; and if not removed, can reach structural maturity in as few as 10 days, becoming very difficult to penetrate and remove.

The microorganisms that form biofilms in our plants do not spontaneously generate to cause biofilms in our operations. They do not enter our plants through their own mobility. The microorganisms are introduced into our facilities and move around our plants via vectors.

Biofilms present food safety / quality risk and decrease operational efficiency.

Pathogenic bacteria, such as Listeria monocytogenes, Enteropathogenic E. coli. and Salmonella, are often found in mixed-culture biofilms. These organisms are a cause of a large number of foodborne illness and deaths annually.

In addition to pathogenic disease, biofilms are often implicated in spoilage incidents and shortened shelf life of products due to the shedding of spoilage bacteria from the films into products.

Biofilms may also create inefficiency or degradation of our assets in plant operations from accumulations in heat exchangers and corrosion of plant utilities.

How can biofilm development and inhabitation be prevented in operations?

The microorganisms that form biofilms in our plants do not spontaneously generate to cause biofilms in our operations. They do not enter our plants through their own mobility. The microorganisms are introduced into our facilities and move around our plants via vectors. The potential vectors are people (footways), raw materials, finished product distribution (wheelways), plant air make-up and gradient (pressured from high-care out to low-care and exhausted). We must utilize an effective hygienic zoning plan to control the vectors that bring microorganisms into our plant envelope and distribute them into low-care, medium-care and high-care environments from their origins outside the plant and lower-care environments.

Sanitation practices to stop biofilm development and inactivate for control

General plant control: Warehousing and storage areas should remain dry as much as possible. Zone-dedicated floor scrubbers may be used in the storage areas. The last application with the floor scrubber should be a residual sanitizer, such as a quaternary ammonium compound (QAC) solution at environmental strength.

Limit the amount of water used in the trafficways of the wet cleaned environment. Water used in walkways to include processing, liquid dairy ingredient areas, such as “silo alleys” and wet packaging areas, must be controlled. Avoid using water in the environment without a final application of environmental-strength sanitizer solution. Operations that occasionally need water for interdictive cleaning due to spills or packaging jams should use a prepared sanitizer solution from a central sanitize system for clean-up during processing, filling and closing. Water hoses should be removed from hose bibbs at production startup.

Ensure you practice an effective drain cleaning program with careful segregation and control of tools and containers. Surveil for pathogens with a robust EMP program. If you recover a pathogen in a drain, vector upstream three-dimensionally, inspecting ceiling, utilities, equipment framework in addition to floor areas for the source. Drains represent a collection point and generally represent less risk than the upstream source of the pathogens.

Wherever practical, modify existing wet or foam applications of sanitizer for walkways and wheelways to non-aqueous or the newer powdered technologies to include the powdered peroxide-based formulas.

Wet cleaned processing and packaging areas: Areas where processing is performed where water is used for cleaning usually present the most risk for biofilm development. A thoughtful SSOP should be developed to ensure complete removal of soils from these environments calling out hard-to-access (HTA) areas for cleaning and verification. These environmental areas (in addition to equipment verification) must also be included in the flashlight and stainless steel mirror inspection to verify sanitation effectiveness. An application of sanitizer should follow the post-rinse after cleaning. Foaming peracid sanitizers work very well to control outgrowth. A foaming QAC sanitizer is also effective if it is acceptable to have QAC in your effluent.

Wet cleaned processing, filling and closing equipment: Wet cleaned equipment should have the CIP or manual cleaning comply with an accompanying validated SSOP. If your SSOP is not validated, it will place more reliance on your verification step until you can validate your SSOPs.

If your equipment has a validated SSOP, you have established critical factors to verify to flow rate, chemical concentration, time and temperature. Using these critical factors each time you clean will ensure success. Verifications to ensure there is an absence of soil with a flashlight may require the beam to be held at an angle on some surfaces to visually verify clean. A stainless steel mirror is an excellent accompaniment to the flashlight to look under framework, motors, pumps, homogenizers, HPPs and other equipment. Residues left under equipment and framework are a common reservoir for biofilms in a plant environment. You must remove them each sanitation cycle to prevent a difficult, hardened biofilm and general biofilm issues that may move around the facility.

Powdered high-care packaging areas for RTE, infant formula, neutropenic foods: Whenever possible and as your infrastructure permits, move your packaging areas from wet cleaning to dry cleaning. This will significantly reduce pathogen recoveries. (See Dairy Foods, Dec. 2022, “Dry Cleaning for your Operations – Advantages and Challenges” for more information on hygienic design and practice for dry cleaning.)

Regimen to inactivate and remove developed biofilms

Literature suggests that biofilms allowed to establish themselves for a “period of time” may become “irreversible.” In the opinion of the author, irreversibility of the biofilm attached to a surface from the exopolysaccharides is subjective. This tends to be variable depending on the surface roughness, drainability and hygroscopicity of the area involved. Condition of plastics and elastomers is also a very important factor. Rubbers, plastics, and elastomers that are involved in recoveries of an undesirable organism should be replaced. All associated surfaces should be brought up to a high sanitary level to start the restoration of a positive finding.

Restoration cleaning procedure:

  1. Bring equipment and near environment up to a cleanable level for effective cleaning and sanitization. This may include restoration of surfaces for cleanability of the near environment and equipment for cleanability.
  2. Remove loose soils that remain.
  3. Pre-rinse.
  4. Apply a chlorinated alkaline cleaner and apply mechanical action with brushes or other mechanical means to loosen soils.
  5. Rinse.
  6. Apply a two-part biofilm inactivator, where part 1 contains hydrogen peroxide and QAC and part 2 contains activating carbonate salts and follow directions.
  7. Apply a foaming peracid sanitizer. Do not rinse.
  8. Pause for 24 hours.
  9. Re-apply foaming peracid sanitizer. Leave on for 1-2 hours and rinse.

Environmental monitoring should follow the restorativeclean to confirm the biofilm has been inactivated.

Prevention of biofilms in the plant are your key to success. Once biofilms are established, they can be difficult to control.

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