In the past few decades, the majority of foodborne outbreaks have been associated with contaminated fruits and vegetables. The last 7 years prior to 2018 saw more than 20 outbreaks coming from produce in North America alone. Some of the pathogens involved are Salmonella spp., Escherichia coli O157:H7, Listeria monocytogenes, hepatitis A, etc. Myriad produce types, such as cantaloupes, romaine lettuce, cucumbers, and even frozen produce, are responsible for these outbreaks. This year, the United States experienced a massive foodborne outbreak of E. coli O157:H7 in romaine lettuce. Although the recall is pretty much over, consumers, farmers, and retailers face a lot of repercussions. As of May 30, 2018, more than 150 individuals have become ill, and several have died. In addition, farmers have experienced extreme crop loss, retail sales have plummeted, and restaurants are changing suppliers and finding substitutes for romaine lettuce, which stops or slows down the supply chain flow.
Water Alone Is NOT Enough
In light of all these outbreaks, washing and rinsing the produce with water alone are not sufficient to eliminate pathogens. The solution to this issue is the use of disinfectants and sanitizers. Disinfectants and sanitizers are two different types of chemicals used in ensuring food safety. A sanitizer is used to reduce the number of bacteria on a surface to an acceptable level, whereas a disinfectant can eliminate a wider range of microorganisms. One cleaning agent cannot be effective against all pathogens, so it is important to know about multiple cleaning agents and how they work.
Factors Affecting Efficacy
Before discussing specific sanitizers and disinfectants, it is important to note that several different environmental factors can play into an antimicrobial’s efficacy:
• Potable Water: It is critical for the water to be potable and not contain any debris, odor, or microorganisms.
• Low Total Dissolved Solids (TDS): TDS are mineral deposits in water that can encourage the survival of pathogenic bacteria or bind to the bactericidal ingredients of a sanitizer. Because of this, it is better to use soft water instead of hard water. The presence of soil hinders the ability of a sanitizer to do its job, so getting rid of as much soil as possible is necessary for sanitation.
• Water Temperature: It is essential to maintain proper water temperature, because sanitizers typically do not work as well if the water is too cold. If the water is too hot, the sanitizer can vaporize and release toxic gas into the environment. Water temperature must also be considered in maintaining the quality of the produce. Different types of produce have different tolerance levels for water temperature.
• Water pH: Testing the water for pH is critical because sanitizers have different optimal pH values.
• Contact Time: In addition to temperature and pH, it is important to consider the contact time, because if a sanitizer or disinfectant is not applied long enough, sanitation will be insufficient. If a sanitizer is applied too long, it will be harder to clean off, may cause an off taste, and can cause a chemical hazard.
• Produce Surface Texture: Since sanitizers and disinfectants are usually applied to the surface, it is important to consider the surface texture. For example, a fruit with a lot of bruises or punctures will be much more difficult to clean than a fruit that is very smooth.
There are many other factors to consider, but these are the six most basic factors. Considering all these factors will help determine the right sanitizer or disinfectant to use on which fruit or vegetable and to kill a target pathogen.
Types of Disinfectants and Sanitizers
Specific sanitizers and disinfectants have unique characteristics that give them different functions and uses.
The most popular disinfectants are made with chlorine, which kills bacteria by disallowing uptake of nutrients and oxygen, which causes the denaturation of proteins.4 The chlorine-based sanitizers most commonly applied to fresh produce are pure chlorine gas, calcium hypochlorite, sodium hypochlorite, and chlorine dioxide. Chlorine-based sanitizers are easy to prepare, highly stable, fast acting, effective on vegetative cells, and rather cheap. However, chlorine can be very deadly if proper precautions are not taken.
Organic acids such as acetic, citric, and lactic acids can slow the production of energy, denature proteins, and cause cell lysis. These compounds are typically more natural ingredients on produce, cannot stain or release odors, and are noncorrosive to stainless steel. On the downside, organic acids do not work as well at killing yeasts, molds, and Gram-positive bacteria as other sanitizers.
Hydrogen peroxide causes cells to die through the alteration of osmotic pressure that leads to loss of cell wall integrity. This compound can kill spores, is cheap, is easy to prepare, and is fast acting. This chemical must be used with caution due to its instability in water, high allergenicity, and loss of effectiveness if not stored under the right conditions.
Peracetic acid’s bactericidal characteristics include disorganization of cell structure through degradation of the cell membrane’s lipids and proteins, as well as cell lysis. This chemical has been shown to kill bacterial spores, is effective in a neutral pH environment, and is mostly noncorrosive. Unfortunately, this compound can corrode if exposed to skin or high temperatures, has an uncomfortable aroma, and becomes less effective in the presence of metals.
UV light, a more natural disinfectant, can be applied to fresh produce to damage a cell’s genetic material. UV light is also cheap, eliminates a wide variety of pathogens, and gives off little-to-no heat to maintain freshness. This form of radiant energy works on all fresh produce except for lettuce, as it can destroy this vegetable’s quality.
Aqueous ozone, a natural, new alternative sanitizer, does an excellent job of mitigating the growth of bacteria, molds, protozoa, and viruses. This compound does not require a large concentration and is extremely environmentally friendly, given that this world is composed of ozone. Ozone has been shown to be effective on many varieties of fruits and vegetables.
No matter what sanitizer one decides to use, one or more parameters will have to be monitored. These parameters may include, but are not limited to, temperature, time, pH, water quality, and concentration. For example, one may use chlorine, which “is most effective…at a pH between 6.0 and 7.5” and a concentration of 200 ppm for sanitizing the actual produce. When constructing a written monitoring procedure, it is important to include the individual responsible, the method of cleaning and sanitizing, the frequencies at which cleaning and sanitizing are performed, and the product or area that needs to be cleaned. A monitoring log should have places to record date, time, initials, test results, whether the results are acceptable or unacceptable, and where the monitoring was applied. If test results are not acceptable, corrective action must be taken according to the manufacturer’s guide.
Why Are There Still Foodborne Illness Outbreaks Associated with Fresh Produce?
Many processors are using the right sanitizer and/or disinfectants the right way, conducting in-plant processing validation studies, and have verification and monitoring procedures that are stellar; they may still have foodborne illness outbreaks (see “Validation and Verification Procedures”). A recent study from the University of Southampton may address this conundrum. Chlorine used to decontaminate fresh produce could be ineffective, because it may mask pathogens present on the fresh produce, making them undetectable. The study states findings that using as little as 3 ppm chlorine as a sanitizer causes pathogens (specifically L. monocytogenes) to enter a viable-but-nonculturable (VBNC) state. When in a VBNC state, the pathogen cannot be cultured using standard laboratory culture techniques. This study looked specifically at Salmonella and L. monocytogenes in fresh leafy greens. This study brings to light the reality that traditional and new innovative pathogen testing methods must be examined using the VBNC state of several pathogens.
Consumer food trends are adding more fresh fruits and vegetables to daily diets. It is important for produce to be safe and delicious to benefit human health and sustain life. It is the responsibility of everyone in the farm to fork continuum to diligently make fresh produce safe for consumption. Disinfectants and sanitizers have a key role to play in ensuring produce safety.
Gina R. (Nicholson) Kramer, RS/REHS, is the executive director of Savour Food Safety International.
Megan Doran is an Ohio State University student and summer intern at Savour Food Safety International. She will graduate in December 2018 with a B.Sc. in agriculture, food business management.