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Farm Food Safety: Choosing a Sanitizer for Washing Fresh Produce

The US Food and Drug Administration Produce Safety Rule (PSR) outlines the minimum food safety requirements for producers who grow, harvest, pack and hold fresh fruits and vegetables for human consumption (FDA, 2021). One of the key areas covered in the PSR is agricultural water.

Agricultural water is defined as water that contacts or is likely to contact the harvestable portion of ‘covered’ produce or food-contact surfaces (§112.3(c)).

“Post-wash and sanitized grapefruit exiting on conveyor belt”. Chad Carter, ©2012, Clemson University

“Post-wash and sanitized grapefruit exiting on conveyor belt”.
Chad Carter, ©2012, Clemson University

The PSR does not require that produce be washed before it is sold, but if producers decide to wash their produce before taking it to market, the PSR requires them to do a good job at it. The PSR states that if agriculture water is used to wash or cool covered produce, it must meet conditions outlined in the rule.

Two conditions that water must meet before a producer can use it to wash post-harvest fresh produce are:

  1. Be “safe and of adequate sanitary quality for the intended purpose” (§112.41) and
  2. Meet the performance standard of zero detectable generic Escherichia coli (E. coli) per 100 mL water (§112.44 (a)(2)).

There are several ways to maintain the quality of water during produce washing. These include adding clean water to the dump tank or washer during operation (with overflow) and emptying and refilling the dump tank or washer as necessary when the water gets too dirty or cloudy (high turbidity). Producers can also use a chemical sanitizer (also known as antimicrobial pesticides) in the wash water. Sanitizers such as chlorine, peracetic acid, ozone, and similar are important additions to wash water because they kill microorganisms that the water removes from the surfaces of fruits and vegetables during washing. Without the sanitizer, microorganisms in the wash water could reattach to the surfaces of fruits and vegetables as they pass through the immersion washer. It is important to understand the factors that affect a sanitizer’s ability to kill microorganisms to get the most “bang for your buck”.

Some of these factors will be discussed below.

Factors that affect how well a sanitizer works in produce wash water include incoming water quality (such as pH and mineral content), water temperature, amount of total dissolved solids in water (soil, dirt, debris), contact time with produce, and texture of the produce (smooth or rough surface).

There are over 4000 different sanitizers with 275 different active ingredients that are registered with the US Environmental Protection Agency (EPA) as antimicrobial pesticides. This long list can make it very difficult to select the sanitizer that works the best for you. The most common sanitizers used for fresh produce, along with some key references from other valuable sources, are listed below.

Chlorine

Chlorine is the most widely used sanitizer on the market. It has remained popular as a disinfectant for over 100 years primarily because it is effective, safe, easy to use, and inexpensive.

Chlorine purchased over-the-counter at a retail establishment such as a grocery store or big box store will contain between 5.25% and 8.25% sodium hypochlorite. If you are going to use over-the-counter bleach, it is important to buy the non-floral bleach that is labeled for use as a disinfectant for food. It is also important to make a note of the concentration of bleach in the bottle you are purchasing. In general, manufacturers are only required to label the concentration of bleach sold in retail stores if it contains more than 5.25% sodium hypochlorite. Industrial sodium hypochlorite can be purchased at concentrations ranging from 12 to 15%.

Chlorine is most effective when the water pH is between 6.0 and 7.5, and the water temperature is less than 86 F (30 C). For fresh produce, chlorine usage is recommended to be 50 to 200 mg/L (parts per million or ppm), at a pH below 8.0 with a contact time of 1 to 2 minutes (Parrish et al., 2003). Over-the-counter non-floral disinfectant bleach may be labeled with a recommendation of 25 ppm chlorine to sanitize food. It is important to follow the label on all of these products. It is also recommended that fresh produce treated with chlorine be washed with potable water after washing with chlorine to rinse off any leftover chlorine.

Chlorine is sensitive to pH, temperature, light, and organic material. At low pH (below pH 6.0) or high water temperatures, chlorine will gas-off into the air and become useless as a sanitizer. This means that it not only makes a bad odor, but it is no longer in the water and available to kill microorganisms in the wash water. Sunlight will cause chlorine to break down into oxygen and chlorate and become useless as a sanitizer.

There are some other sanitizers that are similar to bleach that may be used to wash fresh produce. Chlorine dioxide, acidified sodium chlorite (ASC), and electrolyzed water (acidified electrolyzed water) have to be made on-site before they can be used as a sanitizer. Chlorine dioxide can be used on fresh produce at levels not to exceed 3 ppm residual chlorine dioxide. Levels of electrolyzed water are the same as those recommended for traditional chlorine (50 ppm to 200 ppm). Overall, all three are more expensive than traditional chlorine.

Additional information on chlorine can be found in the fact sheet written by Dr. William McGlynn (2004) of Oklahoma State University (https://ucfoodsafety.ucdavis.edu/sites/g/files/dgvnsk7366/files/inline-files/26437.pdf) or in the article written by Dr. Trevor Suslow (https://www.siphidaho.org/env/pdf/Chlorination_of_fruits_and_veggies.PDF ).

Acidified sodium chlorate (ASC) can be used on fresh produce at concentrations between 500 to 1200 ppm at pH 2.3 to 2.9 (FDA, 2020. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=173.300 ).

Peracetic Acid (also known as Peroxyacetic Acid or PAA)

PAA has been used by the fresh produce industry since the 1950s. It is prepared by mixing hydrogen peroxide and acetic acid (vinegar). It has an advantage over hydrogen peroxide alone because it is less likely to be broken down by enzymes. Unlike chlorine, PAA retains its activity against microorganisms at high organic loads (soil, dirt, debris) but only at low pH (acidic pH). This means that it is important to monitor the water quality (cloudiness or turbidity) of wash water when using PAA. PAA is very effective at pH 3 to 7.5 and temperatures ranging from 32 F to 104 F (USDA-AMS, 2016). When used to wash fresh produce, PAA cannot go over 80 ppm or 80 mg/L. According to the FDA, fresh produce washed with PAA does not need to be rinsed with potable water before it can be sold. PAA breaks down pretty fast into carbon dioxide, water, and oxygen which makes it environmentally friendly, but it also means that it is important to check the amount of PAA in the wash water often.

PAA is typically sold under the trade names of Tsunami 100, Sanidate 5.0, StorOx, StorOx 2.0, OxiDate 2.0, and OxiDate 5.0 .

A guide on how to use PAA to wash fresh produce has been published by Cornell University and can be found using the following link https://rvpadmin.cce.cornell.edu/uploads/doc_676.pdf

Hydrogen Peroxide

Yes, the same hydrogen peroxide having a variety of uses, including eyewash, mouthwash, nasal spray, depending on the concentration used.

Hydrogen peroxide, also called hydrogen dioxide, can be used as a sanitizer of fruits and vegetables as a liquid or gas. It is considered to be “generally recognized as safe” or GRAS by FDA and EPA and is environmentally friendly because it breaks down to oxygen and water. It is affected by the organic load in the wash water but not by pH. The FDA has approved the use of hydrogen peroxide as a sanitizing solution on fresh produce at levels not to exceed 59 ppm. Recently, it has become more common to use hydrogen peroxide in combination with acetic acid (PAA) than to use it by itself.

Ozone

Ozone is a gas generated on-site from oxygen using a generator or electric charge. Ozone has a fresh, clean odor and can sometimes be present after a lightning storm, being generated by the electrical charge passing through the air. The electrical current separates some of the oxygen molecules which attach to O2 and create ozone gas (O). The ozone gas is typically bubbled into the water and used as a sanitizer solution, but it may also be applied to food as a gas.

Since ozone is not purchased as a liquid or powdered sanitizer, it cannot have an EPA registration number. However, the ozone generator is required to have an EPA establishment number on it. Ozone is considered “GRAS” by FDA and EPA; however, companies using ozone have to make sure that employees are protected from off-gassing. Occupational Safety and Health (OSHA) regulates employee exposure to ozone and sets an 8-hour permissible exposure limit at 0.1 ppm of air. To protect employees from ozone off-gassing, some companies install air filtration systems with ozone generators. Ozone is typically applied at a 2 to 10 ppm level in produce wash water for up to 5 minutes, but contact time can vary depending upon the commodity and cleanliness of the product going into the system.

Organic Acids

Organic acids, such as citric acid, acetic acid, lactic acid, and blends of these acids with phosphoric acid and sulfuric acid have been used as sanitizers for fresh produce. Organic acids are recognized as GRAS by FDA, but their usefulness against microorganisms is generally low and requires high concentrations for long periods of time.

Conclusion

Microorganisms that cause foodborne illness can be found on the surfaces of fresh produce. Produce can become contaminated with microorganisms from anything that it comes in contact with, including the environment, people, equipment, tools, and agricultural water. When added to water, sanitizers can reduce the likelihood that microorganisms in the water can spread to another surface (such as another fruit or vegetable or equipment surface). There are several options of sanitizers to consider, and this article discusses only a few of those options. When selecting a sanitizer that works best for your operations, make sure that the sanitizer is registered with EPA, is approved for direct use on fresh produce, and make sure you follow the label instructions for application. The label provides important information about allowable uses, efficacy against specific organisms, concentrations for use, rates of application, time of application, and need for drying or rinsing depending on the application. When handling any chemical, it is important to wear appropriate personal protective equipment.

Scientific articles cited in this article:

  1. Hadad, R. and A. Parr. 2018. How to wash produce using a peracetic acid solution. https://rvpadmin.cce.cornell.edu/uploads/doc_676.pdf
  2. Lawton, M, A. Kinchia, and L. McKeag. 2020. Produce wash water sanitizers: chlorine and PAA. https://ag.umass.edu/vegetable/fact-sheets/produce-wash-water-sanitizers-chlorine-paa
  3. McGlynn, W. 2004. Guidelines for using chlorine as a sanitizer in food processing operations. https://ucfoodsafety.ucdavis.edu/sites/g/files/dgvnsk7366/files/inline-files/26437.pdf
  4. Suslow, T. Chlorination in the production and postharvest handling of fruits and vegetables. https://www.siphidaho.org/env/pdf/Chlorination_of_fruits_and_veggies.PDF
  5. USDA-Agriculture Marketing Service. 2016. Peracetic Acid: Handling and Processing. Technical Bulletin. https://www.ams.usda.gov/sites/default/files/media/Peracetic%20Acid%20TR%203_3_2016%20Handling%20final.pdf

A List Of Common Antimicrobial Pesticides Or Sanitizers Used In Water That Contacts Raw Agriculture Commodities

Sanitizer Allowable Levels Advantages Disadvantages Followed by potable rinse Additional Comments
Chlorine 50 to 200 ppm

1 to 2 min contact time

Water pH 6.0-7.5

Cheap, easy to use, effective, can be bought over-the-counter (check the label) Corrosive to equipment (stainless steel, aluminum); degrades with age and exposure to sunlight and heat; does not work with high organic loads in water; pH dependent Yes Over-the-counter disinfectant chlorine (6%) is labeled for use on fresh produce at 25 ppm. Mix approximately 0.5 gallon of 6% chlorine per 1000 gallons water (EPA Reg. No. 5813-111)
Chlorine Dioxide Less than 3 ppm for fruits and vegetables that are not RAC; 1 ppm on peeled potatoes Less reactive than chlorine with organic load in water; effective at a wide range of pH Breaks down with exposure to sunlight; Has to be generated on-site before use; not as stable as chlorine; cost about twice as much as chlorine Yes
Acidified sodium chlorite 500 to 1200 ppm at pH 2.3 to 2.9 Better at killing microorganisms than chlorine because of low pH Generated on-site by blending before use Yes More research is needed on fresh produce. Low pH can cause some quality problems (discoloration of produce).
Peracetic Acid Less than 80 ppm when used on fruits and vegetables Noncorrosive to equipment; Works at a wide range of pH values and temperatures; Not as sensitive to organic load as chlorine. Cost more than chlorine; Vinegar odor; losses its effectiveness in the presence of metals (copper) No Store in a well-ventilated area
Hydrogen Peroxide Less than 59 ppm when blended with acetic acid and applied to fruits and vegetables that are not RAC Environmentally friendly. Declared GRAS2 by FDA. Higher concentrations can cause browning or bleaching in certain produce and can be corrosive and irritating. Unstable, degrades fast No Commercially available at 31-70% but 30-50% is most common. Dilute (3%) solutions are available to consumers.
Ozone No regulatory limit but typically used at 2-10 ppm for up to 5 min Declared GRAS by FDA. Environmentally friendly; Effective at low concentrations. Has to be generated on-site; unstable and highly reactive; Corrosive to equipment; OSHA requirements on employee exposure. No Solubility in water increases at lower temperatures and pH. Does not work as well at higher pH.
1Follow the label requirements on all antimicrobial pesticides or sanitizers and make sure they are registered with the Environmental Protection Agency before using them on raw agriculture commodities (RAC) or food.
2Generally recognized as safe.

Funding for this statement, publication, press release, etc. was made possible, in part, by the Food and Drug Administration through grant PAR-16-137. The views expressed in written materials or publications and by speakers and moderators do not necessarily reflect the official policies of the Department of Health and Human Services; nor does any mention of trade names,
commercial practices, or organization imply endorsement by the United States Government.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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