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Sanitizer in produce wash water - can it improve shelf life of greens?

Annalisa Hultberg Extension Educator, food safety 

While not all produce should be washed during postharvest handling, many items need to be washed to remove soil or to hydrocool to remove field heat from product. It is a best practice use a sanitizer in bulk tanks of wash water to reduce the potential to spread contamination via the water. But can sanitizer also improve the shelf life of produce? We are conducting trials this summer to see.

Many farmers note that their produce lasts longer when it is rinsed in water with a sanitizer, but we don't have documentation about the impact of sanitizers on shelf life. The food safety outreach team is conducting trials to see if leafy greens last longer when rinsed in two types of sanitizers vs a rinse in plain water.

We know that sanitizers are very effective at inactivating bacteria such as Salmonella and Escherichia coli O157:H7 that may be present in the water and brought in from the field, hands, compost or other sources. The hypothesis is that the two treatments (Sanidate 5.0 peroxyacetic acid based sanitzer and 5.5% sodium hypochlorite bleach) will improve shelf life of the  greens over a plain water rinse. This is because the sanitizing agents inactivate bacteria, viruses, spores, fungi and other microorganisms that can lead to degradation of fresh produce in storage.  

Stay tuned for results in early fall. We will be taking photos and measuring degradation of greens in storage and keeping track of other metrics like temperature in different zones of the cooler to control for variables. 

Read below for instructions on using sanitizer in wash water. If you are looking for an organically approved sanitizer for postharvest wash water, many growers use Sanidate 5.0 from BioSafe systems. You can find it at Johnny's or order it from Arbico Organics. Sanidate 5.0 breaks down in the environment into oxygen, water and carbon dioxide. Or, you can use plain, unscented bleach that is labeled for use in sanitizing fruit and vegetable wash. Both are used at very low concentrations. Always read the label to determine the rate and which to use sanitizers and measure PPMs to ensure you have not used too much.

Here is an overview on using sanitizers in produce wash water. 

Step 1. Remove soil and organic matter from produce before washing

Lightly brush produce with thick skins or rinds (melons, potatoes, carrots) or prewash in plain water (leafy greens). Organic matter, such as dirt and other debris, reacts with the sanitizer solution to lower its effective concentration. The more organic matter in a water and sanitizer solution, the less effective the sanitizer is (especially chlorine - based sanitizers).

Step 2. Measure and mix solution for rinsing

Water used for washing must be clean and potable (drinkable). Add the amount of sanitizer as indicated by the label to reach the PPM for fresh fruits and vegetables. 

Water should be at a cool temperature, but not cold. If it is too cold the sanitizer will not be effective; if it is too warm it may encourage the growth of some pathogens and disease.  Check the label of the sanitizer for effective temperature range.

If using household chlorine, use only plain, unscented household bleach without added thickeners or fragrances.

Step 3. Rinse products in solution

Be very gentle with leafy greens and other items. Let the water remove the dirt, not your hands. Do not immerse tomatoes.

Step 4. Rinse products in fresh water if indicated by the label

Read the label carefully. Some sanitizers require a freshwater rinse, others do not.

Step 5. Change water frequently

Used wash water can be poured onto non-edible crops, grasses or shrubs if you don’t have a drain. Make sure to change the water when it becomes dirty and when a new crop is added. After dumping old water, refill the container with clean water, re-measure the sanitizer, and test for concentration.

Step 6. Monitor pH and sanitizer levels

To maintain levels that are appropriate for your sanitizer, use test strips or another method to verify the concentration after each addition of sanitizer. 

Other sanitizers will vary - follow the instructions on the package.  pH level should be maintained between 6.0 and 7.0 to provide for the greatest effectiveness. 

Step 7. Always document the sanitizer levels on a log sheet

Keep a log sheet with the date, time, and concentration levels near your washing station. You should check the sanitizer level in the water after each addition of sanitizer and document the level on the log sheet.

For more information: 

UMN Extension page on using produce wash water sanitizers

Produce Wash Water Sanitizers: Chlorine and PAA (UMASS Amherst)

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