The Efficient Use of Chlorine and Other Sanitizers in Postharvest Fruit and Vegetable Operations

by Shari L. Plimpton, Ph.D.

The use of sanitizers such as chlorine is an important part of postharvest handling and preparation of fresh fruits and vegetables. For reasons of product quality, cost, and worker safety, it is therefore important that the grower understand how to use sanitizers efficiently.

In order to efficiently use these important substances, one must first understand the role that they play. Clean, disinfected water minimizes the transmission of pathogens from water to produce, or from infected to healthy produce, either within a lot or from lot to lot. Plant surface contours and cuts can introduce pathogens into the fruit, and provide growth opportunities for them. It is essential that a sufficient quantity of sanitizer be available to kill these pathogenic microbes before they find a home on or in the produce. To ensure this availability, the following facts are important to remember.

Pre-harvest practices
Excessive use of chlorine (or other sanitizers) has negative effects on product quality. As harvest approaches, therefore, the microbial standards used for water should increase gradually to minimize infestation and potential contamination.

Water
Potable water should be used for all postharvest activities, including washing, grading, material handling (fluming), and cooling. Sanitizers do not easily kill some pathogens that are harmful to humans, so clean potable water is the best preventative step available. When quality is in doubt, a certified analytical lab should perform a water quality evaluation.

Organic Matter
The power of chlorine and other sanitizers to kill pathogens is because they are powerful oxidizers, and highly reactive. Unfortunately, they do not discriminate what they react with. Reacting with both organics and inorganics in wash water rapidly uses up chlorine in particular. Care should be taken to filter out soil, leaves, and other debris, and to periodically change water as it becomes full of exudates such as sap from cut or scuffed produce.

Performance Enhancers
Sanitizers will only kill what they contact. Water films that form on small surface contours may prevent contact with target microorganisms. Surfactants decrease water surface tension, and in effect, "make water wetter" by allowing freer flow and can make chlorine and other sanitizers more effective. Examples of approved materials are polysorbate 80 and Chlorine Potentiator from Bonagra Technologies, Inc.

Temperature
Sanitizers such as chlorine tend to be more active as temperatures increase, but in general, the need for cooling from water is more important than the slight increase in performance from higher temperatures.

pH
As those with home swimming pools realize, the performance of chlorine is affected by he pH (acidity/alkalinity) of the water. This is because chlorinated water actually has three components; chlorine gas, hypochlorous acid (HOCL), and hypochlorite ions. Of these, HOCL is the most effective and desirable as a bactericide, and is the one, which varies the most with changes in the pH. In general, a pH of 6.5-7.5 produces the optimum balance of activity, stability, and safety (at low, or acidic pH’s, chlorine gas is actually released from water.) pH should be frequently if not continuously monitored. Both chlorine and pH can and should be monitored using test paper strips, colorimetric kits, or electronic sensors. Muriatic (HCL) or citric (C₆H₈O₇) are commonly used to keep pH within the proper range.

Concentration
The optimum sanitizer concentration and dwell time varies from product to product, but exposure time of 3-5 minutes in a solution with a sanitizer concentration of 50 to 75 parts per million in a solution of slightly acidic (6.5 pH) is generally viewed as adequate. Caution must be used, however, as some products will lose color or develop surface defects when levels are too high or exposure times too long. Most extension offices can provide data on specific crops.

Proper and efficient use of sanitizers will maximize the benefits of the substances to product safety and quality, while minimizing the expense and risks associated with them.

Consultation for GAPs, developing food safety programs, and passing third party audits is available through CIFT. You can reach us by calling Shari L. Plimpton at 614-314-4627 or emailing us at foodsafety@eisc.org.

Good Agricultural Practices Articles...

• ABCs of GAPs

• Cleanliness is Next to Food Safety

• The Distant Sound of Drumming

• The Efficient Use of Chlorine and Other Sanitizers in Postharvest Fruit and Vegetable Operations

• The Elements of Produce Food Safety Programs

• GAPs in Organics: Fresh Produce Safety from Pre-planting through Production

• Handling Your Food Safety Risks

• Its Not All in the Bag

• Passing a Third Party Food Safety Audit

• Pest Patrol for Fruit and Vegetable Growers

• Planning for Prevention: Fresh Produce Safety from Pre-planting through Production

• So, Just How Clean is Your Water

• Sustaining Healthy Soil

• The Value of a Food Safety Plan

• Water, Water Everywhere

• Worker Hygiene Keeps Produce Clean