Before leafy green vegetables get to your local grocery store they are treated with sanitizers to reduce bacteria that have come in contact with the produce prior to or during harvesting and to prevent cross-contamination.
Chlorinated water is usually used in fresh produce industry. Chlorinated water treatment is cost-effective and easiest to manage among all of the Environmental Protection Agency (EPA) approved sanitizers for fresh produce. If the produce is dirty, it is rinsed first with cool water because organic material reduces the efficacy of the sanitation process.
Keep in mind this information is intended for small food processors. This sanitation process is not recommended for use at home to clean lettuce or other leafy vegetables from your garden, unless the chlorine meets food grade classification.
Chlorinated water is produced by adding either chlorine gas, calcium hypochlorite, or sodium hypochlorite to water. Sodium hypochlorite (NaOCl), also known as bleach, is sold in liquid form. Although more costly than other options, it is safer and relatively easy to use. Since minimal monitoring is required, NaOCl is a common chlorine source for chlorinated water in smaller scale operations. Sodium hypochlorite solution should be stored in a dark and dry place at temperatures between 50 and 70 degrees F and should be used within three months.
How is chlorinated water prepared?
Chlorinated water with a concentration range of 75 to 200 parts per million (ppm) active chlorine is commonly used. Active chlorine concentration of 200 ppm is the maximum amount allowed to be used by law. The chlorinated water solution with 200 ppm active chlorine is prepared by mixing approximately 1 tablespoon of 5.25% food-grade NaOCl solution, with 1 gallon of water. Although commercial household bleaches (such as Clorox) are sodium hypochlorite solution in water at 5.25% concentration, they may not be food grade. Food grade bleach is defined as sodium hypochlorite solution without any additives such as fragrances, stabilizers, or thickeners. Read the label because only food grade bleach is approved by the EPA for use in food processing.
Chlorinated water should be prepared fresh daily. Because chlorine content decreases with time, it should be monitored by using chlorine test strips or kits which measures the concentration of “free chlorine or available chlorine.”
How is chlorinated water applied?
Chlorinated water is applied by either submerging or spraying the fresh produce. Submerging involves loading produce into a long channel filled with cool, chlorinated water. Submersion for one minute, in a concentration of 75 to 200 ppm available chlorine, is usually effective. Spraying which also provides hydro-cooling is applied to the produce which is placed on a conveyor belt that simultaneously cools and sanitizes. For leafy greens, chlorinated water with available chlorine concentration of 75 to 150 ppm is used.
Why is pH of chlorinated water important for effective sanitation?
The effectiveness of chlorinated water is highly dependent on the pH of the solution.
The solution should be held between pH values of 6.5 to 7.5 to produce hypochlorous acid (HOCl). A pH below 6.5 is corrosive to processing equipment. A pH above 7.5 reduces the effectiveness of sanitation.
How is the pH of chlorinated water checked and adjusted?
The pH must be checked frequently so that adjustments can be made to offset the addition of the organic matter from the fresh produce. A pH meter should
be used, but pH test kits and even litmus paper can provide general pH ranges.
If the pH is found to be outside of the necessary range, sodium carbonate is added to raise the pH, and hydrochloric acid, vinegar or sodium bisulfate is added to lower the pH. A test kit is used to determine how much acid or base must be added to be within the desired range.
A more detailed fact sheet on this topic can be found on Ohioline (http://ohioline.osu.edu/factsheet/aex-262)
Gönül Kaletunç, Professor and food safety engineering specialist, can be reached at 614-292-0419, or email@example.com. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research & Development Center, and the College of Food, Agricultural and Environmental Sciences.