Chlorine compounds are widely used in the food industry to kill bacteria and disinfect. Examples include treating pasteurizer cooling water, washing fruit and vegetables and disinfecting food contact surfaces.

Use of Chlorine

Chlorine is usually combined with inorganic compounds, such as sodium or calcium, to produce hypochlorites, which are effective disinfectants. Chlorine mixed with sodium is a liquid bleach¹ known as sodium hypochlorite NaOCl. Chlorine mixed with calcium is usually in granular or tablet form and is called calcium hypochlorite - Ca(OCL)₂. Chlorine may also be available as chlorine dioxide (ClO₂). However, hypochlorites are the most active of the chlorine compounds. Table 1 lists these and other common chlorine sanitizer compounds.

• Factors affecting chlorine efficacy

• Storage of chlorine

• Preparing a chlorine solution

• Monitoring your chlorine solution

• Related links

• References

Table 1. Common chlorine sanitizer compounds

Factors affecting chlorine efficacy

Certain factors can affect the sanitizing power of chlorine compounds. They include the presence of organic material, pH, temperature, concentration, and contact time. When using chlorine as a sanitizer, note the following:
 

1. Presence of organic material. Organic material such as food residues decreases the effect of chlorine. For proper disinfection, use chlorine on cleaned surfaces only. Make sure you remove all organic material residue including fat and protein, before you apply chlorine as a sanitizer.
    

2. The pH of a chlorine solution. The level affects the antimicrobial activity. Use chlorine solutions with a pH range of 6.5 to 7.0 for optimum antimicrobial activity. At pH values near 4.0, hypochlorite solutions are most effective, but very unstable. At high pH values, the efficacy of chlorine is reduced.  If you are using a highly alkaline cleaner to remove protein and fat residues, rinse the surfaces thoroughly before applying chlorine solution because high pH residues will reduce the chlorine activity.
    

3. Temperature. Generally, chlorine antimicrobial activity increases with warmer temperatures. However, at high temperatures, chlorine compounds may release chlorine gas which is toxic. The potential of corrosion also increases as temperatures go up.
    

4. Concentration. Higher concentration of chlorine increases the effectiveness of killing micro organisms. However, high concentrations of chlorine are not recommended because they can cause corrosion, explosions, and adversely affect the health of workers. A chlorine concentration of 50 to 200 parts per million (ppm) is recommended to disinfect food contact surfaces including utensils, equipment, and tables.
    

5. Contact time. The bactericidal activity increases with longer exposure time. If the chlorine solution you are using does not exceed 200 ppm, no rinsing of the surface is required. If using a solution stronger than 200 ppm, rinse the surface with clean water after a few minutes of application. Do not let the chlorine solution stay in contact with equipment for more than 30 minutes or it could corrode.
    

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Storage of chlorine

Aqueous chlorine solutions such as commercial household bleaches are not stable. This means that chlorine may dissipate rapidly, reducing its content and effectiveness. So, chlorine powders should be used to sanitize in food processing plants, not bottled bleach.  

Preparing a chlorine solution

Hypochlorite liquid solutions commonly used in the food industry can be diluted with water until they reach the right concentration desired.

Example

To prepare 100 litres of a 50 ppm solution from a 12.5 per cent sodium hypochlorite (NaOCl), the following calculations are needed:

Final chlorine solution volume = 100 litres = 100,000 millilitres (ml), because a litre = one thousand millilitres

Final chlorine solution concentration desired = 50 ppm 

Initial chlorine solution concentration = 12.5% solution = 125,000/1,000,000 which can also be expressed as 125,000 parts per million (ppm) because 1 ppm = 1 ml in 1,000,000 ml

 Initial chlorine solution volume = Z

To prepare 100 litres of a 50 ppm solution of sodium hypochlorite, dilute 40 ml of a 12.5% sodium hypochlorite solution with water.

For more information on how to prepare a chlorine solution, visit the University of Auburn website at ag.auburn.edu/poul/virtuallibrary/mckeeeffectivechlorine.html
 

Monitoring your chlorine solution

Once you prepare your chlorine solution, use a test kit to monitor free available chlorine and in some cases, total residual chlorine (TRC) concentrations. Free available chlorine refers to the amount of chlorine available to react with bacteria. TRC is the amount of chlorine in the water, which includes chlorine available and chlorine bound with organic materials.  

Free and total residual chlorine test kits are commercially available including test strips, color cubes, titration-based test kits, colorimeters and colour discs. For more information on chlorine residual testing visit the Center for Disease Control and Prevention – SafeWater System (SWS) Project at cdc.gov/safewater/publications_pages/chlorineresidual.pdf

Related links

• Effect of chlorination on inactivating bacteria, viruses, and protozoa

• Chlorine Chemistry Council

References

Eifert, J.D., and Sanglay, G.C. 2002 Chemistry of chlorine sanitizers in food processing. Dairy, Food and Environmental Sanitation 22(7): 534-538.

¹Commercially, household bleaches such as Clorox™ and Javex are solutions of sodium hypochlorite in water at 5.25 per cent. This percentage refers to the concentration of sodium hypochlorite in the solution, which means that there are 5.25 grams of sodium hypochlorite in 94.75 grams of water
 

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For information on the Food Safety Program contact the CVO/Food Safety Knowledge Centre.  For technical information, call 204-795-7968 in Winnipeg; or e-mail foodsafety@gov.mb.ca. For general information, contact your local GO Centre.