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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.
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.
Table 1. Common chlorine sanitizer compounds
|sodium hypochlorite ~5% active chlorine||hypochlorous acid, sodium oxychloride, bleach|
|sodium hypochlorite ~10-15% active chlorine||hypochlorous acid, sodium oxychloride|
|calcium hypochlorite||hypochlorous acid, calcium oxychloride|
|sodium dichloroisocyanurate||Dichloro-s-triazine-2,4,6-trione; sodium salt|
|chlorine dioxide||chlorine oxide, chlorine peroxide|
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:
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.
Hypochlorite liquid solutions commonly used in the food industry can be diluted with water until they reach the right concentration desired.
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
Initial chlorine solution concentration x Initial chlorine solution volume = Final chlorine solution volume x Final chlorine solution concentration desired
125,000 ppm x Z = 100,000 ml x 50 ppm
Z = 40 ml
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 www.ag.auburn.edu/~curtipa/virtuallibrary/mckeeeffectivechlorine.html
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
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
For more information, email the CVO/Food Safety Knowledge Centre or call 204-795-8414 in Winnipeg.