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The Chemistry of Chlorine Sanitizers Chlorine compounds
are the most commonly used sanitizers in food plants. They are effective
against virtually all bacteria and are relatively easy to prepare and
apply. Because these compounds are so often used, this article is
intended to provide a thorough understanding of the chemistry of chlorine
so that sanitizing activity can be maximized.
Chlorine is often found in nature, but not as a free element. To be used, chlorine must be separated from other elements via electrolysis. This process uses an electrical current to break down salt water into its basic components. The chlorine gas that is produced is dried, chilled and pressurized or it is converted into a liquid. When chlorine gas is added to water, hypochlorous acid is produced. It is the most effective antimicrobial form of chlorine. Chlorine as a Sanitizer The dairy industry was the first of the food industries to use chlorine for antimicrobial purposes. Today chlorine is used for the purification of potable water used in dairy processes and for disinfection of equipment, pipelines, surfaces and hands. Several types of chlorine compounds are used as sanitizers. They include liquid chlorine, hypochlorites, acidified sodium chlorite, inorganic and organic chloramines, and sodium dioxide. All chlorine products form hypochlorous acid in solution. The rate at which gaseous chlorine, hypochlorites, and chloramines kill bacteria is directly related to the amount of free chlorine (hypochlorous acid) in the water. The effectiveness of any chemical or process intended to destroy microorganisms depends upon several factors, as discussed on the Microbiology Highlights page. Chlorine compounds are no exception. They are rather sensitive to factors such as pH, temperature, concentration, duration of exposure, and presence of organic matter. Antimicrobial activity of a chlorine based sanitizer is greatly affected by pH. For example, the hypochlorous acid in solution increases or decreases with pH. As pH increases , dissociation occurs to create hypochlorite ions and hydrogen ions, making the solution less effective against microbes. However, if the pH falls below 4.0, dangerous chlorine gas is produced. The optimum pH for the presence of hypochlorous acid is 6.5 to 7.0. However, it is not advisable to adjust the pH to a specific value, many chlorine sanitizers are formulated at a high pH level to extend storage life. Chlorine dioxide is not as affected by pH and is effective at even high pH levels. Temperature is another factor that affects chlorine effectiveness. For chlorine and other chemicals, reaction rates double for every 10 C increase in temperature, up to 52 C. Yet, as temperatures rise and pH decreases, equipment corrosion is more likely to occur. Concentration and duration of exposure are also important considerations. As concentrations and contact time increase, generally antimicrobial effectiveness does as well. However, limits must be placed on both factors. Chlorine concentrations cannot exceed a certain point or they are unsafe and undesirable to use in the food processing environment. Not only can high levels of chlorine affect odor, flavor, and color of products, but it can be hazardous to workers' health. High concentrations are needed only when treating water that may contain a high number of microorganisms and oxidizing compounds which would render a smaller concentration ineffective. An exposure time of a few seconds to just over one minute should be sufficient. If exposure exceeds a few minutes, corrosion of metal is more likely to occur. A final factor that has a major impact on chlorine sanitizer effectiveness is the presence of organic material. The presence of soils, fats, proteins, and other organic compounds will inactivate chlorine as an antimicrobial. All surfaces should be cleaned so that no residual organic material remains. Due to the sensitivity of chlorine sanitizers to such factors, the level of free chlorine in solution should be monitored. Free chlorine is the amount of excess chlorine that has not reacted with organic materials and bacteria. Free chlorine concentrations of less than 3 parts per million are effective against microbes. All those involved in food production should have knowledge of the sanitizers used in the facility. If one can maximize the effectiveness of chlorine then waste and hazardous situations can be avoided. References
Eifert, Joseph D., Gabriel C Sanglay. "Chemistry of Chlorine Sanitizers in Food Processing" Dairy, Food, and Environmental Sanitation 22:534-538. McLaren, Dave. "The Use of Chlorine-based Sanitizers in Food Processing Facilities." Water Quality and Health Newsletter Summer 2001. |
