Food Safety and Environmental Services
Food Equipment Cleaning and Sanitizing: Water Chemistry and Quality (Page 4)
Chlorine, in its various forms, is the most commonly used sanitizer in food processing and handling applications. Commonly used chlorine compounds include: liquid chlorine, hypochlorites, inorganic chloramines, and organic chloramines. Chlorine-based sanitizers form hypochlorous acid (HOCl, the most active form) in solution. Available chlorine (the amount of HOCl present) is a function of pH. At pH 5, nearly all is in the form of HOCl. At pH 7.0, approximately 75% is HOCl. The maximum allowable level for no-rinse applications is 200ppm available chlorine, but recommended usage levels vary. For hypochlorites, an exposure time of 1 min at a minimum concentration of 50ppm and a temperature of 24°C (75°F) is recommended. For each 10°C (18°F) drop in temperature, a doubling of exposure time is recommended. For chloramines, 200ppm for 1 min is recommended.
Chlorine compounds are broad spectrum germicides which act on microbial membranes, inhibit cellular enzymes involved in glucose metabolism, have a lethal effect on DNA, and oxidize cellular protein. Chlorine has activity at low temperature, is relatively cheap, and leaves minimal residue or film on surfaces.
The activity of chlorine is dramatically affected by such factors as pH, temperature, and organic load. However, chlorine is less affected by water hardness when compared to other sanitizers (especially the quaternary ammonium compounds).
The major disadvantage to chlorine compound is corrosiveness to many metal surfaces (especially at higher temperatures). Health and safety concerns can occur due to skin irritation and mucous membrane damage in confined areas. At low pH (below 4.0), deadly Cl2 (mustard gas) can form. In recent years, concerns have also been raised about the use of chlorine as a drinking water disinfectant and as an antimicrobial with direct food contact (meat, poultry and shellfish). This concern is based upon the involvement of chlorine in the formation of potentially carcinogenic trihalomethanes (THMs) under appropriate conditions. While chlorine's benefits as a sanitizer far outweigh these risks, it is under scrutiny.
Chlorine dioxide (ClO2) is currently being considered as a replacement for chlorine, since it appears to be more environmentally friendly. Stabilized ClO2 has FDA approval for most applications in sanitizing equipment or for use as a foam for environmental and non-food contact surfaces. Approval has also been granted for use in flume waters in fruits and vegetable operations and in poultry process waters. ClO2 has 2.5 times the oxidizing power of chlorine and, thus, less chemical is required. Typical use concentrations range from 1 to 10ppm.
CLO2s primary disadvantages are worker safety and toxicity. Its highly concentrated gases can be explosive and exposure risks to workers is higher than that for chlorine. Its rapid decomposition in the presence of light, or at temperatures greater than 50°C (122°F) makes on-site generation a recommended practice.
Use of iodine as an antimicrobial agents dates back to the 1800s. This sanitizer exists in many forms and usually exists with a surfactant as a carrier. These mixtures are termed iodophors. The most active agent is the dissociated free iodine (also less stable). This form is most prevalent at low pH. The amount of dissociation from the surfactant is dependent upon the type of surfactant. Iodine solubility is very limited in water. Generally recommended usage for iodophors is 12.5 to 25ppm for 1 min.
It is generally thought that the bactericidal activity of iodine is through direct halogenation of proteins. More recent theories have centered upon cell wall damage and destruction of microbial enzyme activity.
Iodophors, like chlorine compounds, have a very broad spectrum: being active against bacteria, viruses, yeasts, molds, fungi, and protozoans. Iodine is highly temperature-dependent and vaporizes at 120°F. Thus, it is limited to lower temperature applications. The degree to which iodophors are affected by environmental factors is highly dependant upon properties of the surfactant used in the formulation. Iodophors are generally less affected by organic matter and water hardness than chlorine. However, loss of activity is pronounced at high pH.
Iodine has a long history of use in wound treatment. However, ingestion of iodine gas does pose a toxicity risk in closed environments. The primary disadvantage is that iodine can cause staining on some surfaces (especially plastics).
Food Equipment Cleaning and Sanitizing Continued: Water Chemistry and Quality Page 5