Adapted from: Silva, E. 2008. Approved chemicals for use in organic postharvest systems. In Wholesale success: a farmer's guide to selling, postharvest handling, and packing produce (Midwest edition). Available online at: http://www.familyfarmed.org/wholesale-success/ (verified 6 Dec 2011).
The USDA has established a National Organic Program (NOP) Rule to set and enforce uniform standards for both producing and handling agricultural and processed food products labeled as organic. Chemicals used in organic postharvest operations must comply with the NOP rules. Most synthetic inputs are prohibited; those that are allowed may be used only with restrictions. For more information, see the related articles National Organic Program: What Agricultural Professionals Need to Know and Can I Use This Input on my Organic Farm?
Adequate sanitation and disinfection during postharvest processes are vital components of a postharvest management plan. As food safety regulations become increasingly important to the sales and marketing of crops, the establishment of proper measures to ensure the elimination of food-borne pathogens is essential. In addition to mitigating potential food-borne illness, proper sanitation during postharvest handling can also minimize the occurrence of postharvest disease and decay. As is the case during the production stage of the crop, all products used during the postharvest period must adhere to NOP regulations.
Chlorine is a very common disinfectant that can be added to transport flumes or to produce cooling or wash water. Liquid sodium hypochlorite is typically used, with the pH of the water maintained between 6.5 and 7.5 to optimize effectiveness (Suslow, undated). The NOP approves chlorine’s use (calcium hypochlorite, chlorine dioxide, and sodium hypochlorite) in postharvest management as an algicide, disinfectant, and sanitizer. These regulations restrict the residual chlorine levels in the water at the discharge or effluent point to the maximum residual disinfectant limit under the Safe Drinking Water Act, currently established by the Environmental Protection Agency (EPA) at 4 mg/L (ppm) for chlorine. However, the levels of chlorine used to prepare water to be used for sanitation of tools, equipment, product, or food contact surfaces may be higher than 4 mg/L and should be in high enough concentration to control microbial contaminants. Thus, the concentration of chlorine at the beginning of a disinfection treatment is generally greater than 4 mg/L; however, care must be taken to ensure that the effluent water does not exceed this limit. For more information, read the NOP's Guidance, "The Use of Chlorine Materials in Organic Produciton and Handling."
Chlorine can exist in water in various forms. Free chlorine may be found as hypochlorous acid and hypochlorite ion, with the hypochlorous acid form providing the strongest antimicrobial properties. At a pH of 6.5, 95% of the chlorine is in the hypochlorous form; maintaining the water pH at this range provides the greatest disinfecting power. Chlorine may become bound to soil, debris, and other organic matter in the water; once chlorine becomes combined with these materials, it is no longer available for disinfection. In order to maximize the effectiveness of any chlorine treatment, it is beneficial to perform additional cleaning steps to produce arriving from the field. This may include a vigorous prewash with brushes or sponges to remove excess debris from the produce, or a clear water rinse to remove soil and other debris, prior to using the sanitizer solution. Also, cleaning out dump tanks and residue screens will help minimize the presence of soil and debris and maximize chlorine’s effectiveness.
Ozone is becoming an increasingly popular alternative to chlorine for water disinfection. Ozone, through its action as an oxidizer, provides comparable disinfection power to chlorine, rapidly attacks bacterial cell walls and thick-walled spores of plant pathogens. Ozone treatments have the benefit of forming fewer undesirable by-products than chlorine treatments, such as trihalomethane, chloroform, and other dangerous compounds. Ozone is faster acting than chlorine and allows for adequate disinfection with short-term contact to the produce. The use of ozone does require a greater capital investment and ongoing operating costs than the use of chlorine, however. Because of the instability of the compound (20 min in clean water), ozone must be generated on-site, requiring investment in ozone-generating equipment. These generators create ozone through the action of a high energy source (UV light or corona discharge), splitting oxygen molecules that then recombine to form ozone. Small-scale ozone generating units are available for a few thousand dollars.
Peroxyacetic acid (PAA, also called peracetic acid on the NOP National List), in combination with hydrogen peroxide, is another popular alternative to chlorine that is allowed in organic production. Like chlorine, PAA performs well in water dump tanks and water flumes. Like ozone, PAA treatments result in safer byproducts than chlorine treatments. The disinfection performance of PAA is comparable to chlorine and ozone. To maximize effectiveness, PAA should be maintained at a level of 80 ppm in the wash water. A post-treatment wash with clean water is required after a disinfection treatment with PAA.
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.