Effective use of disinfectants in a postharvest environment: a review

Sanitation is a critical aspect of the handling of fresh products, to minimize decay and risks from microbes of food safety concern, and disinfectants are the primary tools employed to accomplish this. An initial step in the development of a disinfectant application scheme is quantification of disinfectant potency to the organism of interest in vitro, where the level of mortality is defined by a concentration x time product (CT), which combines the concentration and the length of exposure where mortality occurs into a single value (e.g., mg-L-1-hours, ppm-minutes, etc.). For example, if a spore is inactivated by a CT of 100 mg L-1 min(-1), mortality would occur after 1 min with 100 ppm, 2 min with 50 ppm, and 4 min at 25 mg L-1, etc. CT values greatly facilitate the development of commercial practices and equipment. In the citrus industry, in vitro assays concluded that a sodium hypochlorite CT value of 400 mg L-1 min(-1) was effective to cause >99% mortality of conidia of Penicillium digitatum (cause of green mold) and arthrospores of Geotrichum citri-aurantii (cause of sour rot) at a solution pH of 10, although mortality was faster at lower pH. This knowledge enabled the use of hypochlorite to sanitize the relatively alkaline sodium bicarbonate solutions used to control postharvest decay. A second application of CT values is the expression of sulfur dioxide toxicity to Botrytis cinerea, cause of gray mold. Packages of table grapes are fumigated with sulfur dioxide, either applied externally or released from generator devices inside the packages. An issue for externally applied gas is to know if sufficient sulfur dioxide has diffused into the package. CT vales to control aerial mycelial growth and conidia germination were determined to be approximately 50 and 100 mu L L-1 h(-1), respectively, and a color change dosimeter was developed and enabled managers to know if sufficient gas had diffused into their packages. More recently, they were used to quantify gas released from generator devices inside the packages over long periods. Peracetic acid is another sanitation tool of renewed interest in California owing to approvals that allow higher rates of its use before harvest, acceptance by organic growers, and its compatibility with postharvest fungicides. Applied the day before harvest, peracetic acid reduced aerobic microbe and fungal populations by 1-2 log(10) units has been promising in near-harvest applications for table grapes and citrus fruit of peracetic acid for the control of postharvest decay.