Pathogen Can’t Hide From Biocides

Truck hydrocooling, used with field sweet corn, is the fourth method. The truck holds are designed with portable tanks containing crushed ice and cold water. Crates of produce are loaded, and portable perforated pipes above the product load shower it with cold water. The water is then collected, re-cooled, and recycled.

Other Cleaning Methods

Flumes in produce processing plants are often used to remove dirt and transport fruit and vegetables around the processing plant. This system, though highly efficient from a processing perspective, can cause a number of bacteriological problems due to the potential spread of contamination across a batch. A flume system will typically transport product from the initial sorting equipment to washing equipment and then, in some facilities, to a blancher. After the product is cooled and cut or chopped, depending on the facility, it may be transported via flume to de-watering equipment, like a basket centrifuge.

Due to organic loading, flume systems are prone to biofilm formation. Biocides like chlorine, peracetic acid (PAA), and chlorine dioxide are used for microbial control and process water reuse/recycling.

Spray washers are designed to remove the majority of the soil and attached debris from produce products. Equipment units like the one available from FMC FoodTech (Chicago) employ approved food-grade cleaners that apply a thin film prior to using chlorinated water and/or water treated with another biocide like chlorine, PAA, chlorine dioxide, or ozone.

There are typically four types of commercial washing equipment: flatbed brush washers, U-bed brush washers, rotary washers, and pressure washers. From a sanitation perspective, washers with brushes pose additional challenges, including getting proper cleaning while minimizing detergent retention and maintaining brush integrity and equipment life.

Whatever the cleaning method, all utilize biocides to reduce and control microbial levels on the produce and in the process water. The point of application determines whether the biocide label is controlled by the Environmental Protection Agency (EPA) or the FDA. If it involves raw agricultural commodities, as is the case with field hydrocoolers, the biocide must have an EPA label. Congress has specified that the EPA controls raw agricultural biocide usage in the field, and the EPA believes the intent is to treat the process water, not the product itself.

If the biocide used to treat the process water is employed in any further processing, including fresh cut, then the label is used for microbial control and must be consistent with FDA regulations. In either case, we are treating the process water for a dual purpose:

• To reduce contamination and bioburden in the process water in order to minimize microbial contamination and biofilm formation in the water stream and the equipment; and
• To treat the actual produce product to reduce/eliminate spoilage or pathogenic microbes on the consumed product.

Common Biocides

A wide variety of biocides and chemistries are used to treat processing water in the produce markets, including chlorine, PAA, chlorine dioxide, and ozone. While some processors still use actual chlorine gas cylinders to generate hypochlorous acid in solution, most don’t because of safety issues. Chlorine is the oldest, cheapest, and easiest of these four biocides to dose and control. However, it also needs to be in a fairly narrow pH range to be effective and safe. The truly safe range for biocidal hypochlorous acid from hypochlorite is from pH 6.5, where we achieve a 90% safety range, to pH 8.0, where we achieve a 20% safety range.

Chlorine can easily be dosed and controlled using either in-line or portable oxidation-reduction potential (ORP) probes. ORP needs to be kept in a functional range, from an optimum of 750 mV to a low of 350 mV. Time, temperature, and pH—along with exposure to direct sunlight—all factor into the ORP reading and the free hypochlorous acid you will have in your process water stream.