Pathogen Can’t Hide From Biocides

Hypochlorous acid is effective against vegetative bacteria, but it has two huge drawbacks: disinfectant byproducts (reaction with organics) and corrosion. The off flavors created by chlorine, its reactions with organic molecules, and its impact on wastewater effluent treatment are strong negatives for many produce customers.

The reduced life span for produce processing equipment due to hypo-chlorite corrosion is also a major factor. In addition, hypochlorous acid, even within the optimal pH and temperature parameters, is not as effective a biocide against fungal and bacterial spores and protozoal cysts as are chlorine dioxide and ozone. Hypochlorite is still employed in many hydrocooler applications and in processing spray equipment, however, so it needs to be considered as a functional chemistry.

Peracetic Acid

PAA is effective as a direct food contact biocide because it breaks down into acetic acid and peroxide, substances generally recognized as safe. PAA has a number of advantages and disadvantages (See Table 1, left). As for regulatory approvals for PAA as a direct produce biocide, 40 CFR 180.1196 states that this biocide is exempt from the requirement of residue data when use solution is less than 100 parts per million (ppm). PAA has a wide variety of applications:

• Packing house sanitation at 85 ppm;
• Sanitizer for processing equipment such as peelers, slicers, and saws at 0.3-0.4 ounces/5 gallons water (85-123 ppm);
• Field equipment at 85 to 125 ppm; and
• Processing water treatment to control spoilage at 1 ounce/16 gallons of water (85 ppm).

Another biocide to consider is chlorine dioxide, which, after ozone, is the most powerful anti-microbe biocide available. Like other biocides, chlorine dioxide has several advantages and disadvantages (See Table 2, below). The most typical method of activation in food processing applications is the two-part system requiring acidification. There are a number of acids used to generate chlorine dioxide from its chlorite precursor.

Hydrochloric (HCl) acid is the most efficient acid activator. It is typically used in water treatment applications in which the activated product is diluted to a very low concentration. At higher use concentration levels, the excess chloride ion from the hydrochloric acid can create corrosion issues. Food-grade phosphoric acid is commonly used for many two-part activation or generation units. While not as efficient as HCl, it is more efficient than any other acid used. The only drawback occurs if you are using high concentration levels for certain approved applications: the excess phosphate could pose a problem to wastewater effluent.

A number of organic acids, including lactic and acetic, can be utilized to activate the chlorine dioxide precursor. Citric acid may be preferred in situations where you desire a low reaction level and where the citric acid helps in the appearance of sensitive produce products. They are all inefficient chemical reactions, however.

Chlorine dioxide precursors are various concentrations of tech grade sodium chlorite ranging from 7.5% up to 25% solutions. These solutions have an alkaline pH. Stabilized chlorine dioxide precursors are available, like the one manufactured by Bio-Cide International, Inc. (BCI; Norman, Okla.) These are buffered solutions of chlorite; the solution pH is far less alkaline than technical grade sodium chlorite.

These stabilized chlorine dioxide solutions are distinctly different in pH, especially when they are acidified to produce active, free chlorine dioxide solutions. There are a variety of safe, efficient generators to choose from. Two user-friendly units from BCI are a batch system for smaller applications called the Automatic Activation Non-Electric system and the continuous On-Line Activation System.

Safety Considerations

When using PAA and chlorine dioxide, you should remember that both products are strong oxidants; pay careful attention to the product data sheets and other information. Concentrated PAA can cause serious burns and inhalation discomfort. Use appropriate personal protective equipment when tubes are taken up. Manual dilution of the product is strongly discouraged; use a pump from Dosatron (Clearwater, Fla.) for auto dosing and dilution. Your best bet is to order a D116/ Di150 PVDF-H pump model that is oxidant compatible.