Chlorine dioxide cuts levels of pathogenic bacteria.

Contamination of fresh produce with pathogenic bacteria is a major concern in the food industry. Government agencies in the past have recommended at least a 2-log unit reduction from initial microbial counts on products.

The quest for the disinfectant that could replace chlorine has resulted in several possible candidates. Although no one disinfectant is perfect, chlorine dioxide is a very good alternative due to its characteristics. Chlorine dioxide can improve the microbiological safety of fresh fruits and vegetables. Like ozone and chlorine, chlorine dioxide is an oxidizing biocide and not a metabolic toxin. This means that chlorine dioxide kills microorganisms by disrupting the transport of nutrients across the cell wall, not by disrupting a metabolic process.

Scientists at North Carolina A&T State University evaluated the efficacy of chlorine dioxide alone or in combination with warm water in improving the microbiological quality of green leafy vegetables. It turns out that chlorine dioxide at 40 ppm is very effective in reducing pathogenic bacteria in green leafy vegetables.

Turnip green, spinach and mustard were submerged for 5 minutes in tap water, warm water at 45 C or 50 C, a chlorine dioxide solution at 20 ppm or 40 ppm, and in warm water followed by chlorine dioxide. Sample homogenates were analyzed for total bacterial counts of E. coli, S. typhimurium and S. aureus. Researchers monitored the degree of disinfection in terms of log microbial count reductions and the type of treatment used to obtain bacterial reductions.

Results indicated that tap water can remove 50% of the initial microbial loads. Both 45 C and 50 C warm water treatments can further reduce microbial loads. The activated chlorine dioxide aqueous solution at all concentrations most effectively inhibited microbial growth. There was no difference in disinfection rates between chlorine dioxide at 40 ppm alone and a combination of chlorine dioxide at 40 ppm and warm water. E. coli and S. typhimurium were more susceptible to inactivation by chlorine dioxide than was S. aureus.

Further information. Salam Ibrahim, Department of Human Environmental and Family Sciences, Food Microbiology and Safety Laboratory, North Carolina A&T State University, 171 Carver Hall, Greensboro, NC 27411; phone: [phone]; fax: [phone]; email: [e-mail].