[ClO.sub.2] gas inactivates L. monocytogenes, Salmonella spp. on stainless steel, polyethylene surfaces.

Post-process contamination with L. monocytogenes and Salmonella in ready-to-eat (RTE) meat and poultry products has become a significant food safety concern. Biofilms formed by Listeria are a significant source of contamination that occurs even after surfaces are cleaned and sanitized.

Taiwanese scientists evaluated the use of chlorine dioxide ([CIO.sub.2]) gas as a sanitizing agent for L. monocytogenes, Salmonella and Listeria biofilms on stainless steel and polyethylene surfaces. They found that [CIO.sub.2] gas has great potential to minimize and eliminate selected pathogens on food contact surfaces.

Stainless steel and polyethylene strips were inoculated with about 7 log cfu per strip of five strains of L. monocytogenes or two strains of Salmonella. The strips were stored for 24 hours at 4 C and treated with 100 ppm to 320 ppm of [CIO.sub.2] gas for 10 minutes or 15 minutes at 22 C and 85% relative humidity.

The scientists enumerated Listeria and Salmonella by surface-plating on modified oxford agar and xylosel lysine desoxycholate citrate agar, respectively. Biofilms of L. monocytogenes Scott A on both types of strips were developed in diluted tryptic soy broth for two days at 25 C and then treated with 100 ppm to 2000 ppm of [CIO.sub.2] gas for 15 minutes to 30 minutes.

The researchers used an end-point technique to determine the complete inactivation of bacteria and biofilms. Any changes in the biofilms were visualized using scanning electronic microscopy (SEM). As [CIO.sub.2] gas and exposure time increased, log reductions of Listeria and Salmonella increased. A gas treatment of 150 ppm for 10 minutes provided a 1- to 2-log reduction of both bacteria on the two surfaces. As time increased to 20 minutes, both bacteria were eliminated.

Complete inactivation of Listeria occurred on both stainless steel and polyethylene surfaces when 220 ppm or more of [CIO.sub.2] gas was used for 10 minutes. Listeria bioflims, containing 6 log cfu per cm2 of cells, were eliminated under all the tested conditions. SEM studies showed that biofilms frequently grew on grooves and rough areas on the surfaces.

Further information. Kuo-Chan Tseng, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan; phone: [phone]; fax: [phone]; URL: www.ntu.edu.tw/eng2007. Richard Linton, Department of Food Science, Purdue University, 745 Agriculture Mall Dr., West Lafayette, IN 47907; phone: [phone]; fax: [phone]; email: [e-mail].