Fresh produce washing aid, T-128, enhances inactivation of salmonella and pseudomonas biofilms on stainless steel in chlorinated wash solutions

Authors: SHEN, CANGLIANG - University Of Maryland; Luo, Yaguang - Sunny; Nou, Xiangwu; Bauchan, Gary; ZHOU, BIN - University Of Maryland; WANG, QIN - University Of Maryland; Millner, Patricia

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2012
Publication Date: 6/29/2012
Citation: Shen, C., Luo, Y., Nou, X., Bauchan, G.R., Zhou, B., Wang, Q., Millner, P.D. 2012. Fresh produce washing aid, T-128, enhances inactivation of salmonella and pseudomonas biofilms on stainless steel in chlorinated wash solutions. Applied and Environmental Microbiology. 78(19):6789-98.

Interpretive Summary: Chlorine is widely used in the fresh produce industry to reduce microbial populations on commodities, equipment, and contact surfaces as well as to prevent potential cross-contamination by foodborne illness pathogens during produce washing processes. However, the amount of sanitizing chlorine in solution is rapidily used up when the amount of organic material in the water increases substantially, such as occurs when large amounts of fresh-cut produce are suspended in wash solutions. Plant juices and organic materials released into wash water can lodge in crevices and on contact surfaces along with bacteria that can become attached firmly, and nearly invisibly. Such deposits can support growth of bacteria and formation of bacterial biofilm, which is a sticky matrix produced by bacterial cells. Bacterial biofilms are very difficult to control, because they are resistant to physical removal and to the sanitizing effects of chlorine in wash solutions. In this study, a new food-grade chemical mixture, T-128, formulated by scientists in the fresh produce industry, was evaluated for its effect on viability of bacterial biofilms formed by Salmonella, Pseudomonas, or both together, on stainless steel surfaces treated with chlorinated wash solutions in the presence of increasing organic loads. Results show that T-128 helps maintain sanitizing concentrations of free chlorine and significantly increases the biocidal effect of the sanitizing chlorine wash on Salmonella and Pseudomonas in bacterial biofilms on stainless steel even when increasing proportions of organic material are present in the washing water. Using T-128 in the fresh-cut produce processing environment shows promise as an aid in sanitizing surfaces by inactivating pathogenic or spoilage bacteria in biofilms on stainless steel, a common surface present on food-processing equipment.

Technical Abstract: The efficacy of chlorine wash solutions, with/without the washing aid, T-128, on inactivation of Salmonella and Pseudomonas populations in biofilms on stainless steel coupons was evaluated under conditions of increasing organic matter loads in the wash water. Biofilms were formed statically on stainless steel coupons suspended in 2 percent lettuce extract after inoculation with Salmonella enterica serovars Thompson or Newport, or Pseudomonas fluorescens. Coupons with biofilms were washed in chlorine solutions (0, 0.5, 1, 2, 5, 10, or 20 mg per L at pH 6.5, 5.0 and 2.9), with and without T-128, and with increasing loads of organic matter (0, 0.25, 0.5, 0.75, or 1.0 percent lettuce extract). Cell populations on coupons were dispersed using intermittent pulsed-ultrasonication and vortexing, and enumerated by colony counts on XLT-4 or Pseudomonas agars. Biofilm cell responses to fluorescent viability stains after treatment with washing solutions were examined using confocal laser-scanning microscopy. Results showed that 0.1 percent T-128 (without chlorine) reduced P. fluorescens biofilm populations by 2.5 log units, but did not reduce Salmonella populations. For both Salmonella and Pseudomonas, the sanitizing effect of free chlorine (1.0-5.0 mg per L) was enhanced (P less than 0.05) when combined with T-128. Application of T-128 decreased the free chlorine depletion rate caused by increasing organic matter in wash waters, and significantly (P less than 0.05) augmented inactivation of bacteria in biofilms compared to treatments without T-128. Image analysis of surfaces stained with SYTO 9 and propidium iodide fluorochromes corroborate the cultural assay results showing that T-128 can aid in reducing pathogen viability in biofilms, and thus can aid in sanitizing stainless steel contact surfaces during fresh-cut produce processing.