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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE Title: Whole-leaf sanitizing wash improves chlorine efficacy for microbial reduction and prevents pathogen cross contamination during fresh-cut lettuce processing

Authors
item Nou, Xiangwu
item Luo, Yaguang

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2010
Publication Date: July 9, 2010
Citation: Nou, X., Luo, Y. 2010. Whole-leaf sanitizing wash improves microbial reduction efficacy and prevents pathogen cross contamination during fresh-cut lettuce processing. Journal of Food Science. 75(5):M283-M290.

Interpretive Summary: Fresh and fresh-cut leafy greens have been implicated in a number of outbreaks of foodborne infections caused by E. coli O157:H7 and other bacterial pathogens. Currently, nearly all fresh-cut lettuce processing facilities in the United States use chlorinated water or other sanitizer solutions for microbial reduction after lettuce is cut. However, organic materials released from the cut edges deplete chlorine and reduce its efficacy on pathogen reduction. Furthermore, localized pathogens can be spread out to other clean products during washing unless sufficient sanitizer levels are maintained. In this study, we demonstrated that chlorine efficacy for pathogen reduction can be significantly improved by applying the sanitizing wash prior to cutting. Sanitizing wash prior to cutting also significantly reduced the occurrence of cross contamination of bacterial pathogens during fresh-cut processing. Therefore, we propose that instituting a sanitizing wash could be a practical means for improving pathogen reductions during fresh-cut processing. This research is useful for food scientists, engineers, regulatory government agencies, and the fresh-cut leafy greens industry.

Technical Abstract: Currently, nearly all fresh-cut lettuce processing facilities in the United States use chlorinated water or other sanitizer solutions for microbial reduction after lettuce is cut. It is believed that freshly cut lettuce releases significant amounts of organic matters that negatively impact the effectiveness of chlorine or other sanitizers for microbial reduction. The objective of this study is to evaluate whether a sanitizer washing prior to cutting would improve microbial reduction efficacy in comparison with traditional post-cutting sanitizer washing. Romaine lettuce whole leaves were quantitatively inoculated with E. coli O157:H7 strains and washed in chlorinated water before or after cutting, and E. coli O157:H7 cells that survived the washing process were enumerated to determine the effectiveness of microbial reduction for the two cutting-washing sequences. Whole-leaf washing in chlorinated water improved pathogen reduction by approximately one log unit. Similar improvement in the reduction of background microbial flora was also observed. Inoculated 'Lollo Rossa' red-leaf lettuce leaves were mixed with non-inoculated green-leaf lettuce leaves to evaluate pathogen cross contamination during processing. High level (96.7 percent sub-samples, average MPN 0.6 log10 cfu/g) of cross contamination of non-inoculated green leaf lettuce leaves by inoculated red leaves was observed when the mixed lettuce leaves were cut prior to washing in chlorinated water. In contrast, cross contamination of non-inoculated green leaves was significantly reduced (3.3 percent of sub-samples, average MPN <-1 log10 cfu/g) when the mixed leaves were washed in chlorinated water prior to cutting. This result suggests that whole-leaf sanitizing washes could be a practical means of enhancing the efficacy of chlorine washes for pathogen reduction and cross-contamination prevention.

Last Modified: 8/29/2014
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