Jan. 1, 2011 - Feb. 29, 2012Award Number
Elliot Ryser, Ph.D.
Michigan State University
In response to continued outbreaks involving E. coli O157:H7 and other bacterial pathogens, the safety of fresh produce has now become a top priority. Although bagged salad mixes and other such products available in supermarkets have been commercially washed multiple times in various chemical sanitizers to minimize the risks from hazardous microorganisms, such practices will not totally ensure end-product safety. As product residues accumulate in the water during processing and reduce the effectiveness of commonly used commercial sanitizers, bacterial contaminants in this water are readily transferred to previously uncontaminated product. The study being proposed here will explore some of the water quality issues related to chlorine effectiveness with the goal being to identify several easily measureable water-related factors (example - the amount of lettuce debris in the water) that can be easily monitored by the industry to increase the effectiveness of chlorinated sanitizers.
Chlorine-based and other types of commercial sanitizers for flume tank systems typically reduce microbial populations on leafy greens only 1 to 2.5 logs, making their use both unpredictable and unreliable. Organic matter has a profound impact on sanitizer efficacy with high levels reducing sanitizer performance. Most large commercial produce processers monitor sanitizer concentration, pH and oxidation/reduction potential of the wash water as part of their HACCP plans. However, these three parameters are less than ideal predictors of organic load and sanitizer efficacy with new monitoring tools for organic load clearly needed for improved pathogen control. This multi-institutional proposal focuses on two water-related areas: 1) the identification of new produce flume water parameters that can better predict sanitizer efficacy (Objectives 1 and 2), and 2) the development of a novel disposable filtration device for rapid concentration of E. coli O157:H7 (and potentially other bacterial contaminants) from both flume and centrifugation water (Objectives 3 and 4). In Objective 1, a newly developed simple bench top system consisting of a 5 L jug will be used to assess the efficacy of three commercial sanitizers (XY-12, Tsunami 100, Tsunami 200) at three different concentrations against E. coli O157:H7 in water containing 0 to 10% lettuce slurry which corresponds to the range of organic loads seen in industry. In the next objective, a unique well-characterized small-scale commercial leafy green processing line at Michigan State University will be used to assess the impact of water quality on sanitizer efficacy against E. coli O157:H7 with the starting levels of E. coli on the inoculated lettuce to be determined from Objective 1. In Objective 3, a newly developed disposable single use filtration capsule will first be optimized for quantitative recovery of E. coli O157:H7 from sanitizer-free water containing up to 10% lettuce slurry using the same bench-top system in Objective 1 with E. coli O157:H7 quantitatively recovered by membrane plating and real-time polymerase chain reaction in conjunction with a standard curve. In the last objective, this now optimized single use filtration capsule will be assessed for recovery of E. coli O157:H7 from sanitizer-containing flume and centrifugation water during simulated commercial processing of E. coli O157:H7-inoculated lettuce at Michigan State University. This project will provide the fresh-cut industry with two deliverables - 1) several quick and easy tests for flume and centrifugation water that are likely to be better predictors of both organic load and sanitizer efficacy than pH and ORP which are most widely in industry, and 2) a disposable filtration capsule that is likely to serve as a highly useful and inexpensive tool for monitoring the levels of E. coli O157:H7 and other bacteria in both flume and centrifugation water with the dewatering centrifuge being the logical target for routine testing in HACCP programs.