Summary of Awards to Date

Establishment of critical operating standards for chlorine dioxide in disinfection of dump tank and flume water for fresh tomatoes.


Oct. 1, 2009 - Sep. 30, 2010

Award Number


Funding Agency

Center for Produce Safety

Amount Awarded



Trevor Suslow, Ph.D.
University of California, Davis


M. Danyluk


Layman Abstract:

The establishment of sanitary standards and defined disinfection treatment doses is essential for the responsible handling and packing of fresh tomatoes. Adequate water treatment to minimize bacterial cross-contamination is a fundamental management prerequisite to providing customers with tomatoes that are safe to consume. Liquid chlorine, similar to household bleach, in forms approved for use on fresh produce has been the dominant water treatment. More recently, renewed interests in alternative sanitizers, such as chlorine dioxide, with simpler dosing requirements and lesser concerns for harmful by-products and residues has developed from within the tomato industry. There is inadequate science-based performance data to base sanitary standards and reliable audit inspection criteria for chlorine dioxide use in dump tank and flume water. The purpose of this research project is to develop a baseline of data assessing the reliability of chlorine dioxide injection into tomato packing house water systems. A total of twelve full-day surveys will be conducted under Florida and California seasons within commercial facility management operations and conditions. The research outcomes will allow the assignment of a research-based starting point for evolving national and international tomato-specific standards for water quality dosing, monitoring, process controls, and corrective actions with chlorine dioxide.

Technical Abstract:

From an industry and public heath regulatory perspective, postharvest water quality management represents one of the few unit operations that approach a true critical control point for fresh produce. For fresh tomatoes, much attention has been focused on the importance of dump and flume tank water sanitation for several years due to the recognized potential for introduction and widespread cross-contamination of human pathogens from incoming fruit and environmental sources that may occur. However, while rich in model systems data, little publically accessible data from commercial practices to adequately predict or set functional performance standards in commercial pack and re-pack operations is available to standardize effective control point parameters. The lack of verified and accepted compliance criteria remains a significant barrier and concern for the establishment of audit standards and limits for the fresh tomato industry. Renewed interest and promising recent model system work with chlorine dioxide (ClO2) exist for fresh tomatoes, however very little is known about the management of this sanitizer in dump tank and flume water. On-site surveys conducted in packing facilities located in California and Florida, with matched ClO2 generation systems, will measure bacterial loads of incoming fruit, fruit pulp temperature, water temperature, pH, ClO2 levels, turbidity, conductivity, total suspended solids, redox potential (ORP), and bacterial loads of treated water over a full packing shift on twelve selected seasonal dates. Laboratory studies, using simulated dump water, will further determine and refine dose efficacy for log-reduction of Salmonella in this water and the relationship between ClO2 dose (ppm), ORP (mV), and turbidity (FAU/NTU) as influenced by water temperature. In summary, this proposal will develop scientifically-based critical operating standards for chlorine dioxide use in dump tank and flume tank waters directly applicable for the fresh tomato industry.