Improving produce safety by stabilizing chlorine in washing solutions with high organic loads.

Chlorine is widely used by the fresh and fresh-cut produce industry to reduce microbial populations and prevent the potential spread of human pathogens during produce washing. However, the organic materials released from cut produce quickly react with chlorine and degrade its efficacy for pathogen inactivation. A novel food-grade chemical mixture, F86-128, formulated by industry scientists purportedly stabilizes chlorine in fresh-cut leafy green wash systems with high organic materials and thus prevents reduced chlorine efficacy. Prior to commercial adoption, a highly experienced USDA-ARS project team, consisting of microbiologists, food technologists, and chemists, will conduct in-depth studies and expand the research scope to include herbs, tomatoes, and cantaloupes. Laboratory-based studies will be augmented with semi-commercial pilot-plant trials to test real-world conditions, including realistic pathogen contamination patterns of fresh produce and diverse tests to determine appropriate operational conditions for use of F86-128. We will confer with CPS and industry to ensure that the findings will be not only scientifically rigorous but also commercially applicable. Successful completion of this project will provide objective and thorough scientific evaluation of the effectiveness of F86-128 for improving produce safety by stabilizing chlorine, thus facilitating the industry in making informed decisions on F86-128 development and commercialization.

Chlorine solutions are widely used in the fresh and fresh-cut produce industry to reduce microbial populations and prevent pathogen survival and transference during water re-use and re-circulation. However, the copious amount of organic material released from the cut edges of vegetables, and the presence of field soil and debris creates a high demand for free chlorine, reducing the sanitizing potential of wash water just when it is needed most. Balancing the need for sufficient levels of free chlorine for effective sanitizing with the need to limit formation of hazardous chlorine off-gas during the commercial fresh-cut produce wash operations is a technical challenge. Industry scientists have pioneered development of a novel food-safe (GRAS) chemical product, F86-128, that they found stabilizes chlorine as hypochlorous acid in the presence of high organic loads, thus minimizing the loss of chlorine efficacy in produce wash tanks and flumes. The promising industry research results on F86-128 and hypochlorous acid need to be verified and the effective operational range under various conditions need to be tested by impartial third-party researchers before such products can be introduced to the fresh produce processing industry. This proposal describes several types of studies to be conducted by a USDA-ARS research team to address queries posed by industry, specifically: 1) Evaluate the effect of compound F86-128 on the stability of hypochlorous acid in the presence of high organic load, and determine the influence of organic load, pH, chlorine, and temperature on the effectiveness of F86-128 stabilization of hypochlorous acid; 2) Determine the effect of F86-128 on the pathogen inactivation potential of chlorinated wash water for leafy greens; 3) Determine the effect of F86-128 on the pathogen inactivation potential of chlorinated wash water for other fresh produce including herbs, tomatoes, and cantaloupes; 4) Evaluate the effect of F86-128 on product quality and shelf life, and measure residual levels on finished products. Key features of this proposal include inoculation protocols that simulate realistic field contamination with E. coli O157:H7, Salmonella, and Listeria, use of a pilot-scale fresh-cut facility to simulate commercial wash processes and efficacy evaluated on herbs, tomatoes, and cantaloupes and with biofilms, as well as close consideration of industry concerns and operational limitations. These features will aid development of procedures that are amenable to industrial use, and support rapid, economical adoption of effective sanitization improvements by commercial processors.

1. Evaluate the effect of T-128 on the stability of hypochlorous acid in the presence of high organic matter load; determine the influence of common produce wash operation conditions on the effectiveness of T-128. 

2. Determine the efficacy of T-128 in enhancing pathogen reduction, reducing pathogen survival and transference in chlorinated wash water processing of leafy greens. 

3. Determine the efficacy of T-128 in enhancing pathogen reduction, reducing pathogen survival and transference in chlorinated wash water processing of herbs, tomatoes, and cantaloupes. 

4. Evaluate the impact of T-128 on produce quality and shelf life, and analyze the residue levels on finished products.

In summary, our research provides an objective evaluation of the effect of T-128 on chlorine stabilization, pathogen reduction, cross-contamination prevention, and pathogen biofilm sanitization in high organic load washing conditions. The extensive laboratory and pilot-scale tests addressed the major questions posed in the initial CPS-RFP for the project: a) How does the adjuvant T-128 in combined use with hypochlorous acid compare to other common (hypochlorous acid, etc) wash water sanitizers in the presence of high organic loads? - Enhanced maintenance of the active antimicrobial in solution o Ability to maintain microbial control of the wash solution - Prevention of leaf to leaf cross-contamination b) At what level of organic material, pH or temperature does the enhanced stabilization of hypochlorous acid by T-128 breakdown? c) Is T-128 effective in wash systems designed for vegetables and fruits other than leafygreens? Our results show that: 

• T-128 is beneficial in maintaining a more stable chlorine concentration under the conditions of typical high organic loads in process wash water (RFP focus a and b above; Objective 1)

• T-128 significantly reduced the potential for pathogen survival in solution and crosscontamination when free chlorine in the process wash water was near depletion (RFP focus a and b; Objective 2) 

• T-128 significantly reduced survival of pathogens on tomatoes and infiltration through the stem scars; and also reduces pathogen populations in biofilms formed on either cantaloupe rind or stainless steel surfaces in a concentration, pH, and exposure time dependent manner (RFP focus c; Objective 3) 

• T-128 at the recommended application rate showed no detrimental effect on fresh-cut lettuce quality (Objective 4). We did not test for T-128 residuals on the produce or in the wash water because the industry partner provided us a letter from the FDA indicating that they had no objection to the use of the T-128 formulation for washing fresh-cut produce. These results suggest that T-128 can be used to improve the safety of fresh produce at the washing stage of processing without compromising product quality.