Enhancing the efficacy of fresh produce washing operations through establishing monitoring methods and water disinfection technologies based on a combination of filtration and UV.

The washing of fresh produce is an important step in commercial processing to remove field-acquired contamination. In the course of commercial fresh produce processing the microbial loading and organic loading of the water increases. Consequently, the microbial loading in the water decreases the efficacy of the wash process and increases the potential for contamination to spread through to subsequent product batches. It is common practice to partially or fully replenish tanks with fresh wash water although the timing is largely subjective as opposed to being based on a quality indicator. In the proposed project, a measurable wash water parameter(s) that can be monitored in real time will be identified to report on the microbiological quality. This will enable processors to more accurately identify when the water requires to be changed in order to maintain the efficacy of the wash process and reduce cross contamination events. In addition, a cost effective water-recycling unit will be developed based on a combination of filtration and ultraviolet light. By recycling the efficacy of the wash water process will be maintained with cost savings in resources through reduced consumption and waste-water treatment.

Washing of fresh produce is considered a Critical Control Point despite only limited log count reductions being achieved regardless of the sanitizer applied. However, of more concern is the accumulation of microbial contamination within wash water tanks that ultimately decrease the log count reductions achieved and also leads to extensive cross-contamination events thereby compromising food safety. To maintain wash water quality, tanks can be partially or fully replenished thereby minimizing the accumulation of microbial loading. However, the timing of when to change water in tanks is subjective thereby leading to “good water” being discarded or using the same water for too long. The following proposal will identify wash water parameter(s) (including but not limited to conductivity, turbidity, oxidation-reduction potential or temperature) that can be used to measure the microbiological quality of water in real time. By correlating microbial loading and log count reductions obtained with wash water parameters it will be possible to set critical limits to identify when the wash water should be replenished or replaced. Data will be collected from commercial leafy green processors with sampling trials been undertaken over an entire processing period. A further objective of the study will be to develop a low cost water recycling system based on using filtration in combination with UV Taylor Couette reactor (CT-reactor). The CT-reactor enhances the decontamination efficacy of UV by ensuring efficient mixing in compact unit compatible with high flow-rates. It is estimated that recycling water will save a small-medium sized operation over $200, 000 per year.

1. Determine the efficacy of fresh produce washing within commercial processing facilities. Correlate the log count reduction achieved with wash water parameters (temperature, turbidity, conductivity, Oxidation Reduction Potential, oxygen consumption, impedance/capacitance). 

2. Determine the cross-contamination events occurring during commercial wash processes. 

3. Evaluate the efficacy of a combination of filtration and UV to recycle fresh produce wash water. 

4. Perform verification trials on selected interventions and monitoring methods

The overall objective of the research was to establish which parameters associated with the wash water process could be used as a metric to predict the log count reduction achieved, in addition to identifying cross-contamination events during the wash process and finally develop methods to ensure consistent washing of leafy greens by water recycling. The results from the study illustrated that the log reduction from the wash process was dependent on the initial loading on the leafy greens, low temperature and conductivity (charged solutes content). Although the LCR was independent on the microbial loading of the water it was noted that carriage of coliforms on the post-washed produce was dependent on the levels encountered within the wash tank. The results are consistent with the finding of the microbial population studies that illustrated that not all microbes are deposited in the wash water and disseminated to other batches via crosscontamination events. Although coliforms appear to be more readily disseminated via wash water it is unclear if the findings can be extrapolated to the behavior of pathogens such as E. coli O157:H7 or Salmonella. It was noted that lettuce appeared to accumulate a greater degree of microflora from wash water compared to spinach despite the latter having a rough surface topography. There was tentative evidence that the different members of the leafy greens microbiota differed with respect to remaining on the leafy greens or being deposited in the water. Although not studied to any great extent, it was interesting to note the microflora residing on lettuce could utilize plant related sugar alcohols those in the wash water metabolized organic acids. A water recycling system was developed based on an initial coagulation step followed by filtration and a final UV disinfection step. Through optimization trials the coagulant of choice was sodium aluminate and could rapidly coagulate the colloidal organics within spent wash water when combined with vigorous mixing. Commercial trials verified the performance of the water recycling unit to decrease the organic loading in the wash water and microbial counts.