P3-48 Indicator Methods to Evaluate Process Controls for Fresh Produce

Wednesday, July 25, 2012
Exhibit Hall (Rhode Island Convention Center)
Annemarie Buchholz, U.S. Food and Drug Administration, Bedford Park, IL
Emily Jackson, U.S. Food and Drug Administration, Bedford Park, IL
Ravinder Reddy, U.S. Food and Drug Administration, Bedford Park, IL
Mary Lou Tortorello, U.S. Food and Drug Administration, Bedford Park, IL
Introduction: The microbiological quality of leafy green processing water is currently evaluated through the use of bacterial indicators. Microbial monitoring of pre- or post-harvest waters may be a useful component of risk reduction strategies.

Purpose: The goals of this study were to compare traditional and automated quantification methods for microbial indicators, to reduce the labor and materials required for analysis, and improve process control. 

Methods: Triplicate water samples (0.5 l) of end-of-day flume water (FW) with and without increased organic content and water drained from the centrifugal drier (CDW) were inoculated to contain approximately 5, 10 or 100 CFU/ml Escherichia coli 8739. Total organic carbon was measured for each sample. Samples and negative controls were analyzed by traditional plating methods and with the bioMerieux TEMPO automated MPN, in duplicate. MI agar was used for quantification of generic E. coli and total coliforms, violet red bile glucose agar was used for enumeration of Enterobacteriaceae, and total viable counts were determined by plating on trypticase soy agar. The plating results were compared to the results from the corresponding TEMPO assays.

Results: Uninoculated FW and CDW contained an average of 1.75 and 0.89 log CFU/ml total coliforms and 0.35 and 0.94 log CFU/ml Enterobacteriaceae, respectively. The average total viable counts for FW and CDW were 3.84 and 2.60 log CFU/ml, respectively. No E. coli was detected in either water type. Traditional and automated methods of microbial quantification were comparable (P > 0.05) with the exception of coliforms in inoculated CDW samples. The FW inoculated at 5 CFU/ml and 10 CFU/ml with increased organic content also showed significant differences between the coliform enumeration methods (P < 0.05).

Significance: Based on these findings, the TEMPO system may be an appropriate means for microbiological monitoring of produce process waters. This system could be used to rapidly assess the effectiveness of process controls or indicate a process failure.