Simulation model of quantitative microbial risk assessment model during processing of fresh cut lettuce

Abstract

Scope and Method of Study:

The objectives of this study were to build a quantitative risk assessment model, develop a computer simulation program, and model the occurrence, death and/or survival of groups of microorganisms in lettuce from trimming all the way through de-watering and packaging. Baseline microbial data was used and 10,000 iterations were simulated using Monte Carlo simulation by @RISK soft ware. Risk estimates and sensitivity analysis were used to determine the relevance of each processing unit during fresh cut processing.

Findings and Conclusions:

The simulated model predicted that the process of shredding is the biggest contributor to the total aerobic and coliform bacteria estimates in fresh cut lettuce production. Washing with chlorinated water was not predicted to greatly reduce the microbial load for all three groups of microorganisms. In fact, sensitivity analysis predicted that washing actually contributed to an increase in yeast, mold, and coliform counts in the lettuce. The process of centrifugation was predicted to contribute the least to both the aerobic and coliform bacteria estimates. On the other hand, it was predicted to contribute the most to yeast and mold counts in lettuce processing.