Using a Blanching Process to Control Pathogens on Produce

Every summer, I sit under the carport with my family and shuck a few buckets of corn that we later boil and quickly freeze. I never thought much about that home process until I started working at the Mérieux NutriSciences Food Science Center and regularly interacting with customers on a much larger and elaborate scale doing the same thing with their vegetables.

Blanching vegetables improves product quality by changing the texture and preserving the flavor and color, but it can also serve as a critical control point regarding pathogen inactivation. 

The U.S. Food and Drug Administration’s (FDA) Food Safety Modernization Act (FSMA) requires facilities to implement a food safety system incorporating validated process controls to eliminate food safety hazards.

Thermal treatments like water blanching and steam blanching can be used to reduce or eliminate foodborne pathogens like Salmonella, Escherichia coli O157: H7, and Listeria monocytogenes that can be found in raw vegetables. Typical water blanching temperatures range from 70⁰C to 100⁰C. Steam blanching, typically used for finely cut and smaller vegetables, will employ steam for several minutes.

When validating the process, there can be a couple of different approaches. The first would be to use an appropriate surrogate culture, as most equipment is located in a facility that cannot process samples that are inoculated with pathogens. Products are inoculated at a high level and then treated. The inoculated, untreated controls, and inoculated treated samples are collected and enumerated in the laboratory.

The difference between the untreated and treated sample demonstrates the log reduction. Meshes or metal bags can be sent through the system depending on the process. A whole batch may need to be inoculated, or samples could be color coded. For example, bell peppers using red and green peppers can be used simultaneously to differentiate which ones are inoculated or not.

The second approach would be an in-lab study using the pathogens of concern. This works well for processes that can be easily mimicked in the lab following time and temperature parameters as the production facility prescribes. A water or steam bath is used, and samples are again inoculated at a high level, treated, and enumerated to observe what log reduction is achieved.

An expert scientist can review those parameters for locations with many different types of produce and processing parameters, making evaluation recommendations. Common parameters to review include product description, process description, cut size, time, temperature, and bed depth.    

Although blanching is a common practice, even amongst consumers, it’s good to know whether that process is effective enough against pathogens of concern. Contact us to share about your products and process so that a validation study can be custom designed for your needs.