Thermal Processing and Safety of RTE Foods

Man slicing deli meat

Thermal processing has long been the industry standard for making sure ready-to-eat (RTE) foods are also safe to eat. Thermal treatment is particularly effective for pasteurizing meat and poultry products to rid them of harmful bacteria, like Listeria.

This article outlines what thermal processing is and its main safety benefits for RTE foods.

What is thermal processing?

Put simply, thermal processing is applying heat to food. Most processing applications expand on that definition by applying temperature and time requirements (i.e., heating foods to a particular temperature and maintaining that temperature for a particular duration).

Any given food product may go through multiple stages of thermal processing prior to its consumption. An onion, for example, may be flame pasteurized and peeled before being chopped and cooked into a soup, which is then put through a post-package pasteurization process. Then, the soup goes through one more thermal processing step (usually in the microwave or on the stovetop) when the consumer gets it home.

Many RTE products, particularly meat and poultry, go through at least two phases of thermal processing: cooking and pasteurization/sterilization. Both of these processes seek to reduce any bacteria that may be present to a level that’s safe to eat. In regulatory terms, this is referred to as “lethality.”

Cooking

The goal of this step, other than cooking the product so it tastes good, is to ensure that it’s rid of pathogens like Salmonella. To help processors accomplish this goal, the USDA’s FSIS created Appendix A: Compliance Guidelines for Meeting Lethality Performance Standards for Certain Meat and Poultry Products.

This document, published in 1999 and still used extensively throughout the food industry, establishes minimum internal temperature and duration guidelines for reducing Salmonella. While the guidelines were validated only for cooked beef, roast beef, and cooked corned beef, they are commonly applied to other products as well.

For more specific information about what it takes to kill different microorganisms in different products, the American Meat Institute developed a Process Lethality Determination Spreadsheet. Processors can enter real process data into the spreadsheet, and it will automatically calculate the temperatures and times required to destroy the target organism.

Pasteurization/Sterilization

After being cooked to get rid of Salmonella and other pathogens typically found in raw food, RTE foods (especially meat and poultry) must go through a further processing step to ensure they don’t contain any additional contaminants, like Listeria.

This is where pasteurization and sterilization come in.

Pasteurization and sterilization aren’t the same thing. Pasteurization primarily removes pathogens (i.e., harmful microorganisms), while sterilization removes all microorganisms whatsoever.

Sterilization doesn’t require heat. It can be accomplished thermally, but also through the use of chemicals and other methods.

Pasteurization requires either heat or pressure. It can be done either pre- or post-packaging. Pre-package surface pasteurization is particularly effective for RTE deli products, like roasted turkey. Post-package pasteurization is more commonly used for ready meals.

Learn more about the different types of thermal pasteurization and their applications.

Advantages of thermal processing for RTE foods

Most of us can attest to the benefits of cooking our food. But sometimes scientific verification is nice, too.

The authors of a 2010 review article in the journal Molecular Nutrition and Food Research, summed up the benefits of thermal processing:

  • Inactivation of food-borne pathogens, natural toxins, or other detrimental constituents
  • Prolongation of shelf-life
  • Improved digestibility and bioavailability of nutrients
  • Improved palatability, taste, texture, and flavor
  • Enhanced functional properties, including augmented antioxidants and other defense reactivity or increased antimicrobial effectiveness

That’s just a lot of science-speak for “thermal processing makes food safer and tastier.”

For the post-processing step, however, thermal isn’t the only game in town. In recent years, high pressure processing (HPP) has gained immense popularity.

Both types of processing — thermal and high-pressure — are effective for increasing food safety. And they both have advantages for different applications. Here are two advantages of using heat:

  • Thermal processing has a wider range of applications. HPP can kill microorganisms, but not their spores. Because of this, some products, like certain dairy and low-acid foods, can’t be processed using pressure. This FDA article has a good roundup of what foods are — and aren’t — safe to process using HPP.
  • High pressure processing is much more expensive. A cost analysis in a 2014 issue of Food and Bioprocess Technology calculated that HPP is seven times more expensive than thermal processing. HPP suppliers are actively working to reduce this cost. But for the time being, the capital expenditure is prohibitive for many food processors.

And there’s your intro to thermal processing and safety for RTE foods! In the next article, we’ll take a look at the relationship between thermal processing and food quality.

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