Multifactorial Food Preservation

An image of a petri dish containing colonies of bacteria gram negative bacilli/ Gram negative cocco bacilli .

Multifactorial Food Preservation

CONSUMERS WANT LESS SEVERELY (in other words, minimally) processed foods. They also desire their foods to be formulated with clean label ingredients when possible, and they prefer packaging that is recyclable and sustainable. Jairus David, Ph.D., Principal Consultant, JRD Food Technology Consulting, LLC, provided a detailed overview of minimally processed foods and how hurdle technology can be used to ensure the safety and quality of these products—while still meeting consumers’ demands. His presentation, “Hurdle Technology: Multifactorial Food Preservation for High Quality Foods,” was prepared for the 2020 Clean Label Conference.

The spectrum of food processing categories ranges from “Not Preserved, Raw” (fresh foods) to “Heat Preserved” (fully modified). Minimally processed foods fall just after “Not Preserved, Raw” in this continuum and are similar to fresh foods, in terms of product quality. USDA defines minimally processed products as those “processed in a manner that does not fundamentally alter the product,” while FDA does not define the term.

Four major design principles can be used when developing a minimally processed food. First, thermal or nonthermal processing may be applied to inactivate microorganisms. Thermal treatments may include pasteurization at 70˚C for two minutes to control Listeria monocytogenes (“L. mono cook”) or at 90˚C for 10 minutes to control non-proteolytic Clostridium botulinum (“non-prot bot cook”). Secondly, the food matrix may be formulated to maintain preservation by modifying the pH or water activity, or by the addition of an antimicrobial. Next, packaging (which may contain a modified atmosphere to inhibit microbial growth) is used to prevent product contamination. Finally, the product will need to be kept continuously refrigerated, including during distribution and storage, to maintain safety and quality.

David reviewed the food poisoning microbes of concern in minimally processed refrigerated foods. Listeria monocytogenes, Yersinia enterocolitica and Aeromonos hydrophila can grow at refrigeration temperatures but are easily heat inactivated by an “L. mono cook” step. Salmonella spp., Vibrio parahaemolyticus, pathogenic E. coli strains and Staphylococcus aureus are also inactivated easily, and they cannot grow at refrigeration temperatures.

In contrast, non-proteolytic Clostridium botulinum and certain Bacillus spp. may grow at refrigeration temperatures and are heat-inactivated by “non-prot bot cook.” Finally, proteolytic C. botulinum and C. perfringens have higher heat resistance—but cannot grow below temperatures of ~10°C—which makes them of particular concern in temperature-abused products, due to their ability to produce toxins.

Chart showing food processing categories from "Raw" to "Heat Preserved" indicating various stages of food preservation and shelflife quality.

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Combinations of different tools or “hurdles” are typically employed to control microbial growth in minimally processed foods. Many metaphors have been developed to illustrate the hurdle approach used in foods. David discussed the traditional “boiled egg” model, which describes each antimicrobial factor as a separate “boiled egg” obstacle of differing heights and widths, according to its individual strengths in controlling the pathogen. A weakness of this model is that it cannot account for synergies or interactions between the “eggs.”

In the hurdle race metaphor, the hurdles are of the same height and are equidistant from each other, suggesting that each antimicrobial or process must be used at full strength. However, each hurdle should be used at suboptimal levels for minimally processed foods—otherwise, they won’t be “minimally processed.” Redundant antimicrobials or processes will negatively impact product quality.

As an alternative, David Legan and Jairus David have proposed a “pole vault” model. The individual hurdles stack together on top of each other to create a high barrier for microbial growth. [Note: To see graphic representation of these models, search for this presentation online at]

Using another analogy, David compared the use of multiple antimicrobial processes to a radio. An old-school radio may have only a few dials, so fine-tuning is not possible. Processed foods which utilize only a few hurdles may end up being severely processed. In contrast, a modern synthesizer may have dozens of controls, each of which can be finely adjusted to provide exquisite sound quality. Multiple factors are used in minimally processed foods that are in the marketplace, with more than 10 “dials” used for some products. Adding multiple hurdles to a product will increase a product’s cost, but it also increases a product’s value and ensures product quality and safety.

“Hurdle Technology: Multifactorial Food Preservation for High Quality Foods,” Jairus R. David, Ph.D., Principal Consultant, JRD Food Technology Consulting, LLC

This presentation was given at the 2020 Clean Label Conference. To download presentations from this event, go to

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