January 28, 2021

Hutkins, international panel find consensus on definition, properties of fermented foods

Pocket Science: Exploring the 'What,' 'So what' and 'Now what' of Husker research



Welcome to Pocket Science: a glimpse at recent research from Husker scientists and engineers. For those who want to quickly learn the “What,” “So what” and “Now what” of Husker research.



The process that turns milk into cheese, cabbage into kimchi and grape juice into wine might have seemed miraculous to the humans who first encountered the phenomenon thousands of years ago. If its origins were once mysterious, though, some of its benefits would have been readily apparent: longer preservation via less spoilage, more palatable taste or texture, intoxicating after-effects.

It’s a process now known as fermentation, which accounts for an estimated 5,000-plus varieties of food and drink from every region on the planet. But for all of its popularity, and for all that scientists now understand of what occurs during it, questions have remained about how to define fermented foods. Questions also persist around the nutritional benefits of fermented foods and the role of fermentation microbes in human health.

So what?

To address these issues, the International Scientific Association for Probiotics and Prebiotics convened an expert panel of 13 scientists. Led by Nebraska’s Robert Hutkins and the University of California, Davis’s Maria Marco, the panel consisted of microbiologists, food scientists, nutritionists, and health care professionals from North America, Europe and Asia.

Hutkins and the panel first arrived at a consensus definition of fermented foods: “foods made through desired microbial growth and enzymatic conversions of food components.”

The simple definition clarifies several points:

  • The word “desired” makes clear that whatever changes occur during fermentation, the outcome is intentional and preferred. This distinguishes fermentation from the other possible and undesirable outcomes of microbial growth, namely spoilage.

  • To qualify as fermented, the end products must result from the activities of bacteria or fungi that catalyze enzymatic conversions — sugars into carbon dioxide and alcohol, for instance.

  • Foods transformed only by chemical processes, rather than microbial-driven activities, do not qualify. For example, vegetables preserved via pickling processes do not involve microorganisms and would not be considered as fermented.

The panel noted that although microbes are required to produce fermented foods, those microbes are not always present in the final product. For example, breads are baked and beer is pasteurized or filtered, leaving those products devoid of live microbes. By contrast, yogurt, kefir and kombucha may contain billions of live microbes. Many of those microbes survive digestion and reach the gut.

Now what?

The panel also provided guidance to public health professionals, consumers and other scientists about the role of fermentation microbes and their metabolic products on the gut microbiome and human health. In particular, they explained differences between fermented foods and probiotics, along with the challenges of designing clinical studies to evaluate health outcomes.

Finally, the panel noted that advances in molecular biology, ecology and bioinformatics may ultimately lead to new and improved fermented foods that taste better, last longer and provide health-promoting benefits.