Study shows how microbes boost protein content in fermented foods

Researchers studying proteins found in fermented foods like yogurt, cheese, and bread have discovered that a large number and high percentage of proteins created by these microbes contribute to their overall protein content. 

Bacteria have long been used in traditional fermentation and are commonly linked to the health benefits of gut-healthy foods. However, these new findings more specifically pinpoint their nutritional and functional benefits.

“We chose foods that are commonly consumed and are easily accessible at the grocery store,” explains co-author Manuel Kleiner, an associate professor of plant and microbial biology at North Carolina State University (NC State), US.

“What we found surprising is that a large proportion of protein being eaten as part of these foods is actually microbially derived. I found it quite mind-boggling how much of the wheat protein in a regular wheat bread is converted into yeast protein, for example.”

He adds: “When we eat bread, we actually eat quite a lot of yeast.”

Fermented vs. non-fermented

Microorganisms are important to fermented food production as they convert raw substrates into digestible, nutritious, and health-promoting products.

The authors of the paper published in Food and Function were initially curious about how microbial fermentation changes the protein composition of foods. They set out to discover which microbial proteins are commonly consumed in fermented dishes.

Their study looked at 17 fermented and three non-fermented foods. They combined high-resolution liquid chromatography and mass spectrometry to identify all the food- and microbial-derived proteins.

In five of the fermented foods studied — brie cheese, kefir, yogurt, sour cream, and buttermilk — the proportion and diversity of microbial proteins were much higher than food substrate proteins.

Dairy milk, tofu, and wheat bread were the non-fermented foods investigated in the study. Fermented foods were the derivatives of these substrates, such as yogurt, brie cheese, sour cream, plain yeast bread, sourdough bread, tempeh, miso, and soy sauce.

Among all the fermented foods analyzed, brie cheese and kefir had the highest number of microbial species, while plain yeast bread and soy sauce had the lowest.

Proportion and diversity of microbial proteins

In fermented foods, microbial proteins contributed up to 11% of the total protein content by volume and up to 60% of the total number of identified proteins. The researchers note that some of these microbial proteins, such as proteases, could impact gut physiology.

In five of these fermented foods — brie cheese, kefir, yogurt, sour cream, and buttermilk — the proportion and diversity of microbial proteins were much higher than food substrate proteins.

For instance, among the 1,573 different proteins identified in brie cheese, 1,023 proteins (65%) were microbial proteins. The researchers observed this pattern across almost all dairy products in the study.

“This shows that microorganisms not only contribute to the fermentation process itself but also to the overall nutritional and functional profile of fermented food by converting substrate proteins into microbial proteins,” comments Ayesha Awan, a Ph.D. candidate at NC State and co-corresponding author of the paper.

“These results offer future areas for investigation beyond the known probiotic effects of fermented foods, as the microbial proteins consumed as part of these foods may influence the host immune response or interact with the gut microbiota.”

The authors of the study believe their findings could lead to engineering fermented foods with more specific microbial profiles to enhance their health benefits. Awan adds that future research may include studying the health impacts of fermented food proteins on gut microbiomes in mice.

In other fermented food science, researchers examining nine Ethiopian fermented foods and beverages previously proposed that foreign microbial communities may be cultivated to develop next-generation probiotics. Darwin Bioprospecting Excellence identified strains in foods rich in lactic acid species and environmental microorganisms, with dominant and undetected bacterial strains.