In this interview conducted at Pittcon 2024 in San Diego, Maria Marco discusses her research on the health benefits, safety, and waste reduction potential of fermented foods, and the microbial processes involved in their production.
Please could you briefly introduce yourself and your current research focus?
I am Maria Marco, a professor in the Department of Food Science and Technology at the University of California, Davis. I am a microbiologist passionate about microbes that are good for our health, particularly those found in foods and our digestive tracts. I am particularly interested in microbes that we call lactic acid bacteria. This fascinating group of microbes is essential for making fermented foods and is often called probiotics. I am interested in what they do and why they are good for us.
What is meant by fermented foods, and why have they been hitting the headlines so much in recent years?
Fermented foods are foods and beverages made by microbes and include many different kinds of foods like bread, sauerkraut, yogurt, chocolate, wine, beer, kombucha, and coffee. Many beverages are fermented, including wine, beer, kombucha, and kefir.1
There are two main reasons for fermented foods. Fermented foods are in the headlines at the moment because chefs at top restaurants worldwide have started exploring them because of their diverse flavors and sensory properties.
Another reason fermented foods have become more popular is that dieticians have started to consider them because of the health benefits they can bring.
In the US, dieticians have ranked fermented foods as the number one superfood for six years running—above salmon and berries.2 I do not think we have all the answers to whether this is entirely true, but the belief is certainly out there that fermented foods are good for us.
Do you think that belief has helped catalyze research interest? Do you think it has been beneficial to your research community?
Definitely. So much of our research is driven by public interest—what is important and valuable.
Fermented foods have been made for thousands of years, so they are not new. With the available tools, what we can do in the lab is much greater than what we could do a decade or two ago.
It is a unique moment for bringing together the basic understanding of fermented foods to the bigger picture of how they can help our health.
What impact can the study of fermented foods have on matters of safety, diet, and even food waste?
Fermented foods are generally safer than the ingredients used to make them. For most of the world, where access to clean water is unfortunately still a problem, drinking beer could be safer than drinking the water. That has been true for much of human history. Fermented things are generally safe because of the chemical environment. That acidic flavor creates an environment that pathogenic microbes do not like.
Image Credit: ivector/Shutterstock.com
Now, let us talk about waste. We can take spoiled or defective foods and upcycle them through fermentation. We can take those lactic acid bacteria I mentioned and ask them to ferment imperfect fruits and vegetables and make them into a new, desirable product. When we ferment, we are preserving food.
Diet is the crux of the matter. Think about the excitement over fermented foods today. If we have cabbage or a cucumber, we know that that is generally healthy. When we add a little salt and let those microbes grow, they digest the food for us and make it easier to digest. Those microbes give new bioactive compounds to these foods, changing milk, berries, cabbage, etc., into something more nutritious than what we started with.
In your talk, you mention the unique challenges in producing fermented foods. Could you elaborate on these challenges, especially in relation to microbial growth and metabolism?
Fermented foods are living foods and anything alive is unpredictable.
I think that is why chemistry was the answer through most of the industrialization of our food supply. By that, I mean adding compounds.
In the past 10 years, we have turned a page, and now many of us ask, "What is the biology of the foods we eat?" With that comes a lot of opportunity, and the issue is that microbes can be unpredictable. Just as we need microbes to make fermented foods, some of those same microbes or sometimes unwanted contaminants spoil the foods or have quality defects in how they look or taste.
When we make fermented foods, we constantly manage our microbial gardens—we do not want weeds in there. I think that is a particular challenge with fermented foods.
Just as we have a garden with a row of carrots, each one may grow slightly differently and have a slightly different look and flavor. Just one species of microbes has all that. However, you normally combine different fruits and vegetables if you want a nice salad. I think that is how we can think of fermented foods.
How do industrial starter cultures in cheese production impact manufacturer reliability and consistency?
Industrial starter cultures are microbes grown specifically in a pure or well-defined culture. They have transformed fermented food manufacturing from a small scale to a large industrial scale. We would not have beer, wine, or cheese on the scale we have today if it were not for starter cultures.
Pittcon Thought Leader: Maria Marco
They work most of the time, but sometimes they do not work as planned. Even in the best scenario, microbes will be microbes, and it is not entirely predictable. You cannot control them all the time. Starter cultures are really important. They have been valuable for the industry but are not infallible.
Currently, we do not have reliable starter cultures for making our fermented fruits and vegetables. Although we have starter cultures for making yogurt and cheese, we could grow in this area and make fermented fruits and vegetables more accessible by having starter cultures available. This would make those foods more reliably made with fewer defects.
What techniques are currently used to measure and monitor the quality of fermented foods and how have these methods evolved?
As with much microbiology, from medical to environmental, we still rely on 19th-century methods. The bacteria are cultured on a Petri dish, with a lab coat and goggles.
This is still the most common method, but it is problematic. As I said, it was developed in the 1800s. We have turned to more culture-independent methods, where we do not grow those bacteria on a Petri dish. Instead, we look at their nucleic acids and genetic material to inform us about who they are and what they are doing.
That technique has a lot of power because we can examine whole communities of thousands of different microbes and hundreds of different species at once.
In your presentation, you mention using culture-independent microbial analyses and DNA sequencing. How have these techniques transformed how we identify and diagnose product defects in fermented foods?
We have been pretty successful in using these methods. We were able to identify a ‘smoking gun’ of spoilage. We used DNA sequencing analysis to look at the microbial composition of fermented olives and cheese to identify the most likely culprits of spoilage.
For fermented olives, there was a spoilage event. The olives smelled and even tasted as they should, but they were very mushy. We hypothesized that some microbe could eat pectin.3 We identified the microbes in the olives and found, through culture-based methods, that pectinolytic yeast is a problem with these olives.
That was the first step we took in looking at spoilage issues with fermented foods, and since then, we have applied similar principles to, for example, understand how cheddar cheese gets cracks.4
Cracks may be nice to look at in cheddar cheese, but when making a lot of cheese and the purpose is to slice or grate it in large-scale production, cracks are not allowed; otherwise, you will have to throw away a lot of cheese. We helped a company identify which microbes cause this defect, as they would call it.
How can exploring strain-specific diversity contribute to developing new fermentation processes, particularly for fruit and vegetables?
Just as we are people with different interests and hobbies, if I take two isolates of our favorite bacterial species, Lactiplantibacillus plantarum, from the same food, they can have completely different properties. One may do a great job fermenting the food while the other does not, yet they coexist.
We are getting into the fine-scale here and finding a deep resolution of understanding when we get down to strain-specific differences.5 Although they are the same species and will still make lactic acid, we may have very different outcomes in a fermentation process depending on which L. plantarum strain we add.
We are interested in understanding how these two very different family members can live together and what happens when we separate them.
We are reaching the edges of what we can do with DNA sequencing-type methods. We can look at the genomes when we look at those strain-level differences. We know they are different genetically, but we still have a lot of questions about what that means and how to distinguish them from each other when we use DNA-based approaches in the fermentation community.
Based on your experiences at Pittcon and research, what future directions do you see for fermented food and drink research?
I like the idea of guided fermented food production, where we aim for specific health benefits. However, we do not have much evidence from human studies to rely on. We feel that fermented foods are good for us, but not many studies have verified this collectively or individually.
We need to keep pushing to continue the study of these foods and ultimately make them accessible. We should not be paying ten dollars for a little shot of sauerkraut. It should be something we can make at home.
There are so many headlines focusing on the health aspects and not so many on the food waste side. Why do you think there is so much focus on health, even though some concrete studies show benefits regarding food waste and sustainability?
I think it comes down to economics. When it becomes too expensive to put food into a landfill, perhaps we will start regulating against that when there is an economic need or a push to protect our food supplies.
If we can control those fermentations a bit more, reusing food this way will become more commonplace. You will have to rebrand the food, but people will want to eat it as long as it tastes good. It will not last very long on supermarket shelves if it does not taste good.
The complexities of the food processing and distribution lines present challenges. How do we get the food from the supermarket or the farmer and then use it? There are some logistical challenges to work out; maybe that is why we do not hear about this option as frequently as we do about the health benefits of these foods.
As we mark the 75th anniversary of Pittcon, could you share your first memory or experience of attending this conference and how it has impacted your view on the scientific community?
Pittcon is a vibrant conference. What strikes me about this meeting is the diversity of disciplines represented. It is a big tent for chemists, biologists, physicists, mathematicians, and potentially anybody interested in understanding the basic chemistry of life and the planet.
What are you most looking forward to at Pittcon San Diego this year?
The product show is the best place to go. It is difficult to decide which sessions to attend when so many exciting events happen simultaneously. They are full days.
Where can readers find out more?
- 1Dietitian, P. C. T. (2024) Affordability and Gut Health Predicted as Leading Food Purchase Drivers in 2024, PR Newswire: press release distribution, targeting, monitoring and marketing. Available at: https://www.prnewswire.com/news-releases/affordability-and-gut-health-predicted-as-leading-food-purchase-drivers-in-2024-302061882.html (Accessed: 1 July 2024).
- 2Marco, M.L., Sanders, M.E., Gänzle, M. et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol 18, 196–208 (2021). https://doi.org/10.1038/s41575-020-00390-5
- 3Alimardani-Theuil, P., Altschul, S. F., Arroyo-López, F. N., Gregori, R., … Cole, J. R. (2012). Effects of pectinolytic yeast on the microbial composition and spoilage of olive fermentations. Food Microbiology. https://www.sciencedirect.com/science/article/abs/pii/S0740002012001967?via%3Dihub
- 4Xue, Z., Brooks, J. T., Quart, Z., Stevens, E. T., Kable, M. E., Heidenreich, J., … Marco, M. L. (2021). mSystems, 6(1). doi:10.1128/msystems.01114-20 https://journals.asm.org/doi/10.1128/msystems.01114-20?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub++0pubmed
- 5Yu, A. O., Goldman, E. A., Brooks, J. T., Golomb, B. L., Yim, I. S., Gotcheva, V., … Marco, M. L. (2021). Microbial Biotechnology, 14(5), 1990–2008. doi:10.1111/1751-7915.13871 https://enviromicro-journals.onlinelibrary.wiley.com/doi/10.1111/1751-7915.13871
About Maria Marco
Dr. Maria Marco is currently a Professor in the Department of Food Science and Technology and Chair of the Food Science Graduate Group at the University of California, Davis.
She earned her bachelor’s degree in microbiology at The Pennsylvania State University and her PhD in microbiology at the University of California, Berkeley. As a postdoc at NIZO food research in The Netherlands, she developed a love for lactic acid bacteria and the importance of these microorganisms in our foods and the digestive tract. Her postdoctoral studies led to the discovery that probiotics are metabolically active in the intestine and responsive to dietary intake. Dr. Marco started her laboratory at UC Davis in 2008 and has built an internationally recognized research program on the topics of probiotics, fermented foods, and dietary fibers effects on the gut microbiome. Dr. Marco received the American Society for Microbiology Distinguished Lecturer award in 2012. Recently, she founded the ongoing Gordon Research Conference series on Lactic Acid Bacteria. She is the incoming president of the International Scientific Association for Probiotics and Prebiotics (ISAPP) and co-chair of the Live Microbes subcommittee for the Institute for the Advancement of Food and Nutrition Sciences. The boundaries of her research continue to expand as her lab applies genetic and ecological approaches to investigate how microbes in our diets and digestive tracts can improve human health.
About Pittcon
Pittcon is the world’s largest annual premier conference and exposition on laboratory science. Pittcon attracts more than 16,000 attendees from industry, academia and government from over 90 countries worldwide.
Their mission is to sponsor and sustain educational and charitable activities for the advancement and benefit of scientific endeavor.
Pittcon’s target audience is not just “analytical chemists,” but all laboratory scientists — anyone who identifies, quantifies, analyzes or tests the chemical or biological properties of compounds or molecules, or who manages these laboratory scientists.
Having grown beyond its roots in analytical chemistry and spectroscopy, Pittcon has evolved into an event that now also serves a diverse constituency encompassing life sciences, pharmaceutical discovery and QA, food safety, environmental, bioterrorism and cannabis/psychedelics.
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