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The science of fermentation

The range of fermented ingredients—from red yeast rice extract and coenzyme Q10 to wine and probiotics—is limited only by the imagination and physical laws of nature (and operating cost). What’s the potential of these ingredients for enhancing health and what finished products will they form? Here, Bob Hutkins, PhD, professor of food science at the University of Nebraska-Lincoln, dishes on what the future of fermentation may hold.

Q: What advantages does fermentation offer over conventional sources of nutritious ingredients?

A: In ancient times, fermentation was one of the main ways foods could be preserved, and even though preservation is still an important property, there are now many other ways to do it. However, fermented foods have other important advantages. For one thing, they have sensory properties—flavor, aroma, appearance and texture—that are often dramatically different from the starting material (think Roquefort cheese compared to milk). Fermentation also enhances the functionality of otherwise ordinary ingredients—not only does adding the right microorganisms to a simple flour-water dough help create a crusty baguette, but fermented sourdough can be used to make rye and other flours more amenable to bread making. Likewise, the unique flavors and intoxicating properties of wine, beer and other alcohol can only be achieved by fermentation.

Q: Do fermented foods offer enhanced nutrition?

A: Fermented foods have many important micronutrients. For example, wine contains several polyphenols, such as resveratrol and flavonoids, which are thought to reduce cardiovascular disease. Tempeh, a fermented-soybean product that originated in Indonesia, contains vitamin B12. While you can obtain resveratrol or B12 from a pill, it seems to me that the best way to deliver these nutrients is naturally via fermented food. Also, many fermented foods—particularly yogurt, unheated sauerkraut and kimchi—contain lactobacilli and other bacteria that can contribute to intestinal health.

Q: What have you discovered in your probiotics research?

A: Our research is focused on factors that influence the ability of probiotic bacteria to persist in the intestinal tract. A common misperception is that if a person consumes a probiotic, it always survives digestion and reaches the colon in a live and viable form. Unfortunately, this is not necessarily the case, and even if the organism does manage to survive the trip, there is no guarantee that it will be able to compete successfully with the trillions of bacteria that already reside in the colon. If, on the other hand, that probiotic was provided with a nutrient—a prebiotic—that it alone (or almost alone) could utilize and that its competitors were unable to efficiently use, then the probiotic would stand a much better chance of surviving.

Our work has shown that metabolism of prebiotics by probiotic bacteria is not a universal trait. Rather, the genes encoding for the relevant metabolic pathways are present in some probiotics and absent in others. There also is variation between different strains of the same species with regard to the route by which a prebiotic is metabolized. Differences in how different strains ferment prebiotics may also have implications with regard to how effective the prebiotic ultimately will be.

Q: Which probiotic strains best match which prebiotic fibers?

A: There is an array of prebiotics in the marketplace, ranging from the short-chain fructooligosaccharides (FOS) and galactooligosaccharides (GOS) to the longer-chain polysaccharides such as inulin and resistant starch. In one study, we showed that a particular strain of Lactobacillus paracasei grew very well on FOS and inulin but poorly on GOS, whereas a strain of Lactobacillus acidophilus grew well on GOS but not at all on FOS or inulin. Ultimately, this work speaks to the issue of compatibility—that is, if manufacturers formulate a food or supplement to contain both probiotics and prebiotics— a synbiotic—there should be experimental evidence to show that the probiotic can ferment that prebiotic.

Q: Prebiotics seem to be riding the coattails of probiotics. Are prebiotics effective alone?

A: It is worth noting that while the synbiotic approach has considerable merit, people may already harbor bifidobacteria and lactobacilli in their GI tract that will respond to prebiotics. In addition, prebiotics may also have an altogether separate benefit—their ability to inhibit pathogenic bacteria from adhering to intestinal cells.

Q: What do you think is the outlook for probiotics?

A: Obviously, there are more and more probiotic strains being introduced into a wide assortment of foods. Although probiotics must meet a number of important criteria—high numbers, viability, safety, survival through the digestive system—the main scientific issue, in my opinion, is validating that the probiotic strain provides a clinically proven health benefit. A lot of strains have good in vitro data and can be packaged to deliver high numbers of viable cells, but human feeding studies, with the outcomes published in scientific journals, are the ultimate test. Nonetheless—and this shows how much the field has advanced in recent years—there are now quite a few strains and probiotic products for which reasonable data exist to support health claims.

Q: Everyone wants probiotics integrated into foods, but has the research definitely validated specific health effects?

A: There are trillions of bacteria that live in the human intestinal tract, most of which can’t be grown in the laboratory. It is now possible, using high-throughput DNA sequencing technologies, for scientists to identify most of those bacteria and to assess the changes that occur when subjects consume probiotics or prebiotics, or simply change diets in other ways. There are also sophisticated analytical tools that can be used to detect metabolic changes or the appearance of disease biomarkers or immune system effectors that form under those same conditions. These new tools will not only influence the probiotics field, but, now that the intestinal microbiota has been shown to affect not only intestinal diseases but also obesity, diabetes and other systemic diseases, they also have the potential to have a much broader impact on our understanding of health and disease.

Q: Is it fair to say that not all probiotics are created equal?

A: It is important to note that health benefits are strain-specific. That is, while a given strain may be effective, for example, at reducing irritable bowel syndrome symptoms, that same strain may have no impact on other health issues. So while there are numerous strains in the probiotics marketplace, it may well be that those strains that can “prove” themselves with documented health benefits will be the ones that become accepted by the medical community and ultimately by consumers.

Todd Runestad is science editor of Functional Ingredients magazine.

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