The Science Behind Probiotics and Prebiotics

Doses range anywhere from several hundred million colony-forming units, or CFUs, per serving to tens of billions. Determination is elementary. “Say you want a product that’s a shot-type beverage,” Bush explains. “Ultimately, you want to make immune claims. So you’re going to run a study that shows your product’s ability to bump the immune system; our clinical trial showed that a billion cells per day every day for 30 days had some effect on the immune system. So, because it’s designed to be a one-shot-a-day product, you would dose the shot so that, at the end of shelf life, you had a billion cells. If you’re going to have something that you may consume in multiple, maybe four, servings throughout the course of a day—let’s say it’s a tea—and you want to deliver the same effect, you just knock down the dose so you have 250 million cells per serving.”

Live and active

Bush believes transparency in labeling doses and the strains delivered not only empowers consumers, but benefits the category by buttressing its credibility. “We’re strong believers in saying what’s in there—the specific strain, the dose. And we’re not yet seeing a lot of companies saying how many cells are there in food. But, eventually, people should be saying that there are X number of cells at the end of shelf life.”

That assumes, of course, that X number of cells actually survive processing and digestion. “Probiotics are generally very sensitive to heat, pressure, shear, pH, water activity and a variety of other conditions found throughout many stages of a manufacturing process,” says Sean Farmer, founder and chief scientific officer, Ganeden Biotech. In addition, stomach acid, bile and digestive enzymes do a number on even healthy cells, let alone those weakened by processing or long residence in a dairy case.

But, notes Bush, “people who are in the business of probiotics know what the overage parameters are.” For a product with 10 billion cells at the end of shelf life, for example, “they may put 30 billion in at the beginning,” he says.

The take-home lesson according to Farmer is that “quality is more important than quantity. If the cells are not able to survive to colonize the host, even huge doses are not going to make any difference.”

That colonization needn’t occur in the colon. “If your target is to prevent dental caries,” Sanders says, “then no, they don’t have to survive stomach acid.” Probiotics that act on H. pylori don’t need to inhabit the colon either. “If you have a microbe that can be delivered to the stomach and do what it needs to do there,” she says, “do you need to isolate that from the feces? You don’t.”

Super bugs

Traditional formulations linked probiotics to dairy applications partly because dairy buffered the bugs’ ride through the stomach, and because refrigerated storage prolonged survival. But other reasons suit probiotics to dairy delivery, as well, including dairy’s healthful image; consumers’ comfort at seeing live and active cultures in dairy foods; and the fact that many of the same microbes that ferment dairy also colonize us, and many of those are probiotic. And, says Rexroat, “dairy products are often consumed on a daily basis, so they fit well with the daily-dose concept,” as the popular probiotic-shot concept exploits.

As probiotic suppliers tinker with strains and their manufacturing techniques, they open doors to “many new market areas, such as chocolate confectionery, fruit juices, breakfast cereals and more,” Steele says. Whereas water-activity restraints, pH limitations and the presence of antimicrobial agents once excluded probiotics from wider applications, companies are “developing advanced stabilization systems such as encapsulation or specific processing technologies to help handle some of these application issues,” she says.

It’s still a work in progress. Steele notes that “in evaluating multiple commercially available encapsulation technologies, no stability improvement has been noted to date in dry to intermediate-moisture systems.” Alginate systems, on the other hand, have provided some reported stability benefit in acid products, such as fermented yogurts. And Danisco, working with technology from the University of Wisconsin, has developed a freeze-drying process that “can provide specific strains with a 2-year shelf life at room temperature,” she says.

Sometimes, the bacterial strain itself improves its shelf life and viability. For example GanedenBC³⁰ (Bacillus coagulans GBI-30, 6086), a spore-forming probiotic, produces a protective layer that helps it survive manufacturing and human digestion to colonize the gut. Enclosed in its spore, the dormant bacteria withstand the rigors of processing, the supermarket and the consumer’s grocery bag. Once in the gut—their ideal growing environment—“they germinate and produce L+ lactic acid, which is a great form of lactic acid that helps lower gut pH,” Bush says.

This expands application options. While ready-to-eat cereal manufacturers once sprayed a topical probiotic solution onto their finished puffs, spore-forming probiotics allow you “to put the bacteria right into a dry food mix, mix it with your wet ingredients, run it through your dies to extrude it, and then stick it on the shelf and test its stability,” Bush says. “We’re able to grow the cells and enumerate the bacteria and get good survival through the process”—more than 85% viable cells post-processing in HTST milk, for example, and more than 80% in a hot-mixed granola bar.

This spore-forming probiotic is actually better suited to dry applications than to wet, too, to prevent premature germination. “Our bacteria allows us to do things that you can’t ordinarily do—dried products and baked products and products that involve reconstitution by the consumer,” Bush says. “We work fine and dandy in a hot tea made from a teabag.”

When live and active, the probiotic can survive a pH range of 3 to 12 and tolerate high-salt media—20% sodium chloride according to Farmer. “It’s very hardy as a vegetative cell,” he says. “The spores, obviously, are much tougher.”

Bug food

To keep probiotics vital, we shouldn’t overlook a factor perhaps even more obvious than salt levels, pH and processing conditions: the probiotics’ nutrition. Prebiotics—nondigestible dietary carbohydrates that selectively stimulate the growth or activity of beneficial colonic bacteria—are probiotics’ favorite foods.

When we eat a prebiotic, usually some form of fiber, it resists digestive breakdown and ends up in the large intestine, where it gives the microflora, particularly probiotic lactobacilli and bifidobacteria, something to eat. Proven-effective prebiotics include inulin and fructooligosaccharides, polydextrose, lactose derivatives such as lactulose and lactitol, granular RS2 resistant starch, and hydrocolloids like xanthan gum and pectin.