Proven effectiveness is important when choosing prebiotics. “Every fiber is not prebiotic,” notes Lisa Sanders, nutrition scientist, Tate & Lyle, Decatur, IL. “The fibers that tend to be prebiotic are the ones that are fermentable.” Similarly, all prebiotics do not stimulate all probiotic bacteria. As an example, she says, “resistant starch has a very large particle size, so it can only be fermented by particular bugs. But the metabolites that those bugs produce from fermenting the resistant starch can then be used as food by other bacteria in the colon. So there’s this cross-feeding that can occur.”
Putting prebiotics to the test
Manufacturers are devoting increased effort to identifying probiotic-prebiotic combinations that generate the best effects. “It is not clear which prebiotic carbohydrates are the most-suitable substrates for selective growth of specific strains,” says Donna Brooks, regional director, Danisco Texturants & Sweeteners, Elmsford, NY. “But, for the time being, in vitro tests have been conducted to determine the functional activity of various prebiotic carbohydrates combined with some probiotic strains. The results indicate that some associations, such as combinations of galactooligosaccharides and some Lactobacillus acidophilus or Bifidobacterium lactis, are best-suited for a synergistic effect.” And, she notes “encouraging results” from a clinical study, conducted at Danisco’s health and nutrition facilities in Finland, on the synergistic effect between the company’s Dophilus probiotic and the prebiotic sweetener lactitol.
In explaining her company’s approach to evaluating prebiotic efficacy, Sanders says, “we started with in vitro tests looking at specific bugs in the culture system and feeding them our fiber to see if they grow when fed that particular prebiotic.” The results showed “some very prebiotic effects” for the company’s resistant starch and soluble corn fiber, which led them to the next step: human studies. “We would feed humans the resistant starch or soluble corn fiber, and we would measure in the fecal material the different bugs that were promoted as a result of feeding the resistant starch and soluble corn fiber,” she says. Preliminary dosages to produce a prebiotic response worked out to about 10 to 12 grams per day of resistant starch or soluble corn fiber. However, “the dosing part is still under investigation,” she says. “Whether the response will increase the more that you give, we don’t know yet. But we do have some studies underway that are looking at higher doses.”
Prebiotic inulin and oligofructose has also come in for investigation, according to Joe O’Neill, executive vice president of sales and marketing, Beneo-Orafti, Morris Plains, NJ. “In vitro tests have found that Orafti inulin and oligofructose are excellent selective growth media and energy substrates for healthy bifidobacteria,” he says. He singles out their effect on bifidobacteria in particular as a key advantage. “Bifidobacteria prevent colonization of the gut by pathogens by creating a barrier effect, and also produce a range of short-chain fatty acids that lower the overall pH in the digestive system,” he says. “This lowering of the pH of the colon has been shown to facilitate increased calcium and magnesium absorption in the body.” According to human intervention studies, regular intake of this inulin and oligofructose increases the gut’s population of beneficial bifidobacteria five- to tenfold, while reducing the level of harmful organisms like clostridia.
Banking on synergism
Egged on by prebiotics’ stimulative effects on probiotics, manufacturers have aimed to parlay the relationship into a whole new category of functional food: the “synbiotic.” While no official definition for such products yet exists, “when both probiotic cultures and prebiotics are added to foods, the two work in synergy and are referred to as synbiotic,” O’Neill says. “The concept of synbiotic foods developed in Europe and was used as an opportunity to differentiate and market cultured dairy products.”
The category is still in its infancy, both in terms of public awareness and scientific acceptance. The main question remains whether or not the interaction between probiotics and prebiotics in a single food is truly synergistic—as in more than the sum of its parts.
Mary Ellen Sanders isn’t so sure. “I have not seen strong evidence of that,” she says. “What we see sometimes are additive effects—you have a probiotic alone, a prebiotic alone, you put them together, and you get more than each by itself. But you don’t necessarily get more than the sum total.”
Researchers continue to look for the synergies, however, and O’Neill is bullish on their prospects. “For instance, studies have shown that prebiotics exert a stabilizing and protective impact on probiotics in products from manufacturing through shelf life all the way to the digestive tract,” he says. In one study, researchers supplemented Lactobacillus rhamnosus or Lactobacillus casei yogurts with 3% oligofructose in two forms. They tested the products at 10-week intervals for culture viability during shelf life, while also using a model in vitro digestive system to determine viability after consumption. Results showed that, at 10 weeks, both forms of oligofructose displayed a protective effect on the probiotics with no change in viability. The prebiotic yogurt processed through in vitro digestion showed no significant difference in L. rhamnosus cell counts, compared with a 36% decrease in the control, and the prebiotic L. casei yogurt saw a 5% decrease in culture viability after in vitro digestion, vs. a 19% decrease in the control. The conclusion, O’Neill says, is that the prebiotics “protect probiotics during both storage and digestion.”
Perhaps more intriguing is how synbiotic foods protect us. Puzzling out those benefits is the goal of the SYNCAN Program, an EU-funded research project that brings together scientists from six different countries to test the hypothesis that prebitoics and probiotics in combination protect the gut from the DNA changes that trigger colon cancer. One study looked at patients treated for colon cancer, as well as healthy subjects who had intestinal polyps removed. The subjects received either a placebo or a daily synbiotic supplement combining an Orafti prebiotic with two probiotic cultures. After 12 weeks, the subjects in the synbiotic group saw reductions in colon-cancer risk markers, normalization of cell turnover, and a 60% decrease in mucosal DNA damage, with risk reduction particularly strong in the polyp patients. “The dramatic risk reduction seen in the synbiotic group coincided with changes to the composition of gut bacteria that favored protective species, such as Bifidobacterium and Lactobacillus,” O’Neill adds. “These changes happened within a few weeks, showing that synbiotics can deliver immediate, as well as long-term, benefits.”
Formulation fundamentals
Though the jury may be out on synbiotics’ staying power, manufacturers are working on formulations while they wait for a consensus. The key points to keep in mind are that the synbiotic combination should suit the application, the dosage should be effective and tolerable, and the whole getup should stay stable during and after processing.
Brooks suggests working with prebiotic ingredients that don’t get in the way of color, texture or flavor. A product like Danisco’s refined polydextrose has “virtually no taste and is colorless in solutions,” she says, making it easy to incorporate into a range of systems. “Lactitol, a polyol, is equally easily incorporated into food matrices, although some local legislation may limit its use in beverages,” she adds.
Being soluble, soluble corn fiber gives beverage makers an opportunity to get on the bandwagon, Sanders says. “It can be put into a water and you can’t even tell that it’s in there.”
Inulin and oligofructose are also formulation-friendly, showing up in everything from refrigerated orange juice to nutritional bars to cereal. “Technical benefits include bulking, sugar reduction, calorie reduction and the masking of high-intensity sweeteners,” O’Neill notes. “Lately, Orafti has introduced liquid syrups for ease of use and as a low-cost fiber-delivery option.”
As far as dosing is concerned, you want enough prebiotic to stimulate the bugs, but not so much that it overloads consumers with fiber. Brooks says that human intervention studies have determined a comfortably low, effective, prebiotic dose of 4 grams per day for her company’s fiber. “The tolerance for lactitol is on par with other prebiotics, such as fructooligosaccharides and inulin,” she adds.
Fortunately for all involved, most prebiotic fibers are reliably stable in formulation. Inulin and oligofructose can break down in acidic conditions at room temperature, but generally do well under refrigeration. “Prebiotics are usually stable during product shelf life and easily incorporated into any food application,” Brooks says. “Any limitations are likely to depend on the application of the probiotics.”
That’s why, as the experts have said all along, the proof is ultimately in the product. Case-by-case assessments of pre- and probiotic composition and functionality—after production, during storage, even after consumption—are the only proof we have to convince the public to sign on. “Again, that’s why it’s so important to do the studies,” says Sanders. “At the end of the day, that’s the sum total of all of these factors: the host factors, the survival factors, the microbial factors. And at the end of the day, does it ultimately have an effect?”
Kimberly J. Decker, a California-based technical writer, has a B.S. in Consumer Food Science with a minor in English from the University of California, Davis. She lives in the San Francisco Bay area, where she enjoys eating and writing about food. You can reach her at kim@decker.net.
Probiotic Products Multiplying
The friendly bug boom is predicted to continue as research increases and health-conscious consumers become more aware of probiotics’ benefits. According to a 2008 report by Global Industry Analysts, Inc., San Jose, CA, “Probiotics: A Global Strategic Business Report,” the global probiotics market is forecast to reach $20 billion by 2010.
The company points out that Asians and Europeans lead the way in embracing these products, but the rest of the world is catching up quickly. In fact, Europe has the largest, fastest-growing market, with revenues of approximately $5.7 billion in 2007. Germany represents the largest market, and the United Kingdom has the fastest growing market, increasing at a compound annual growth rate (CAGR) of around 14%. The second-largest market is the United States, with sales expected to reach $4.6 billion by 2010.
The report identifies two potential barriers to growth: consumer concerns about GMO cultures, and companies that put forth health claims that are misleading and lack scientific evidence.
Digestive Health: Not Just for People
Humans aren’t the only ones who benefit from enhanced intestinal flora. Animals can, too.
Agricultural Research Service (ARS) scientists at the Poultry Production and Product Safety Research Unit in Fayetteville, AR, identified probiotics with the potential to protect live chickens from Salmonella, Campylobacter and other pathogens that cause foodborne illness, plus allow the birds to grow more efficiently.
Using competitive exclusion―where the “good” bacteria successfully compete with the “bad”—the scientists fed probiotics to newly hatched poults, when they are most susceptible to infection. These probiotics occupy sites in the young birds’ intestinal tracts and reduce the opportunity for pathogenic bacteria to become established. The team has screened more than 4 million intestinal isolates to identify several promising probiotic combinations. The University of Arkansas and ARS have filed a patent on the selection techniques.
ARS researchers found oligosaccharides provide prebiotic advantages when used as feed additives for pigs and chickens. They found the compounds aid probiotic organisms in unlocking minerals, vitamins and other nutrients, as well as making the animal’s colon less hospitable to the pathogens, such as Salmonella and Escherichia coli, that can contaminate meat products and cause human illness.
Chemist Greg Cote, with ARS Bioproducts and Biocatalysis Research Unit, Peoria, IL, co-developed these oligosaccharides with Scott Holt, an associate professor with Western Illinois University’s Department of Biological Sciences, using a microbial enzyme, alternansucrase, to catalyze a series of reactions that convert sugars into different kinds of oligosaccharides. Some of the resulting oligosaccharides encouraged growth of Bifidobacterium, Lactobacillus, Bacteroides and some enterococci bacteria, but not of pathogens such as Salmonella, E. coli or Clostridium perfringens. ARS patented the technology in 2007.
— Lynn A. Kuntz