The Path to Improved Gut Health

As a digestive-system aid, yogurt is no stranger to American consumers, and now kefir, a cultured-milk product, is gaining converts. Traditionally, both contain probiotics, live microbial cultures that not only contribute to intestinal comfort, but to long-term health of the gut and the entire body. As the true value of probiotics is starting to be realized, the microorganisms as part of the food systemas well as the fuel that makes them thriveare being studied.

Good guys in the gut

A joint FAO/WHO Working Group in 2002 defined probiotics as live microorganisms which when administered in adequate amounts confer a health benefit on the host. This can include bacteria and other organisms like yeast.

Consumers who know about probiotics generally think about their positive impact on gut health, says Mary Ellen Sanders, Ph.D., consultant, Dairy & Food Culture Technologies, Centennial, CO. But the benefits are being shown to range more broadly than that, including immune support.

According to the Dannon Probiotics Center at www.probioticscenter.com, more than 400 species of bacteria call our gastrointestinal, or GI, tract home. Not all provide benefits. With probiotics, the fi rst line of defense is pathogen inhibition. Some microorganisms help create an inhibitory environment by producing short-chain fatty acids, SCFAs, thus reducing pH; and by making specific binding sites and nutrients unavailable to the unwanted organisms. Further, beneficial bacteria stimulate the mucin lining the intestine, improving its barrier properties. Finally, probiotics support GALT, or gut-associated lymphoid tissue, which produces and stores immune cells.

Beyond the prevention of diarrhea, irritable bowel syndrome and other intestinal ills, the effects of gut health resonate throughout the body. An improved barrier between the small intestine and the rest of the body may reduce the severity of an allergic response. Probiotics effects on certain cancers, blood cholesterol levels and autoimmune diseases is also being studied.

Probiotic decisions

Which of those 400 species should be added to foods? Yogurts standard of identity specifies that two microorganisms, Streptococcus thermophilus and Lactobacillus bulgaricus, be present in the culture. Although not considered probiotics, they create a vehicle for the inclusion of probiotic and prebiotic ingredients. The number of probiotic colony forming units (CFU) per gram to impart a health benefit varies from 108 to 1010 depending on the study.

The most common probiotics are Lactobacillus and bifidobacteria strains, including L. acidophilus, L. paracasei, L. casei and Bifidobacterium animalis, also known as Bifidus regularis. Yeast can also act as a probiotic. Saccharomyces cerevisiae subtype boulardii might improve antibiotic-associated diarrhea. Different probiotic strains provide different benefits, depending on their function in the gut. Sanders recommends a combination to impart a range of health benefits.

Yogurt that carries a contains live cultures label must have 108 viable lactic acid bacteria at the time of manufacture. However, it says nothing about the numbers of probiotics contained in the product through the end of shelf life or if the specific probiotics present have been shown to have a health effect. These yogurts are certainly a source of live bacteria in the diet, but may not have proven benefits, says Sanders.

Not all bacteria with the same taxonomic reference will impart the same benefit, notes Peter Budde, product group manager, human health and nutrition, Chr. Hansen, Inc., Milwaukee, WI. For instance, not all L. acidophilus organisms have the same characteristics or benefits, he says. In fact, they are usually quite different. Therefore, in lieu of the taxonomic reference, specific strain designations are becoming a more-prevalent way to convey the inclusion of a specific probiotic strain within a producte.g., L. acidophilus LA-5, L. rhamnosus GG, Bifidobacterium lactis BB-12. In this manner, a probiotic supplier can assure consumers that a specifically documented strain is present in the product.

The criteria for selecting the ingredient form depend on use. Freeze-dried cultures are dried to a near-dormant state, so can be stored at warmer temperatures, -20°C instead of -40 to -60°C, says Terri Rexroat, global product manager, lactic cultures, Cargill Texturizing Solutions, Waukesha, WI. Therefore, they are more versatile for regions with difficult logistics and/or lack of freezers. Frozen cultures require colder shipping and storage, so they are more expensive to handle. However, they are faster to ferment and generally thought to be more consistent than freeze-dried cultures.

Its important to minimize air incorporation and control pH and temperature. Most probiotic strains are intolerant of oxygen, Rexroat says, so keeping them viable can be difficult since, during food manufacture, agitation and pumping steps are usually required. She suggests minimizing shearing in yogurt manufacture by using minimal agitation, adding the culture close to the mix surface in the tank, and using positive displacement rather than centrifugal pumps during packaging.

Acid is another enemy of probiotics; therefore, maintaining pH greater than 4.0 will help their viability, continues Rexroat. Some applications, such as fruit juice, are typically more acid and, as a result, probiotic levels will be lower. But if the process is otherwise gentle, survival can be surprisingly high. She recommends not subjecting cultures to temperatures above 120°F.

High-pressure processing, HPP, can extend yogurt shelf-life without heat. We can include heat-sensitive ingredients in commercially sterile foods and drinks, such as live probiotic bacteria or yogurt with big chunks of fruit, or extend the shelf life of cultured products, says Nigel Little, new options manager, Fonterra Co-operative Group Ltd., Auckland, New Zealand. He notes that, in yogurt, good bugs, such as the probiotic B. lactis, will survive HPP, while bad bugs like yeasts and molds are killed.

Some probiotic bacteria can add flavor. In yogurt, bifidobacteria contribute a pleasant, mild flavor, because they metabolize lactose differently than the usual yogurt bacteria, says Rexcoat. However, they need to be present at a sufficient level and, in addition, the yogurt pH should be above pH 4.0 for these flavor notes to be apparent.

Prebiotic tips

Prebiotics are simply ingredients that support the growth of a healthy microflora in the gut. But to be available for fermentation there, fermentable material must actually reach the gut.

Gums give product designers the opportunity to leverage functional propertiescontrol texture, create freeze/thaw stability, etc. while providing health benefits. In beverages or dressings that require suspension by a gum that must withstand acid or processing, xanthan provides the solution. In applications that need a high soluble- fiber level, lower-viscosity products such as gum arabic and hydrolyzed guar fit the bill.

Inulin, a polysaccharide, is widely used as a prebiotic. According to Juliana Zeiher, ingredient technologies manager, GTC Nutrition, Golden, CO, there are three major categories of prebiotic products: short-chain fructooligosaccharides (scFOS), inulin and oligofructose. To understand the role of prebiotics in promoting health, one must first learn about the different types, their origin, structure and function. This is the foundation that will support good choices for formulators and consumers alike.

Fructooligosaccharides (FOS) has been used almost universally when describing the prebiotic category, notes Zeiher. However, this label is not entirely accurate, and the general misunderstanding has occurred specifically because the differences between the three prebiotic categories were previously not well understood, she says. NutraFlora scFOS is a specific, defined mixture of glucose-terminated fructose chains with a maximum chain length of 5 units, and 95% pure active prebiotic. It is derived from sugar cane by a natural fermentation process. Oligofructose, a mixed FOS, is the enzymatic hydrolysis product of inulin. It consists of mixed glucose and fructose-terminated chains, varying in length from 2 to 7. Inulin is not an FOS, because the majority of its chains exceed 10 units. This makes inulin a polysaccharide that has some prebiotic properties.

Inulin doesnt consist of one molecule: It is a mixture of linear fructose polymers and oligomers with the fructose units linked by beta (2-1) bonds and chain lengths of from 2 to 60 units. The IUB-IUPAC Joint Commission on Biochemical Nomenclature and the AOAC define oligofructose as fructose oligosaccharide containing 2 to 10 monosaccharide residues connected by glycosidic linkages.

The chemical structure and relative chain length of a prebiotic will determine how easily probiotic bacteria can use it, notes Zeiher. Where 10% of inulin will function as a prebiotic, scFOS is 95% active. She adds that oligofructoses fermentation profile differs from the other two ingredients, so it supports growth of different beneficial microorganisms.

Probiotics can provide unexpected benefits. New studies have indicated a clear link between the consumption of inulin and an increase in calcium absorption relating to increased bone mass and strength, says Maureen Akins, food scientist, TIC Gums, Inc., Belcamp, MD. Documented results indicate that by increasing production of short-chain fatty acids, a decrease in pH in the gut can be achieved, thereby increasing the solubility of calcium in these environments.

Inulin will break down in acidic conditions. Akins advises using inulin in foods with pH greater than 4.0. Low- and high-viscosity inulin ingredients are selected according to application. When altering an existing product formulation where you need to maintain current viscosity and mouthfeel characteristics, it is helpful to add a low-viscosity product that will not interfere with current product quality, she explains. Beverages, bars and yogurts would be good examples of products that can benefit from using a lower-viscosity inulin product. If I have a product that needs some texture modification, using a higher-viscosity inulin will help create a fuller mouthfeel while also increasing soluble-fiber content. Smoothie-type applications that may be lower in fat or sugar benefit from the additional mouthfeel obtained when using a higher-viscosity inulin product.

Polydextrose, a highly branched glucose polymer, has multiple application and health functionalities. It is slightly sweet and provides bulk to no- or low-sugar applications. The molecules complexity provides some viscosity, so polydextrose can serve as a fat mimetic in applications such as frozen desserts and nutritional drinks. We offer a unique version of polydextrose called Litesse® Ultra that is very neutral tasting, clear in color and sugar-free, says Donna Brooks, product manager, Danisco Sweeteners, Ardsley, NY, noting that the prebiotic fiber delivers 1 kcal per gram.

Resistant starch resists absorption in the small intestine. When included as a health-promoting dietary fiber, Hi-maize® 260 offers numerous options to food manufacturers, as it has more than 100 published studies demonstrating health benefits and can substantiate many different structure/function claimsi.e., Helps maintain healthy blood sugar levels, says Rhonda Witwer, business development manager of nutrition, National Starch Food Innovation, Bridgewater, NJ. As scientific studies have shown that different resistant starches behave differently in the body, these studies cannot be applied to other types or sources of resistant starch. She explains that a key attribute of natural resistant starch is that it ferments to produce more SCFA butyrate than other prebiotics. Because butyrate is the preferred energy source of healthy colon cells, this produces a physiological difference in health benefits for different types of dietary fiber, she says.

Resistant dextrins also act as prebiotics. They are derived from several sources, including wheat, corn and tapioca. Nutriose®, a resistant corn dextrin, is 100% soluble, clear and neutral flavored, with a smooth texture, and is stable to heat, acid and shear, notes Deborah Dihel, Ph.D., business development manager, National Starch. The dose tolerance is 45 grams per daymore than the FDA recommends for a daily fiber consumption (28 to 35 grams per day)so a consumer can get all of their daily fiber from it without fear of digestive discomfort. It doesnt contribute significant viscosity, making it suited to beverages.

Resistant dextrin has a very small molecular weight in comparison and is soluble in water, whereas resistant starches are still granular in nature and thus are insoluble in water, says Dihel. Therefore, resistant starches are typically targeted to low-moisture foods like breads, baked goods, etc. as a flour replacer. Resistant dextrins can be used broadly, but they do require some formulation changes when used at high levels in baked goods, because of the high solubility.

USDAs Agricultural Research Service found that the pecticoligosaccharides in orange peel have a prebiotic effect, stimulating the growth of bifidobacteria and Eubacteria (Applied and Environmental Microbiology, 2005; 71:8,383-8,389). Typical fibers hold water, but easily release this water over time and/or during various treatment conditions, says Brock Lundberg, vice president of technology, Fiberstar, Inc., Willmer, MN. The companys pectic-oligosaccharide ingredient has a high internal surface area, which exposes many hydrogenbonding sites for tightly binding water without releasing it.

Two sweetening prebiotics tagatose and lactitolhave been granted GRAS status by FDA. Lactitol, a sugar alcohol that is 40% as sweet as sucrose, contributes 2 kcal per gram. Lactitols bulk and reduced sweetness allow it to be combined with high-intensity sweeteners. Its fermentation in the colon promotes gut health by supporting good bacteria, reducing pathogens and reducing pH. Tagatose, a low-calorie sweetener that is slightly less sweet than sucrose, contributes 1.5 kcal per gram. Unlike sugar, only 15% to 20% of tagatose is absorbed in the small intestine; the remainder is available as a prebiotic in the colon.

The combination of probiotic and prebiotic ingredients is referred to as synbiotic. Probiotics and prebiotics can provide complimentary benefits in products. One advantage to prebiotics is that you dont have to worry about keeping them alive. One advantage to probiotics is that you know what benefits the specific strain you are using should provide. So both can be used for the specific benefits they have been shown to impart. says Sanders. Combinations of polydextrose, lactitol and FOS cause growth of different bacterial populations and short-chain fatty acidsin a simulated gut (Applied and Environmental Microbiology, 2004; 70(8):4,505-4,511).

Products for digestive health are established in Japan and Europe, and are just starting to show up on labels in the United States. Perhaps well start to see flavors like Blueberry Bifida or Strawberry Saccharomyces in the near future. 

Karen Grenus, Ph.D., has eight years combined experience in applied research and product development in the area of dry blends for savory applications. She holds a doctorate from Purdue University in Agricultural and Biological Engineering.