Intro to prebiotics, probiotics and synbiotics

by E.J. Pyler and L.A. Gorton
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Cheese fillings for these snack cracker sandwiches contain probiotics.
 

Humans cannot make nutritional use of dietary fiber, but some of it is fermented, or digested, by microorganisms in the body’s gastrointestinal tract, specifically, the lower intestine. Such probiotic microbes (primarily Bifidobacteria, previously designated Lactobacillus bifidus) release metabolic by-products used by the human body for energy. Thus, dietary fiber is not completely calorie-free (Ranhotra and Gelroth 1985).

Probiotics, which means “for life,” was first used to describe growth-promoting factors produced by microorganisms, and the term was chosen deliberately to contrast with “antibiotic.” Today, it is applied to live microorganisms that confer a health benefit to the host (FAO/WHO 2001). Probiotics can be consumed as dietary supplements that contain beneficial bacteria or yeast. Probiotics offered for food use are highly specialized strains of Lactobacillus helveticus, L. rhamnosus, Bifideobacterium longum and, most recently, L. casei.

Like many bacteria, probiotics are heat sensitive, making them difficult to add directly to baked foods. Protected by encapsulation, however, they are earning a place in snack bars, muffins and similar foods.

Encapsulation makes probiotics more resistant to acidity, compression and shear. As encapsulation media, lipid materials with high melting points provide low moisture conditions and an anaerobic environment for probiotics. Chocolates containing coated probiotics are a good vector for probiotic addition because they does not require much additional processing and can be added to finished products in several ways (Kopp 2005).

Soy peptides, whey protein and dietary fiber make good encapsulation materials, too. Anal and Singh (2007) added hydrocolloids such as alginate, chitosan, carboxymethyl cellulose, carrageenan, gelatin and pectin to the list of potential encapsulation materials. They suggested that trehalose, a trisaccharide with known water-controlling properties, may be added to the coating to improve bacterial survival in processing conditions.

Prebiotic, as a term describing ingredients added to food, was introduced in 1995 by exchanging the suffix “pro” for “pre,” which means “before.” Prebiotics are defined as nondigestible food ingredients that may beneficially affect the host by selectively stimulating the growth and/or the activity of a limited number of bacteria in the colon. Thus, to be effective, prebiotics must escape digestion in the upper gastrointestinal tract and be used by a limited number of the microorganisms comprising the colonic microflora. Prebiotics are mainly oligosaccharides, and because they stimulate the growth of bifidobacteria, sometimes they are also referred to as bifidogenic factors. This definition more or less overlaps with that of dietary fiber except for the specificity for certain microbes (Gibson and Roberfroid 1965).

In other words, probiotic organisms ferment prebiotic materials to yield compounds including short-chain fatty acids (SCFA) that are beneficial to human health.

Dietary fiber is a prebiotic. So are some hydrocolloids and carbohydrates. Resistant starch has excellent prebiotic properties and is well tolerated by the body as well, causing considerably less side effects than other fermentable fibers.

Synbiotics are foods that combine probiotics and prebiotics. Since the term alludes to a combination of the activity of both, it should be reserved for products in which the prebiotic ingredient compound specifically favors the probiotic bacterial strain used in the product. For example, a product that contains the prebiotic oligofructose and a probiotic bifidobacteria would fulfill the definition.

Japan’s unique Foods for Specified Health Use (FOSHU) category came into effect in 1993, and nearly 70 different items have qualified, based on a list maintained by Japan’s Department of Health of approved foods and ingredients for which enough scientific evidence supports their health claims. The FOSHU list of acceptable ingredients includes several probiotics and prebiotics, and many of the FOSHU foods now on the market in Japan contain prebiotics; however, no foods containing probiotics have yet been approved.

Formulating with prebiotics is usually a balancing act between adding enough to achieve the nutritional properties without negatively impacting the sensory characteristics of the finished product. Doughs can be sticky and difficult to machine. Fiber typically absorbs a large amount of moisture, so formulators must account for this not only in the formulation’s water level but also in increased baking times and temperatures.

Also, some materials such as inulin may be hydrolyzed slightly by yeast enzymes. The best choice for yeast-raised products would be a high-temperature-process inulin, which also allows controlled water uptake in high-fiber bread with improved dough handling.

Because probiotics often release gases as by-products of their fermentation, excessive fiber in a formulation can run the risk of gastrointestinal discomfort (bloating). A good guideline is to stay within “good source” and “excellent source” parameters for fiber, or 2.5 to 5 g per serving.

 

References:

Anal, A.K., and Singh, H. 2007. Recent advances in microencapsulation of probiotics for industrial applications and targeted delivery. Trends in Food Sci. Tech. 18 (5): 240.

FAO/WHO. 2001. Health and Nutritional Properties of Probiotics in Food including Powder Milk with Live Lactic Acid Bacteria. Report of a Joint Food and Agricultural Organization of the United Nations / World Health Organization Expert Consultation on Evaluation of Health and Nutritional Properties of Probiotics in Food Including Powder Milk with Live Lactic Acid Bacteria. Published online at www.who.int/foodsafety/publications/fs_management/en/probiotics.pdf.

Gibson, G.R., and Roberfriod, M.B. 1995. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J. Nutr. 125 (6): 1401.

Kopp, J. 2005. Delivering health in unconventional ways — using probiotics and enhanced yeast. Proc. Am. Soc. Baking 81: 205.

Ranhotra, G., and Gelroth, J. 1985. Dietary fiber. AIB Tech. Bull. 7 (10).

More on this topic can be found in “Baking Science & Technology, 4th ed., Vol. I,” Page 376, by E.J. Pyler and L.A. Gorton. Details are in our store.

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