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Originally Published NO June 2010
Gritty. Gloppy. Cardboard. These are just a few of the words consumers associate with the mouthfeel of fiber.
The concept of fiber has changed dramatically over the last 40 years. Fiber used to be thought simply as bulk material or roughage, food consumed to help one keep regular or as a laxative to relieve constipation. Through years of research and study, the science behind fiber has evolved dramatically. The more contemporary view of fiber is as a nutritional ingredient-seen as a necessary part of a balanced diet and a tool to aid digestive health.
As clinical studies have advanced knowledge of the nutritional benefits of consuming fiber, new processing methodologies have likewise evolved the physical attributes of fiber ingredients, with profound implications for food manufacturers and consumers alike.
To understand the evolution of fiber ingredients, it is necessary to understand how fiber is classified. Commonly, industry classifies fibers based on solubility in water. Insoluble fibers include wheat and corn bran, cellulose, and resistant starches, among others. Insoluble fibers generally function to move bulk through the intestines to promote regular bowel function and to relieve constipation. The use of insoluble fibers is often limited, depending on the desired application. While insoluble fibers are a natural fit in a category such as bakery goods, they are generally unsuitable in beverage applications and may need to be further physically processed so as not to affect taste and texture.
Soluble fibers can be subdivided into high-viscosity and low-viscosity fibers.
Examples of high-viscosity soluble fibers include pectin, xanthan gum, and mucilage. These fibers have been used traditionally as rheology modifiers, emulsion stabilizers, and texturizers. Functionally, they do behave as a fiber in the body, as they are not digested in the stomach or small intestine. However, their use for fiber supplementation is limited in most applications due to their thickening effects at even low to moderate levels of inclusion.
Low-viscosity soluble fibers offer the greatest potential to the food formulator. In general, these fibers dissolve readily in solution, have high levels of fiber purity, and contribute minimal flavor or sweetness. In essence, they are "invisible fibers," because they can easily be added to products without impacting taste or mouthfeel.
For food manufacturers, achieving a balance of taste and nutrition is not always easy. Traditionally, food developers have played a zero-sum game over taste and nutrition-that is, to increase taste appeal, they would have to sacrifice nutrition, and vice versa. Low-viscosity soluble fibers offer a simple solution to this dilemma.
In general, there are few application limitations for these invisible fibers, which are used for several reasons, both nutritionally and functionally.
Nutritionally, fiber supplementation has obvious benefits. Invisible fibers can be used to enhance a food or beverage's fiber content, so that companies can make a "good source" or "excellent source" claim.
Another benefit is sugar reduction. High-intensity sweeteners have gained popularity over the last 15 years for their use in several reduced-sugar and sugar-free applications. Because high-intensity sweeteners offer several hundred times the sweetness of sucrose, they are often used in smaller amounts-and thus are unable to add the same bulk that sugar would generally provide. Invisible fibers can be used in concert with high-intensity sweeteners to provide an ingredient solution with appropriate sweetness and bulk. The benefits are reduced sugar, increased fiber, and reduced calories, because low-viscosity soluble fibers offer less than the 4 cal/g that carbohydrates provide.
Another nutritional benefit is that most low-viscosity soluble fibers offer prebiotic effects. The average adult body contains between 1 × 1014 and 2 × 1014 bacteria, roughly ten to 20 times the number of cells in the body. Our bodies have evolved to contain an immense variety of bacteria, some good and some bad. When the populations of bad bacteria increase, problems such as constipation, diarrhea, and encephalopathy occur. One way of suppressing the bad bacteria is by using probiotics, or live strains of the good bacteria, that can be delivered to the gut to colonize and grow. Because efficacy and stability are common problems with probiotics, prebiotic fibers offer another solution. The goal of a prebiotic is to act as a substrate to help the good bacteria grow, changing the balance of microflora in the large intestine and leading to improved digestive health.
From a formulation viewpoint, invisible fibers can offer some texturizing benefits. In beverages, they can increase mouthfeel to make a smoother-tasting drink. In bakery goods, they can be used for partial fat substitution and sugar replacement. And in dairy applications, they can enhance organoleptic properties and add a feeling of creaminess.
Types of Invisible Fibers
There are several types of invisible fibers available to formulators. A brief description highlighting some of the key properties of each follows.
Resistant dextrins are a relatively new class of soluble fiber, derived from non-genetically modified corn or wheat starch, and consisting of glucose monomers linked by alpha and beta bonds. Resistant dextrins have a higher molecular weight than most of the low-viscosity soluble fibers, allowing them to have excellent stability when processing in acidic, high-thermal, and high-shear conditions. Resistant dextrins show prebiotic effects and offer excellent digestive tolerance, demonstrating minimal side effects at 45 g/day and showing no laxation at 100 g/day. Because they are spray dried and agglomerated, resistant dextrins exhibit superior functionality for beverages, with quick wetting, no clumping, and a high rate of solubility.
Polydextrose is a highly branched synthetic polymer created by the random polymerization of glucose and sorbitol. Polydextrose has been used commercially since the 1980s. At only 1.0 kcal/g, it is one of the best soluble fibers for calorie reduction. One of the more popular uses for polydextrose is in frozen desserts, as an additive for increased freezing-point depression. Polydextrose also has a very high tolerance, with a mean laxative threshold of 90 g/day.
Inulin and FOS (fructooligosaccharides) belong to the same class of fructose-based fibers known as fructans, with linkages between fructose monomers usually ending with a terminal glucose. Fructans can be derived synthetically but are often extracted from natural sources of chicory root or Jersualem artichoke. For this reason, the term "chicory root extract" is often used in labeling. Fructans are known for their excellent prebiotic effects, often used in medical nutrition to boost microflora after a broad course of antibiotics. However, fructans suffer in terms of digestive tolerance (fermentation of fructans in the large intestine generates more gas than other fermentable fibers) and stability (FOS has shown evidence of breaking down in thermal processing and in acidic conditions). Nevertheless, fructans have a great range of functionality. The lower-molecular-weight FOS and inulins offer good overall invisibility. The higher-molecular-weight inulins, although providing less solubility and invisibility, have substantial fat-mimetic properties.
Resistant maltodextrins have been used for more than 20 years in industry. Structurally, they are similar to resistant dextrins but differ slightly in the percentage of specific linkages between monomer units and have a lower average molecular weight. In vitro studies with resistant maltodextrins show a slower fermentation rate compared to FOS, leading to enhanced dietary tolerance. Like resistant dextrins, resistant maltodextrins show good stability in the presence of heat and acids.
Different Needs, Different Fibers
When formulating, the key thing to remember is that there is no magic bullet in terms of a single invisible fiber to use in all cases. All of the low-viscosity soluble fibers have positives and negatives. Nutritional claims, consumption levels, and functionality are just a few of the factors to consider when choosing between the low-viscosity soluble fibers.
In summary, clearly, with the advent of new science and technology, food formulators have a larger toolbox to play with. For years, the central dogma was that when formulating healthy products, taste would be sacrificed. Low-viscosity soluble fibers, or invisible fibers, subvert this idea and offer both nutritional and functional benefits to food manufacturers and consumers alike.
Gloppy, gritty, cardboard-tasting fiber is a thing of the past.
Neelesh Varde, PhD, is business development coordinator for Roquette America (Keokuk, IA) and can be reached at firstname.lastname@example.org.