New Ways to Apply Fiber

Cellulose is a polymer of ß-D glucan units with 1,4 linkages with up to 10,000 monomers per molecule. Although its chemical structure is similar to some starches, it exhibits very different physical properties. Natural cellulose is found in plants. It is insoluble in water and non-digestible.

Hemicellulose is a category that is poorly defined. Compounds called water soluble "acid hemicelluloses" include gums, pectin and mucilages. Hemicelluloses consist of polymers of (-D 1,4 pyranosidic sugars with 50 to 200 monomers per molecule. Xylose, arabinose, mannose, glucose and galactose predominate. Cereal hemicelluloses, called pentosans, contain monomers of xylose and arabinose.

Pectins consist of complex mixtures of polysaccharides of partially methylated (-1,4-D galacturonic acid units. These have side chains that contain arabinose, galactose, xylose and rhamnose. Fruit pectins are hot water soluble.

Gums and mucilages are typically derived from plants and cereal grains, and they have varying levels of digestibility. Their structures also vary, but all are polysaccharides that contain several sugars with alternating monomer structures. For example, guar and locust bean gums are galactomannans, while gum arabic is an acidic polymer of galactose and rhamnose. Oat gum and barley contain significant levels of (-glucan.

Lignin is a non-polysaccharide polymer of aromatic plant alcohols. In plants, lignin holds the plant cell wall together, and helps prevent biochemical degradation and physical destruction of the cells.

Resistant starch (enzyme-resistant starch) is described as natural; the enzyme resistance results from the typical retrogradation of starch. The linear amylose polymer found in high-amylose starch forms orderly bundles that are so compact that digestive enzymes are unable to penetrate them. Resistant starch occurs naturally in unprocessed foods like bananas and lentils, and processed foods like bread, ready-to-eat cereals and cooled, cooked potatoes. High-amylose corn starches are typically used as the source for commercial resistant starches.

  Many fiber sources contain more than one of these component fibers. For example, sugar beet fiber contains approximately 73% total dietary fiber (TDF). This percentage is made up of 29% hemicellulose, 22% pectin, 18% cellulose, and 4% lignin. The sheer number of potential combinations of these components results in a wide variety of different physiological and functional effects. By the same token, not every fiber source has the same amount of total dietary fiber. Table 1 compares the approximate dietary fiber content of several commercially available fibers.

Go to the source

  Broadly categorizing fiber ingredients by their source, their method of processing, and whether or not they are purified fibers may also be helpful when discussing them.

Grain products. Usually the hull of the grain is the fiber source, but fiber can also come from other portions. Flaxseed may be used whole or milled, and fibers sourced from the cotyledon are available. Soy fiber may be sourced from the cotyledon. Grains are the most unrefined source of fiber; they typically include corn, oats, rice, soybeans and wheat bran. With the exception of corn bran (approximately 55% TDF), these sources have relatively low TDF.

Modified fibers. Bran and cotyledon-sourced cereal fibers receive minimal processing compared with the concentrated, modified fibers. For the most part, the modified versions also come from cereal grains, but they are categorized separately because they are so different. Typically, these fibers are noncaloric, contain 90% or more total dietary fiber, are very bland, and have a very light color. Water-absorption properties are typically improved.

  Various processes bring about these changes. One modified wheat-based fiber, UltraCel(tm), offered by Watson Foods, has been thermo-mechanically expanded to boost its water-absorption properties and to eliminate grittiness or dryness in the fiber. It contains around 70% TDF.

  Resistant starches and partially hydrolyzed guar gum are also included in this category, although there are exceptions to the general rule. For example, National Starch and Chemical's resistant starch, Novelose(tm), analyzes at 30% TDF and has 2.5 to 2.8 Kcal/gram. Sandoz Nutrition's partially hydrolyzed guar gum, Benefiber(r), contains 80% soluble fiber and has 4 Kcal/gram.

  Another physically modified fiber, Z-Trim, was recently unveiled by George E. Inglett of the U.S. Department of Agriculture's Biopolymer Research Unit, Peoria, IL. Physical shear creates a fine, white cellulosic powder that remains undigested and therefore has zero calories.

Cellulose products. Most concentrated fiber sources -- even the cereal-sourced ones -- are very high in cellulose, but some cellulosic fibers come from non-food plant sources. Many of us are familiar with the "sawdust" accusations levied against early high-fiber breads but, chemically, cellulose is cellulose, no matter what the source. Typically these fibers start with pulp, which is bleached and purified to yield concentrated, white cellulose. This is then dried and reduced to the desired fiber length.

Gums. These tend to be expensive to use merely for fiber enrichment, so they are mainly used for their functional benefits. Because of their water solubility, they are useful in adding dietary fiber to beverages. Typically, even in this application, usage levels become self-limiting because gums often build significant viscosity. Modification can greatly reduce this viscosity. Partially hydrolyzed guar gum is a good example of a modified gum that can be used successfully in a large variety of applications.

Fruits and vegetables. As with the grain-sourced fibers, these fibers may be extracted from the outer skin, the flesh, or both. They, too, differ in composition depending on the source and how they are processed. Citrus fiber combines cellulosic and pectin-like materials. The proportions of these components vary depending on how the pulp, skin and albedo are isolated. Another fruit fiber, derived from apple flesh, has an insoluble-to-soluble fiber ratio of about 37 to 6. If the skin were included, the ratio would be much higher. Apple fiber contains an average of 43% total dietary fiber, but this amount varies by the season and can range as high as 60%. Blending different lots controls consistency and specific content.

Functionally speaking

  "The current emphasis for fiber use is function, rather than fortification. Often, the level of fiber used for function is not high enough for fulfilling fiber claims," says Jit Ang, director of technical services for Fiber Sales & Development Corp., St. Louis.

  A number of functional fibers provide a wide range of benefits. Non-digestible fiber has been used extensively as a bulking agent for fat and calorie reduction. Using fiber for these applications has been comprehensively covered by Food Product Design in the June 1996 issue, "Bulking Agents: Bulking Up While Scaling Down"; and the September 1996 cover story, "Designing Low-Calorie Foods." Obviously, the fewer calories a fiber has, the more effectively it can reduce calories in the finished product. Currently, only insoluble fiber is considered non-digestible by the FDA.

  Powdered cellulose is the standard anti-caking agent that has been used for many years to prevent caking and clumping of shredded and grated cheeses. It improves the flowability of dry mixes, thereby boosting the performance of packaging equipment and increasing efficiency. Apple fiber, now promoted for the same purpose, may offer label advantages.

  Many grain- and seed-sourced fibers provide flavor, texture and visual interest. For example, flaxseed adds a pleasant nutty flavor and a delicate crunch. The reddish-brown, oval seeds add visual interest. They typically contain 22% fiber, both soluble and insoluble, and 45% fat. This fat is of special interest because flax is the best known source for two essential fatty acids: linoleic and linolenic. Alpha-linolenic acids make up about 57% of the flaxseed fat. Studies have shown that these fatty acids may help reduce the risk of heart disease by preventing blood-clot formation.

  Milled flaxseed can be substituted for shortening or cooking oils at a 3:1 ratio in baked goods. Those who have substituted flax for shortening in this application have noted that products brown more rapidly. Studies by The Flax Council of Canada show improved loaf volume, oven spring, keeping quality, and significantly improved eating characteristics with the use of flax in baked goods. This is attributed to the soluble fiber portion of the flaxseed, flaxseed gum, whose properties resemble those of gum arabic.

  The optimum use level in most baked goods is approximately 8% of the total weight of dry ingredients or 15% on a flour basis. Because of flax's water-binding properties, formula water should be increased by 75% of the weight of the flax flour added. Increasing the yeast level by about 25% maintains the same proof time, texture and consistency.

  Sugar beet fiber also improves baked goods. Made from the cell walls of the sugar beet, this ingredient holds three to four times its weight in water during baking, freezing and thawing. Bread that contains beet fiber reportedly is richer tasting, and stays fresh and free from crumbling about two days longer than bread without the fiber. Adding 2% to 3% calculated on the flour weight is recommended for functional use. For fiber enrichment, higher levels may be used, depending on the character of the bread. Increasing the formula water by 3.5 times the weight of the beet fiber or reducing the quantity of flour by about six times the fiber weight is also recommended. In addition, the coarser particles of sugar beet fiber may be used as crust decorations.

  A sugar beet fiber called Fibrex®, imported from Sweden by Purity Foods Inc., Okemos, MI, contains approximately 73% dietary fiber, about a third of that being soluble. It is a high source of dietary protein (11%) and contains no gluten, as it is not sourced from grain. It contains no phytic acid or starch. It contains only 0.3% fat, and its residual sugar is less than 5%.

  Pectin is the source of the beet's soluble fiber, and this greatly influences its moisture-holding abilities. Finer grinds provide a slick mouthfeel, which makes the ingredient useful as a fat mimetic. This also makes it an excellent bulking agent for soups, sauces, fillings, gravies, and the like.

  "Because of the way the pectin is stored in the cell walls, the beet fiber yields less of a gum effect than straight pectin," says Fred Mesler, director, industrial ingredients division, Purity Foods. "This can be used to advantage by enhancing mouthfeel, when used for its thermo-stable capacity in meat and meatless patties." He also notes synergistic effects with the hulless, waxy variety of barley when beet fiber is used for fat replacement.  Pectins and gums build viscosity in solution. This can be a functional advantage if a thickener is required, but it limits the amount that can be added. Hydrolyzing guar gum greatly reduces its viscosity-building character, while only reducing its total dietary fiber content from 90% to 80%. Hydrolyzed guar gum is a cold-water soluble powder that is stable to heat, acid, salt and digestive enzymes. This flavorless and colorless product can extend cereal bowl life, absorb oil and water, replace fat, thicken, bind, aid extrusion, prevent starch dispersion, control ice crystallization, and function as an anti-caking, bulking and coating agent.

  Powdered cellulose acts as a noncaloric bulking agent, binder, thickener, anti-caking and anti-sticking agent, opacifier, cryostabilizer, texturizing agent, and carrier. It functions as an extrusion aid, improves cling, reduces fat pick--up in fried foods, and improves bake volume.

  The modified wheat-based fiber UltraCel, from Watson Foods, is another versatile fiber. It is composed primarily of insoluble fiber. This fiber usually remains unaffected by dispersed fat and protein solids, and soluble components such as minerals, sugars and short--chain oligiosaccharides.

  It can thicken low-viscosity products, such as fruit- and protein-based drinks and nutraceutical beverages, and can provide viscosity for soups and cultured dairy products. Because of its excellent water retention, it acts as a suspending and stabilizing agent. It works synergistically with xanthan gum, carboxymethylcellulose (CMC) and galactomannans, and it has a typically additive effect with other hydrocolloid stabilizers and viscosifiers. Because it absorbs moisture, it acts as a fat replacer in meats, icings and spreads, and as a moisture controller in condiments and coatings and can help add water to high-solids systems like doughs, spreads and meats.

  These fibers represent only a cross section of each of the categories of fibers available. They are cross-functional, and often provide unique attributes of their own. When choosing fiber ingredients, using several sources of fiber -creating functional complementing - is often the best option.

Why they work

  The multitude of functions fibers can provide makes them seem like miracle ingredients. Much of their functionality comes from their ability to absorb and, in some cases, to bind water at two to 10 times their weight. Water can serve as an economical and noncaloric addition to many products, and in its bound form it may increase product shelf life. Some fibers, such as powdered cellulose, contribute no calories, and others provide minimal amounts, making them excellent choices to provide solids and bulking for fat- and calorie-reduction.

  Binding water increases viscosity, which may be a blessing or bane. Increasing viscosity in sauces, dressings, dips and gravies may be the desired end in itself. For items such as barbecue sauce, fiber can increase the "cling," helping to keep them on foods.

  However, increasing the viscosity of some foods and beverages causes undesirable textural attributes and difficulty in processing. The water-binding character of fibers often makes them difficult to incorporate into food products, as they are strong competitors for the other ingredients that require water. Many new fiber ingredients are easier to use because their water absorption properties have been altered to limit or more evenly control absorption and, as in the case of hydrolyzed guar, reduce viscosity-forming properties.

  Gums and starches also build viscosity, but high levels may leave an undesirable gummy or starchy mouthfeel. Using powdered cellulose or another fiber to build part of the viscosity can reduce this effect.

  Water-holding ability can increase shelf life, as dryness often signals staleness in baked products. In other products, free water from syneresis or protein denaturation may be viewed by the consumer as a sensory defect or a sign of aging. Binding this water improves product quality and helps reduce the microbiological growth that is promoted by free water.

  Fibers also can control the water migration in frozen products that is promoted by freezing and thawing cycles. Fibers that hydrate very quickly, such as powdered cellulose, may be used in microwave entrees and mixes to promote even cooking. Their addition allows more uniform moisture distribution throughout the product and reduces uneven cooking during microwaving.

  In some products, water creates problems. Here, fibers may be used as anti-caking and anti-sticking agents. Besides preventing grated cheeses from clumping and caking, fibers improve the flowability and reduce caking of dry products like seasoning blends, soup and other dry mixes. In some cases the fiber absorbs oil rather than water to keep a product from caking.

  During extrusion, fiber may be used as an anti-sticking aid. Dough that sticks less to the extruder walls and screw element extrudes faster and requires less energy. Some research suggests that cellulose fibers may form complexes with starch granules in the presence of moisture, enhancing water binding.

  Certain fibers form extensive networks within and on the surface of food products. These provide structure before, during and after processing, and may reduce shrinkage in canned products and baked goods. Similarly, they can act as pseudo-emulsifiers in batter systems. Improving the aeration process results in better air cell retention and volume can be greatly increased in cakes and muffins.

  Adding fiber can alter texture -- sometimes to advantage, sometimes not. It can help a product retain its integrity during processing or give integrity to engineered foods. It can give body to fruit and vegetable sauces and pastes or give integrity to products such as reformed meats, shellfish analogs, products that contain cream cheese, and frozen novelties.

  The size and shape of the fiber particle often influences its functionality. With cellulose, the length of the fiber greatly influences texture, and a variety of unique textural properties can be derived by selecting different lengths or by blending them. Some ingredients add an undesirable gritty or dry texture to products, so one focus is to reduce the particle size of fibers in order to make them undetectable in products.

  Using low levels of some fibers, including cellulose and some gums, in fried food reduces fat pick-up during frying. This may be an effect of hydrophilic properties and molecular structure which permits the formation of significant amounts of additional hydrogen bonds. These bonds require more energy to displace during the frying process.

  Zallie expects future work on fibers to reduce any adverse organoleptic effects or offer processing advantages -- especially towards developing products with lower water-holding capacity and smaller particle size. He says, "Novelose is the first of what we hope to be a generation of resistant starches. We see resistant starch as a new category for both short- and long-term marketing opportunities as a functional fiber, functional food ingredient regardless of fiber content, and as a nutraceutical -- three distinct opportunities."

Function plus fortification

  Even though the primary interest in fiber may be function, it pays to take advantage of any nutritional benefits, too. The FDA Daily Recommended Value (DRV) for fiber is 25 grams per day. Formulation requirements are based on standardized serving sizes. Products to be labeled "Good Source" or "Fiber Fortified" must contain 2.5 grams per serving, or 10% of the DRV. Products labeled "High Fiber" must contain a minimum of 5 grams per serving, or 20% of the DRV.

  When formulating for fiber fortification, Zallie says, "The final food product claims must be based on the final food fiber content, not the fiber amount entered into the formula." He recommends monitoring fiber content before and after processing because processing, especially extrusion, may depolymerize and solubilize the fibers thereby decreasing their analysis as fiber. If resistant starches are used and annealing occurs during processing, fiber content may actually increase. This occurs because resistant starch content is enhanced by a combination of heat, moisture and pressure.

  In addition to the total dietary fiber content, other factors help drive fiber selection: the viscosity the fiber will impart, the amount of water absorbed, the particle size, and the flavor imparted or masked. Another consideration is the amount of "work" (energy and type of mixing or blending) required to incorporate the fiber into the product. This has processing implications and may end up affecting product flavor and texture, as well. Fibers that compete strongly for water require more severe processing (increased mix time, shear, and/or heat) for good dispersion than those that absorb less moisture.

  Often, functional complementing provides the optimum product. Oat and wheat bran have positive consumer images, but are low in fiber content and have high water-holding capacities. Adding enough bran to meet labeling goals will significantly impact finished product flavor, color and texture. Supplementing a lower amount of bran with another source of fiber such as resistant starch, white wheat fiber, or hydrolyzed guar gum (modified for high fiber content and low water absorption) would bump up the fiber content, and reduce the overall impact on flavor, color and texture.

  Scientists have discovered that a mixture of soluble and insoluble fibers is necessary to keep the intestinal tract healthy -- another reason for functional complementing.

  National is conducting feeding studies and other scientific exploration to globally investigate the potential of resistant starch as a nutraceutical. According to Zallie, the company believes this is a new ingredient category because resistant starches analyze as insoluble and yet are metabolized much like soluble fiber -- they are partially fermented in the large intestine. Resistant starches may have benefits beyond traditional fibers for colonic health and in diabetes management.

  Clinical research studies have shown that soluble fiber slows digestion and reduces the rate of glucose absorption (increasing glucose tolerance in diabetics), and has a positive effect on cholesterol, gall bladder contraction, bacterial translocation, and diarrhea. Insoluble fiber has been shown to be beneficial in regulating bowel movement and has been linked to reduced risks of certain types of cancer, including colon cancer.

  The FDA has proposed a rule that would allow claims that link oat bran and oatmeal with reduced risks of coronary heart disease. This would simplify the currently permitted health claims and make them easier to promote. The proposed rule is in response to a petition submitted by Quaker Oats Co. asking the agency to review health benefits of dietary fiber, specifically oat bran and oat meal. A Quaker spokesperson expects a response from the FDA sometime this fall.

  According to Zallie, "The fiber scientific community is working well within industry groups for the science that's evolving, developing analytical tools and methods. Several organizations and committees such as the International Life Sciences Institute (ILSI) and the American Association of Cereal Chemists (AACC) are reviewing, interpreting, and in some cases, helping to guide the scientific exploration by sponsoring conferences and forums where recent research results are discussed." Zallie believes that as the science evolves in fiber research, and various health benefits can be attributed to different fiber types, the FDA will expand health claim opportunities on a case-by-case basis.

  Until decisive nutritional evidence for claims of fiber's nutraceutical properties becomes available, food product designers might do well to leverage its worth as a functional ingredient and let the science catch up. Best of all, a product designer can use fiber purely for its functional value and feel good about providing nutritional value, too.

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