Fiber is a soughtafter
for consumers and
alike, but all fibers
are not created
Consumers today know fiber provides health benefits and are making it a priority to select high fiber products, as manufacturers meet the demand by flooding supermarket shelves with fiber-added options.
According to a report from the USDA focused on a 10-year period from 1995/1996 to 2005/2006, consumer use of nutrition labels overall declined, while consumer use of fiber information on labels increased two percent.
“The beta glucan (soluble fiber) claims around oat-based products approved by the FDA in the mid-1990s opened the door to marketing health claims,” says Bill Bonner, senior vice president, research and development, technical sales, 21st Century Grain Processing, Kansas City, Mo. Ingredients have evolved to support flavorful products that support these health claims.
Yet despite consumer awareness and increased media attention on the importance of fiber, and hundreds of high-fiber products on the market, Americans still are not consuming fiber in large enough quantities.
“Statistically, Americans only get half the fiber required, 15 g per day, while the recommendation is 25 g to 35 g per day,” says Riska Platt, MS, RD, spokesperson, The American Heart Association (AHA), New York. AHA gives a fiber recommendation according to calories: 14 g of fiber for every 1,000 calories consumed, which equals about 28 g on a 2,000-calorie diet.
While consumers know fiber is good for them, many do not realize all fibers are not created equal. Many different kinds of fiber exist and not only offer different health benefits, but also function in diverse ways.
Soluble fiber tends to build viscosity in the small intestine, while insoluble fiber provides a bulking effect. Soluble fiber has been associated with decreased risk of cardiovascular disease and reduction in LDL (bad) cholesterol. “Soluble fiber is believed to actually lower cholesterol by binding some of the cholesterol and bile acids in the intestinal track, causing them to be excreted instead of absorbed,” Platt says. Oats offer the highest amount of soluble fiber, but rice bran, barley, peas, apple pulp, beans and oat bran also contain high amounts.
Insoluble fiber balances acidity levels in the intestines, and moves bulk, promoting regularity. It may also decrease inflammation, which is an underlying factor in cardiovascular disease, diabetes and obesity.
“With soluble fibers, people tend to think more of health claims, but insoluble fibers are great for laxation and bulking of the stool and that is an important health aspect,” says Jit Ang, executive vice president, R&D, International Fiber Corp., Buffalo, N.Y. Insoluble fibers also increase satiety and, because insoluble fibers contain zero calories, they help reduce the caloric content of baked products. Bamboo, cottonseed and sugar cane fiber, barley, rice, rye, wheat and cellulose are all examples of insoluble fibers.
The best fiber for bakers depends on marketing and economics, Ang says. One bakery might want natural or organic on the label, while another might want the most economical choice. Cellulose, he says, is abundant and a less expensive raw material, and therefore, an economical choice.
In any kind of chemically leavened products, such as cakes or muffins, adding certain forms of insoluble fibers can provide better texture, volume and can improve the yield. In addition, insoluble fibers bind moisture and can prolong shelf life. In certain types of microwaveable products, insoluble fiber helps achieve better heating properties. “Fibers absorb more moisture than flour or other components used in bakery products,” Ang says. Therefore, bakers may need to adjust the moisture content of the batter or dough to make it compatible with machines.
When making high-fiber bread, high levels of fiber also can dilute the gluten content in the flour. Therefore, to make good bread and also have ideal fermentation and mixing, bakers need to replace some of the lost protein or gluten by using vital wheat gluten to avoid a weak dough, Ang says. Because the water absorption is different in high-fiber doughs, typically, more water is needed to get proper mixing and development. Plus, the mixing time may be longer.
Formulating with soluble fibers will differ depending on the type used. “There are two kinds: soluble that are completely soluble and have little, if any, effect on viscosity, such as inulin and polydextrose, and soluble fibers with a significant thickening effect, such as gums. If you're using soluble fibers with a thickening effect, you can't add too much or your batter becomes a dough. But if you're using soluble fibers without viscosifying effects, you can add more without having problems with the rheology,” Ang adds.
In addition, bakers interested in formulating with barley beta glucan (BBG), may find it easier to formulate with a BBG with reduced molecular weight, which lowers LDL cholesterol, but has no viscosity effect, says Joseph Keenan, M.D., professor, University of Minnesota School of Food Science and Nutrition, St. Paul.
Tate & Lyle's soluble corn fiber is stable in low pH, which is important in bakery fillings. “You don't want to lose fiber when you add it in an acidic system, and some soluble fibers are not stable below pH 4.5,” says Doris Dougherty, senior food scientist, Tate & Lyle, Decatur, Ill.
When testing formulations with higher fiber, initial prototypes may turn out too hard. This problem often is solved by adjusting the protein, fat and/or emulsifier, Ang says.
Because high fiber doughs typically contain more water, these may take longer to bake. Sometimes, in an effort to get the baking done in the same amount of time, a baker will raise the temperature, which might create a hard crust. Or, they might overbake to achieve proper doneness, which might also create a hard crust and dark crust color. A good formulator can help modify the formula to avoid an unappealing consistency during development and baking, Ang says.
Resistant starches currently are being hailed as prebiotic fibers. The biggest difference between natural resistant starch and other dietary fiber is natural resistant starch's fermentation in the large intestine has been shown to have metabolic benefits beyond that shown by prebiotic fibers.
“Resistant starches are beneficial in supporting healthy colon flora and discouraging pathological flora. The fermentation by-products (short-chained fatty acids, especially butyrate) are essential for colon nutrition,” Keenan says.
Studies have shown natural resistant starches increase insulin sensitivity and help the body burn more fat, and several animal studies show the fermentation turns on genes in the large intestines that make the important satiety hormones GLP-1 and PYY, says Rhonda Witwer, senior business development manager, nutrition, National Starch Food Innovation, Bridgewater, N.J. By eating one meal containing resistant starch, healthy people burned 20 percent to 25 percent more fat during the day. “These are not generic fiber benefits, but benefits specific to the fermentation of resistant starch.”
Non-fermentable fibers and minimally fermentable fibers, such as cellulose, psyllium and wheat bran do not offer the same benefits, Witwer says. While certain soluble fibers, such as inulin and FOS, are fermented, their dose tolerance prevents them from being used at levels where they might achieve these benefits.
Resistant starches also are not created equal. Four kinds of resistant starch are available: RS1 consists of unprocessed whole grains where the starch is protected by a barrier, such as a seed coat; RS2 occurs in its natural granular form, such as in uncooked potatoes, green bananas and high amylose corn; RS3 forms when starch-containing foods are cooked and cooled, such as in bread, and baked-and-cooled potatoes or retrograded high amylose corn; RS4 is starch that has been chemically modified to resist digestion. Different resistant starches digest differently in the small intestine and ferment differently in the large intestine, and studies are still deciding the benefits of each.
Like prebiotic fibers, natural resistant starches encourage the growth of good bacteria and reduce harmful bacteria and compounds, such as ammonia and phenols. But are resistant starches actually prebiotic fibers? It is not clear, as clinical studies have shown natural resistant starch is consumed by a wide variety of bacteria.
To be prebiotic, a fiber must be preferrentially consumed by the “beneficial bugs” (primarily, bifidobacteria and lactobacillus), which increase intestinal health, Witwer notes. While Type RS2 resistant starch has been shown to increase many biomarkers of intestinal health, human studies have not confirmed this. It does not meet the technical definition of a “prebiotic” fiber.
Animal studies have shown National Starch's RS2 resistant starch increases bifidobacteria and lactobacillus, but only the bifido consumes resistant starch directly. In addition, resistant starch also is consumed by what had been previously assumed to be “bad bugs,” such as certain strains of clostridium, but with a positive result: it produces butyrate needed for a healthy colon, turns on the genes that make GLP-1 and PYY (satiety hormones) and improves insulin sensitivity.
Broadening the definition of prebiotic to include fibers that promote health through fermentation, regardless of the type of bacteria that consumes it, is being discussed, Witwer says. “If that is adopted, then absolutely we are a prebiotic fiber. We have all these benefits, and we know those two bacteria are involved, but it is not limited to those two strains.”
Tate & Lyle conducted clinical studies to show prebiotic effects from its RS3 resistant starch, which also lowers glycemic response and offers 1.7 calories per gram. In addition, it is thermally stable, which can be beneficial in products with severe processing requirements, such as extrusion. Low water holding also is a consideration, as in a cookie application where maintaining shape is important. “If a cookie takes on water, the cookie height will increase and the spread will decrease. To maintain cookie shape, you want low water holding even during baking to maintain the shelf life expected of a crisp cookie,” Dougherty notes.
Experts agree fibers function differently and blending different fibers together can allow bakers to get higher fiber claims on products. “Oat fiber or wheat bran may hold more water than resistant starch, so blending them is an economical choice. Tate & Lyle's RS3 resistant starch is low in water holding, so it allows bakers to combine other fibers with it that might hold more water,” Dougherty says.
Natural Starch's RS2 resistant starch replaces up to 20 percent of the flour in baked products. Its water holding capacity is slightly higher than flour and lower than other types of fiber. Minor adjustments in water and gluten would be required depending on the formulation.
Tate & Lyle's soluble corn fiber functions as a corn syrup that also adds fiber and can be used in combination with resistant starch to achieve high fiber levels without affecting product quality, Dougherty adds.
Because all fibers offer different health and functional benefits, a blend of fibers often achieves the best product.