Food Product Design: Ingredient Insight - September 2005 - A Starch That's Hard to Resist

September 2005

A Starch That's Hard to Resist

By Lynn A. KuntzContributing Editor

For many years, starch was known for its valuable role as a stabilizer in foods and beverages, but in nutritional circles, was not highly regarded. That view is changing with the discovery of a type of starch known as resistant starch (RS).

Counting to four Researchers have defined four types of RS based on their source, derivation and physical characteristics. RS1 is physically trapped within food -- amylolytic enzymes in the digestive tract have no effect on it because the enzymes can't physically reach them to break them down. A second type, called RS2, remains unaffected by enzymes until it gelatinizes. This ungelatinized, granular starch occurs naturally in some fruits and vegetables, such bananas, peas and uncooked potatoes, and can be derived from high-amylose starch using a physical process. RS3 starch, a nongranular type, is retrograded, giving it a crystalline structure, and forms in starchy, heat-processed products, like bread and breakfast cereals. RS4 can be manufactured from starches from various sources, including corn, wheat, tapioca and potato, using chemical modification. This last type tends to have the highest fiber levels.

"The chemical modification allows you to work with several base starches, versus just the high-amylose products," notes Dorothy Peterson, product line specialist, starch and starch derivatives, Cargill, Inc., Minneapolis. "It can be applied to basically any type of starch." She notes that RS4 products should be labeled "modified food starch."

National Starch Food Innovation, Bridgewater, NJ introduced some of the first RS ingredients on the market, according to Rhonda Witwer, business development manager of nutrition. "Hi-maize is labeled as cornstarch within the U.S. market. Novelose is labeled as maltodextrin, as it is an RS3," she says.

Kansas State University, Manhattan grain-science researchers discovered a method to modify starches to create resistant starch. The K-State Research Foundation patented this technology. In March 2003, the Foundation licensed the technology exclusively to MGP Ingredients, Inc. (MGPI), Atchison, KS. The patent covers a special modification of any starch derived from the cereal grains, roots, tubers and legumes; for example, from wheat, corn, oats, rice, potato, tapioca and mung beans. Using this patent, MGPI manufactures Fibersym(TM) 70, a wheat-based RS that contains 70% total dietary fiber, and Fibersym 80ST, a potato-based type that contains 80% total dietary fiber (AOAC Method 991.43).

"Fibersym 70, a wheat-based resistant starch, has very low water-holding properties and is ideal for wheat-based foods," explains Steve Ham, director of marketing, specialty ingredients, MGPI. "Fibersym 80ST, derived from potatoes, has slightly higher water-holding properties, which can impact finished food products, such as cookie spread or volume of a muffin."

MGPI and Cargill formed a business alliance for the production and marketing of a resistant-starch product called Fibersym(TM) HA, derived from high-amylose corn. Currently, Cargill offers tapioca-based RS4, ActiStar(TM) RT, which has a low water-holding capacity, permitting high levels in formulations without producing a gummy texture. "What really differentiates it is that it is the highest dietary fiber resistant starch on the market at about 85% total dietary fiber," says Peterson. "Since tapioca has such a bland flavor profile, we're able to take advantage of that in ActiStar(TM) RT -- it doesn't have that typical corn flavor."

Functionally fiber RS1, RS2 and RS4 starches meet the definition of "dietary fiber." In the digestive system, these act like insoluble fibers, adding to fecal bulk and increasing butyrate production, which improves gastrointestinal health. Butyrate fermentation occurs in the large intestine and might prevent tumor growth. Increasing fecal bulk can help prevent constipation, diverticulosis and hemorrhoids, as well as dilute compounds that might cause cancer-cell formation.

Slow digestion of these starches results in a sustained, low elevation of blood sugar. By providing a low glycemic load to the blood, they might delay hunger and reduce incidence of type 2 diabetes. RS might also act as a prebiotic, increasing good bacteria in the large intestine while decreasing the bad bacteria.

"More than 180 research studies have been published on nutritional benefits of high-amylose-corn resistant starches over the past 15 years, many of which utilized Hi-maize itself," says Witwer. "Thus, a lot of the health benefits are being discovered through research utilizing Hi-maize. For instance, the Oxford Lipid Metabolism Group has published that dietary consumption of Hi-maize increases insulin sensitivity in healthy people. And the University of Colorado has published that dietary consumption of Hi-maize increases lipid oxidation within the body of healthy people and shifts the body from burning carbohydrates as its energy source to burning stored fat."

Peterson notes that, "resistant starches are insoluble fiber and they must remain that way and stay in the ungelatinized form to function in the products. One of the nice features, though, is that resistant starches are very well-tolerated. A lot of other fibers create issues in the gastrointestinal tract. So, you can put higher levels in products without any negative impact, making it easier to get to a 'good' or 'excellent' source of fiber."

Adding resistants isn't futile "Resistant starches are added to formulas to boost dietary-fiber content and reduce caloric content, so a use level typically coincides with achieving labeling claims for 'good source of fiber' -- 2.5 grams per serving -- or 'excellent source of fiber' -- 5.0 grams per serving," says Ham. Often, this is difficult to achieve with traditional fiber ingredients and formulate a consumer-acceptable finished product.

However, resistant starch provides an opportunity to add high fiber levels without significant changes to finished-product quality. For example, Ham notes that Fibersym resistant starches "possess a white color, smooth texture, neutral taste and very low water-holding properties for ease of incorporation with minimal formulation changes. Product applications include white pan breads, wheat breads, pizza crust, tortillas, pasta, bakery mixes and sweet goods."

RS starches' small particle size, bland flavor and white color, as well as their tendency to absorb less water than many other fibers, means they can be added into many baked products at significant fiber levels with less negative textural effects than other fibers. RS products have little to no swelling or ingredient interaction, so product designers can avoid some of the problems encountered with high levels of other fibers. For example, in bread, fibers with a high water-holding capacity can change the dough rheology, causing difficulties in molding, panning and slicing, and possibly requiring a longer bake time to reach the target moisture level. Some formulas might require additional gluten if the RS level is high, which in effect "dilutes" the flour's gluten.

Researchers at National Starch and the American Institute of Baking, Manhattan, KS, successfully fortified breads with an RS2 starch at levels up to 5 grams fiber per 50-gram serving (10% TDF), either alone or in combination with oat fiber. They also formulated high-fiber breads, crackers and muffins with RS2 starches. Compared to breads made with other fibers, they exhibited a brighter crumb and better mouthfeel, as well as better loaf volume. Crackers formulated with granular RS were rated as similar to the control and were crisper and not as hard as traditional-fiber crackers. Breakfast cereals show better expansion and texture, and possibly extended the bowl life. This RS also adds crispness to waffles and French toast and might reduce sogginess when these contact syrup.

"In most applications, Hi-maize is an easy replacement for flour on a 1:1 basis," say Witwer. "In the case of bread, some wheat gluten may be needed to replace the protein component that is lost from the flour, because the gluten is so critical to the proper texture of the bread formulation."

One trend is to use these RS ingredients in combination with other fibers "to improve either a process issue or a finished-product issue," says Peterson. "A good example is whole grains: While it's good to have the whole grains on the label -- the consumer has that recognition that they're healthy -- you may not be able to achieve the level of fiber you want on the label unless you supplement it with resistant starch."

One aspect product designers have to be aware of is that the process a food undergoes might change the RS into a digestible carbohydrate. "Resistant starches can be affected by processing conditions, as heat, shear and pH can reduce dietary-fiber levels," cautions Ham. "Analyzing dietary-fiber content through lab analysis is advisable over nutritional software to compensate for any dietary-fiber loss during processing."

The RS4s tend to have the best process tolerance. "Natural resistant starches are typically stable to baking conditions, but can be affected by high shear or extrusion conditions as you would find in cereal manufacturing," warns Witwer. "If the natural crystalline structure of the RS is damaged, it becomes rapidly digested starch and loses its resistance."

It's difficult to find ingredients that combine health benefits and desirable functionality. In light of that fact, resistant starch is good news for consumers and product designers alike.    

Suanne Klahorst is associate director of the California Institute of Food and Agricultural Research (CIFAR) at the University of California, Davis. CIFAR facilitates information exchange and research collaboration between the campus and extramural organizations in food, nutrition and human health. She can be contacted at [email protected].

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