A resistant starch is any starch that resists enzymes during digestion. It’s also resistant to “cooking out,” and tends to form crystal structures that are resistant to digestion. Resistant starch in the diet, in specific amounts, may assist humans in resisting the accumulation of fat.
Starch molecules occur in two forms: amylose, a linear polymer composed of at least 200 (and up to several thousand) glucose molecules linked end-to-end; and amylopectin, a much larger, highly branched polymer containing up to hundreds of thousands of molecules of glucose linked in ways that form numerous short- and long-chain branches.
The ratio of amylose to amylopectin, as well as the molecular size of the molecules, varies widely in different crops, such as corn, wheat, rice and beans. Granules of common cornstarch are composed of approximately 75 percent amylopectin and 25 per cent amylose.
Amylose molecules have a natural tendency to form double-helix configurations, which aggregate into tightly packed, highly stable crystallites (by a process known as retrogradation). The terminal branches of amylopectin can also form short helices, but the resulting crystallites are much less stable and are easily disrupted. From resistant starch to fiber is a matter of degree, but it is now apparent these compounds have important roles in digestion.
Resistant starch and digestion
Since research in the mid-1980s, the definition of resistant starch has grown and changed. Studies in 1988 by Kay Behall of USDA on the effect of high-amylase starch on healthy subjects showed definite changes in the way the starch was digested, and the data suggested high amylose starch reduced the accumulation of triglycerides in blood. Results also suggested differences in insulin action when subjects consumed muffins, cornflakes and other foods that included a large proportion of high-amylose cornstarch.
National Starch introduced Hi-maize resistant starches in 2002 and flour and meal from Hi-maize high-amylose corn earlier this year.
As the crystalline structure of starches became better understood, the characteristic of certain fractions of high-amylose starch was redefined as “resistant.” Such starch could come from high-amylose grain or other starches that had been either chemically treated or cooked and allowed to retrograde (crystallize). Since then, four types of resistant starch have been defined:
- RS1 (resistant starch that is physically encased by whole grains)
- RS2 (a granular resistant starch)
- RS3 (nongranular, retrograded or crystalline resistant starch)
- RS4 (a manufactured resistant starch)
This makes resistant starch somewhat of a moving target. How foods are prepared, how starches are processed and how they relate to fiber is important. For instance, a cold, boiled potato contains about 13.5 percent resistant starch of the RS 3 type, while the same boiled potato served hot contains about 6.7 percent resistant RS3 starch. Whole-meal bread may contain 1.6 percent RS3, and lentils (cooked and cooled) contain 16.4 percent resistant starch in combined RS1 and RS3 types.
In late 2004, the journal <I>Nutrition and Metabolism</I> reported that consuming 5.4 percent of total carbohydrate as resistant starch resulted in increased metabolism of fat (http://www.nutritionandmetabolism.com/content/1/1/8). The report was by Janine Higgins of the University of Colorado Health Sciences Center, Center for Human Nutrition (Denver) and a team including researchers from the University of Vermont (Burlington), University of Wollongong (Australia) and the Dept. of Preventive and Social Medicine at the University of Otago (New Zealand).
“Our research has shown that, just by eating a meal containing resistant starch, you can burn 20 to 25 percent more fat, and this increase is sustained throughout the day – even if only one meal contains resistant starch,” Higgins commented. “Also, (the) effect is sustained if you keep eating resistant starch on a daily basis.”
Such discoveries about resistant starch fit with consumer interest in avoiding obesity, diabetes, heart disease and other maladies. According to Higgins, the reason resistant starch works is due to an anomaly in the way digestion proceeds. “The resistant starch actually changes the order in which the body burns food,” she explains. “Usually carbohydrates are used first, but resistant starch seems to move fat to the top of the list to be burned for energy before it has a chance to be stored.”
Note to Marketing
|Exactly how marketers can claim the effects of resistant starch on a label is a tough question. In the U.S., resistant starch, unless it tests as fiber, is labeled as corn starch or modified food starch. If a firm decides to make a reduced-calorie label claim, it’s wise to discuss it either with the company’s legal staff or FDA.|
A major problem with the development of fiber and resistant starch as ingredients that can be labeled on foods is the difficulty of determining how much resistant starch is present in a food. In 2002, the American Organization of Analytical Chemists (AOAC) published a method for determining the amount of resistant starch. Different tests are used to quantify fiber. Unless the carbohydrate tests for fiber, it is labeled as starch, which is less descriptive of its actual role in digestion. While there is still some controversy about the method, it is being used.
Legumes = resistant starch + fiber
The similarity of resistant starch and fiber is described in the February issue of the Journal of Nutrition, by the University of Illinois, Urbana, research team headed by George Fahey Jr. Fahey, et. al. report legumes contain substantially higher percentages of resistant starch than do cereal grains, flours and grain-based food products. Resistant starch was equated to dietary fiber in that both bypass digestion in the stomach and small intestine before settling in the colon. Bacteria present in the human gut attack resistant starch as they do dietary fiber, producing butyrate.
Butyrate is a short-chained fatty acid which has shown cancer-preventing qualities. The Illinois study provides the first database of the percentages of starch and fiber in common food and feed ingredients. The researchers also determined how and where in vitro digestion occurred by studying digestion in the lower part of the small intestine in a dog model representative of the human digestive tract.
"The nice thing about legumes is they have a great deal of dietary fiber plus the resistant starch," said Fahey. "With their protein, fiber and resistant starch, legumes offer good nutrition. Until now, we never knew legumes had so much of their starch in the form of resistant starch."
Of the 29 food and feed ingredients studied, the legumes (seven varieties) contained substantially higher percentages of both dietary fiber and resistant starch. Black beans, for instance, contain the highest amount of total dietary fiber (43 percent), and 63 percent of their total starch content is resistant starch. Frozen green peas, when cooked, contain about 26.3 per cent resistant starch as RS1 and RS3.
Resistant starch sourcing options
MGP Ingredients Inc. (www.mgpingredients.com), Atchison, Kan., for some time has been producing resistant starches made from wheat and potatoes. Its Fibersym family of products feature low water-holding capacity and total dietary fiber ranging from 70-80 percent. Because they are derived from wheat and potatoes, they possess a neutral flavor, white color and smooth texture, and as a result can be incorporated into a wide range of foods, such as bread, tortillas, muffins, waffles, breakfast cereals, cookies, nutritional bars and snack foods.
MGP also has a business alliance with Cargill Inc. (www.cargill.com), Minneapolis, for the production and marketing of a resistant starch product called Fibersym HA. The product is derived from high-amylose corn and is suitable for use in a variety of lower-net-carbohydrate food products.
Cargill offered booth visitors a “high-fiber bun” at June’s IFT show that included ActiStar resistant starch … as well as a white whole-wheat flour, inulin and high-oleic sunflower oil.
Cargill’s European division Cerestar (www.cerestar.com), Mechelen, Belgium, introduced a tapioca-based resistant starch, ActiStar RT, in 2005. ActiStar RT is said to provide the benefits of high fiber in lower net-carbohydrate food formulations. Originally developed with an eye toward the low-carb market, the material is manufactured under an exclusive license granted by MGP. It is made by enzymatically debranching a tapioca maltodextrin and then causing retrogradation so the granules lose their crystalline structure, then aging the solution with cooling to form partially crystalline material that is not attacked by normal stomach enzymes.
ActiStar RT has low water-holding capacity, permitting high levels of inclusion with few formulation changes and a non-gummy texture. Since tapioca, the source of resistant starch in ActiStar RT, is the blandest of all starches it doesn’t detract from the desired taste, texture, or appearance of finished products. It is recommended for use in bread, cereal bars, biscuits, cookies and muesli. In beverages, low-fat fermented milks and ultra-pasteurized flavored-milk drinks can be successful vehicles for the product. Since ActiStar RT is a very fine particle, it blends easily with other ingredients and causes no grittiness. This makes it highly suitable for ready-to-use powdered mixes such as instant soups and chocolate drink mixes.
Sugar beets have been a source of fiber that behaves much like resistant starch but tests as fiber. Danisco A/S (www.danisco.com), Ardsley, N.Y., has recommended the use of its Fibrex sugar beet-based product as a fat replacer in meat products. Because much of the fiber is pectin, it produces a thick gel that behaves like fat in certain products. The sugar beet fiber is all natural, non-GMO, GRAS, USDA-approved in meats and poultry and HPB approved in Canada, and it can be obtained in an organic version.
Another fiber product line is the range of oligofructose and inulin products, made from chicory root or rice, produced by Orafti (www.orafti.com), Malvern, Pa. One of the company’s newer products, Beneo HP, is a partially hydrolyzed inulin dietary fiber that can be used to replace gelatin. Many of Orafti’s products are also available as organic products.
Corn resistant starch tests as fiber
National Starch Food Innovation (www.foodinnovation.com), Bridgewater, N.J., introduced Hi-maize resistant starches in 2002, although flour and meal from Hi-maize high-amylose corn were just introduced in March of this year. The products contain about 25 percent fiber, as tested by AOAC (Method 991.43 or 985.29 for insoluble fiber).
“Adding nutritional corn flours and corn meals to the Hi-Maize portfolio brings more options to food formulators who want to provide more nutritious, natural and wholesome convenience food products to consumers,” said Mike Klacik, senior director of nutrition for National Starch. “This is good news for consumers seeking to increase their daily fiber consumption in their favorite extruded or baked foods.”
Both the starches and the flour and meal can be used in a wide variety of foods, including breads, pasta or ready-to-eat breakfast cereals without changing the flavor of texture of foods.
Path of most resistance
|National Starch Food Innovation (www.foodinnovation.com), Bridgewater, N.J., the folks who helped put resistant starch on the map, are now putting it on the World Wide Web. The company's web site www.resistantstarch.com is specifically designed to help nutrition professionals catch up and stay up-to-date on this remarkably healthy fiber. Anything you ever needed or wanted to know about resistant starch is now at your fingertips 24/7.|
“Dieters like the benefits of fiber. ‘Whole grain’ alone doesn’t provide all of the benefits of fiber,” says Rhonda Witwer, National Starch’s manager of nutrition. Witwer expresses concern about the recent interest in glycemic index, preferring the phrase “glycemic load” or “glycemic response” of foods. (See “Glycemic Index: use with caution” and “G.I. Blues” at www.foodprocessing.com.)
Glycemic index alone doesn’t encourage fiber consumption, which offers the most (weight management) advantage. The 2005 Dietary Guidelines for Americans recommend consuming 14g of fiber per 1,000 calories consumed. A typical adult male consuming 2,500 calories would require 35g of fiber daily, while a typical adult female consuming 2,000 calories would require 28g of fiber daily.
The entire daily recommended intake of dietary fiber could be consumed from Hi-maize without negative digestive side effects associated with other forms of fiber. Use of those amounts of fiber as resistant starch from Hi-maize flour or meal can be accommodated in a wide variety of foods, including bread, cereals and pastas.
Nearly 800 studies are published concerning resistant starches and various disease states, such as diabetes, cardiovascular conditions, metabolic syndrome and cancer. As these carbohydrate products are better understood, and as their role in digestion is elucidated, the multipurpose nature of these ingredients will be clearer.
The difference between resistant starch and fiber is currently partly a regulatory issue. More and more studies indicate both are helpful in metabolism and in affecting fat digestion, as well as reducing some aspects of diabetes.