Resistance is not futile (where starch is concerned)

Resistant starches are helping meet the low-carb craze, but their functionality should keep them around longer than the current diets.

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Pasta can be made with resistant starch,
reducing carbs to less than 6 g per serving.


By Frances Katz, Senior Technical Editor

They’re starches, but they don’t always act like starches, especially where digestibility is concerned. Resistant starches (RS) behave much like ordinary starch but, because they are not easily digested, they may be assigned zero calories in foods in some cases. And of special interest in the current dieting trend, they help foods carry a reduced carbohydrate label.

“RS is of increasing interest as a food ingredient. Unlike common dietary fiber sources, RS does not hold much water and, thus may be a preferred fiber source for use in low moisture products such as cookies and crackers,” Kansas State University researchers Paul Seib and Kyungsoo Woo wrote in a patent application, which was granted in 1999. “Also, RS is free of a gritty mouthfeel, and unlike traditional fiber sources does not significantly alter flavor and textural properties of foods. Those characteristics can improve the processing and quality of foods such as baked and extruded products when RS is added. Furthermore, RS is measured as dietary fiber, and may be assigned zero calories.”

NOTE TO PLANT OPS

Because water-holding capacity of resistant starches is usually lower than most other starches, moving foods around the plant -- whether mixing, pumping, or shaping products -- may require a little more power, especially if the food is a relatively low-moisture product.

Also, browning on surfaces is likely to be less apparent, so baking ovens for breads may need a different temperature setting. Higher solids cause heat penetration differences in canned foods. Don’t assume that changing a starch won’t change the processing parameters. But there may be plus sides, too: Changes in the water activity of the finished foods may permit a reduction in preservatives.

In other words, it can be considered fiber for labeling purposes, but acts more like starch for manufacturing purposes.

However, shearing, mixing, and heating may change the amount of starch that remains resistant to digestion. So it’s necessary to analyze the end-food products as they are ready for use by the consumer, notes a research director of a major food manufacturing company, which is evaluating the various available resistant starch products in different foods.

The company is careful about regulations, and diligent about the science that provides labeling back-up. Officials are concerned about the consumer’s perception that Big Food could confuse them by changing the message every few years.

“First we take out the fat and increase the carbohydrates, then we take out the carbohydrates and add protein, while the consumer gains more weight,” notes the scientist, who prefers to remain anonymous. “We have to make sure we have the science right, and our communication to the consumer needs to be clear and consistent. We’re developing a position on RS, but it’s too soon to say where and when we might use these ingredients. But they are unique, and may be very useful, especially if we find a way to communicate the value of the foods to the consumer.”

Twenty years of interest

Early mentions of resistant starch usually set the phrase off with quotation marks. The phrase started appearing sometime around 1982, with high levels of interest at the Flair-Flow Europe workshop on resistant starch in Crete in 1991, at which a number of papers were presented. These papers discussed the digestibility of RS, fermentation and the effect of this material on blood fats and bile acids in the colon, as well as testing methods. As a result, resistant starch was primarily a European subject of discussion for most of the 1980s.

But by the early 1990s, the U.S. Dept. of Agriculture was looking into resistant starch, and its major supply, high-amylose corn starch, was being studied by researcher Kay Behall. Behall fed healthy subjects food products made from high-amylose starches, including muffins, bread, and corn flakes. She found subjects who ate the high-amylose diet had changed insulin-producing patterns and lower serum cholesterol.

Research on the subject has been under way at the Beltsville Human Nutrition Research Center for some 27 years. This work includes the earliest and longest human study feeding high-amylose starch as the primary starch source, approximately half of the total carbohydrates in the diet.

Labeling issues have matched nutritional and functional issues in interest. The American Assn. of Cereal Chemists has launched an Ad Hoc Glycemic (Net) Carbohydrate Definition Committee to develop a science-based definition of glycemic carbohydrates. At the same time, National Starch has filed a citizen’s petition to modify carbohydrate content on food labels. National Starch wants fiber content to be listed independently and excluded from the “total carbohydrate” declaration on nutritional labels.

The designation for fiber, which includes National’s high-amylose products, should be outside the carbohydrate designation on the Nutrition Facts Panel to better correlate with label statements in Europe and the rest of the world, according to Rhonda Witwer, the development manager for nutrition at National Starch (www.resistantstarch.com). “These products test as fiber. Clinical studies clearly show the RS1, RS2 and RS3 types of resistant starches behave as fiber,” she says.

However, “Not all kinds of resistant starches react the same way, so the evidence supporting each type of resistant starch must be considered,” Witwer continues. “Separating fiber out of the total carbohydrate content will encourage increased fiber consumption. For good health, consumers should eat a lot of different kinds of fiber, and resistant starch is becoming recognized for its positive impact.”

Definitions of the starches and their functionalities were first considered around 1987. Three classes of dietary starch were proposed: RDS (rapidly digested starch, which is digested in the small intestine), SDS (slowly digested starch, which is slowly but completely digested in the small intestine and includes raw cereal starch and cooked pasta) and RS (resistant starch, which resists digestion in the small intestine but may be fermented in the large intestine).

Furthermore, there are four categories of RS, all based on the causes of resistance:

  • RS1, physically inaccessible starch due to entrapment of granules within a protein matrix or within a plant cell wall, such as in partially milled grain or legumes after cooking.
  • RS2, raw starch granules, such as those from potato or green banana, that resist digestion by alpha-amylase, possibly because those granules lack micropores through their surface.
  • RS3, retrograded amylose formed by heat/moisture treatment of starch or starch foods, such as occurs in cooked/cooled potato and corn flakes.
  • RS4, which includes chemically modified starches, such as acetylated, hydroxypropylated, or cross-linked starches that resist digestion by alpha-amylase.
Those modified starches would be detected by the in vitro assay of RS. Some RS4 starch may not be fermented in the colon.

RS is counted with the dietary fiber fraction of food and is believed to function as fiber in the human digestive tract. The reduced bioavailability of RS in the human gastrointestinal tract leads to slow glucose release, which reduces blood sugar and blood lipids, including cholesterol and triglycerides.

When RS reaches the colon, it is fermented to hydrogen, methane, carbon dioxide, lactic acid (transient) and short-chain fatty acids (acetate, propionate and butyrate), which may help reduce colon diseases. According to a white paper by Opta Food Ingredients, an early producer of resistant starch, RS assays as an insoluble fiber but behaves physiologically like a soluble fiber.

Bread made with resistant starches retains carbohydrate utility, but reduces carbs to 5 g or so per slice.

How they relate to starch structure

It has been understood that the structure of starch is related to resistant starch, or at least to the amount of resistant starch that can be derived from a starch source. Amylose, the linear fraction of starch, is resistant to the action of enzymes and digesting acids in the stomach and small intestine.

“Normal” starch can be treated to resemble amylose by reacting it with debranching enzymes. The debranching enzyme removes branches, leaving a linear structure that is not easily attacked by digestive enzymes. However, the granular structure of the starch is separate and distinct.

The rheology (texture) of starch solutions is different when the starch is cross-linked as a prevention to digestion, according to James BeMiller, director emeritus of the Whistler Carbohydrate Center of Purdue University. He notes different sources of resistant starch and fiber are included in the AOAC fiber analysis, but that total number didn’t provide good guidance to the consumer. “It’s what we have now, but it’s being studied avidly, and the whole net carb/total fiber puzzle will be solved in the near future.”

Just as there are four designations for resistant starch, there are also several sources for the product. The most common American source is high-amylose corn, a specialty grain grown by a few hundred farmers for one of the two corn wet millers that processes the product in the U.S. Common corn (referred to as No. 2 yellow) contains about 26 percent apparent amylose, the mostly linear polymer of glucose molecules. Through selective breeding of a mutant strain (designated ae, amylase-extender), corn can be produced with 50 to 70 percent amylose, and some strains can consist of 90 percent or more amylase.

Wheat and potatoes also are sources for resistant starch. These resistant starches are made by chemically modifying the starch so it resists digestion. In a patented system, the starches form phosphorylated distarch phosphodiester using a mixture of phosphates, which is not attacked by enzymes in the human digestive system. According to Seib at Kansas State, the chemically modified starches (made in accordance with FDA requirements for food starch modified) swell somewhat during processing, losing some of the resistant starch content. Assays should be done after the food is prepared in order to be accurate.

Market development

In the early 1980s, Opta Food Ingredients began to develop a resistant starch (RS3) by debranching high-amylose corn starch in several steps and allowing it to retrograde. The product, called CrystaLean, is used in diet bars, cookies and other lowfat products. The product is available today from SunOpta Inc. (www.sunopta.com).

But resistant starch really took off with the popularity of low-carb diets. National Starch’s two resistant starches (RS2 versions) are being used in a wide variety of products, says Witwer, and are especially useful in whole grain products that lose some resistant starch during processing. Resistant starches also appear to resist dieting trends. Even if low-carb dieting falls by the wayside, the use of more fiber is likely to continue, especially as the problem of obesity demands attention.

Fiber enhancement is the major thrust of MGP Ingredients’ (www.mgpingredients.com) three-product line. Made by the Kansas State patent, MGP provides a wheat-based RS4 starch called Fibersym 70, a potato-based product called Fibersym 805 (produced by Penford Ingredients) and Fibersym HA, in conjunction with Cargill, made from high-amylose corn. Using the modification method, the products (which can be labeled as food starch modified), achieves very high fiber numbers—70 to 80 percent total dietary fiber.

Steve Ham, MGP’s product manager for Fibersym, acknowledges the low carb trend is slowing a bit, but the need for fiber in foods, both from whole grains and products made with refined carbohydrates, remains strong. “Our products have very low water holding, as little as a gram of water per gram of starch. This makes it very useful in lower moisture foods.” Ham doesn’t believe the “food starch modified” label is a roadblock, and that any consumer resistance is countered by the high level of total dietary fiber the product delivers.

ConAgra’s new Ultragrain (center) is made from white wheat, so it has the nutrition of whole wheat flour (left) but the look and texture of finely ground bleached flour.

A major use of resistant starches is in whole grain products, including bread, pasta, meal bars and similar foods. Other uses include low-moisture foods like cookies and dry pet foods.

One novel development is Ultragrain
from ConAgra Food Ingredients
(www.conagrafoodingredients.com). It’s a white whole-wheat flour from an identity-preserved white wheat, finely ground to produce a white bread with whole wheat nutrition. Tests indicate the fine milling has not reduced the resistant wheat function in finished breads.

A similar product, also from ConAgra,
is Sustagrain, a barley material that includes about three times the fiber of oats. It also can be used in whole grain foods to provide a different type of soluble fiber.

Perfection Bakeries, Fort Wayne, Ind., developed a line of carb-controlled bread products that did very well earlier this year. “We use two types of resistant starches in our carbohydrate-controlled breads, and they performed very well for us,” says Rod Radalia, technical services director.

While he believes low-carb dieting is beginning to wane, “We expect a moderate amount of carbohydrate reduction will become a permanent part of the product line.”  Radalia says he’s also discovered resistant starches provide some plusses, especially at lower levels to replace some of the refined flour. “We use them at about a pound-for-pound replacement level and [as a result] the different products carry different amounts of water.”

A key concept to remember is there are several types of fiber, and they appear to play different roles in nutrition, disease avoidance and weight control.

Americans are finding whole grain products palatable and satisfying. The current interest in whole grain products, triggered by the probable changes in the USDA’s Guidelines for Healthy Americans, suggests there will be more use of resistant starches, whole grains and fiber in food products. As the labeling and assay problems of the past are solved, they will become easier to use.

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