Resistant Starch 101: A Guide to Understanding This Fiber-Like Starch

Resistant starches from several vegetable sources are available to up the fiber and lower your body weight.

By Food Processing staff

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About 25 years ago, scientists studying cereal grains discovered a starch that didn't exactly act like a starch; it acted more liker a fiber. Specifically, it was resistant to digestion and didn't break down until it reached the lower intestinal tract. Starch … resistant to digestion. Ergo: resistant starch.

Resistant starch occurs naturally in a number of agricultural products and in three forms. RS1 is prevalent in seeds, legumes and unprocessed or minimally processed whole grains. In RS1, the starch molecules are packed into dense granules and have more of the cell walls intact, creating a physical barrier that leaves few ends for the enzyme amylase to access.

RS2 contains much of the carbohydrate amylose. It, too, is packed into dense granules like RS1 but is not gelatinized – therefore, the starch does not break down and absorb water. RS2 therefore is digested very slowly. It's typically found in potatoes, corn, underripe bananas and flour.The third form of resistant starch, RS3, only becomes resistant when portions of the starch chain expand and then contract during food preparation or processing. It's another high-amylose starch, but the amylose forms during cooking, when the starch gelatinizes -- and at that point, it's digestible. However, cool the starch and the amylose condenses and becomes undigestible. Potatoes, breads and some cereals (such as corn flakes) are common food sources of RS3.

There is a fourth form of resistant starch, RS4, but it does not occur naturally. It's formed by chemical or heat treatment and has both soluble and insoluble properties and does not always behave like a fiber.

National Starch (www.foodinnovation.com) has been at the forefront of resistant starch research and promotion. Its Hi-maize resistant starch was introduced in 2002. Derived from high-amylose corn, it benefits weight and energy management as well as digestive and glycemic health. And of course it adds fiber to formulations.

Hi-maize reduces the caloric content of foods when it replaces flour. Many studies suggest it increases satiety. Unlike other types of dietary fiber, its fermentation in the large intestine increases satiety hormones (GLP-1 and PYY) over many hours. One clinical trial demonstrated that Hi-maize switches the body to burning more fat and fewer carbohydrates for energy.

The line has since been augmented with Hi-maize whole grain corn flour. National Starch also maintains www.resistantstarch.com with plenty of vendor-neutral content on the subject.

Tate & Lyle (www.promitorfiber.com) introduced its Promitor soluble corn fiber line to the food industry in 2007, and Promitor Resistant Starch emerged from the line one year later. Another corn-based product, it's 60 percent fiber. Tate & Lyle studies indicate it helps reduce oil pick-up in fried snacks, resulting in a 15-25 percent reduction in fat absorption and a potential reduced fat or reduced calorie claim.

Cargill (www.cargilltexturizing.com) turned to tapioca for the source of its resistant starch, ActiStar. The company claims ActiStar RT75330, in particular, has one of the highest total dietary fiber (TDF) levels of any natural resistant starch -- more than 80 percent, therefore contributing substantially to TDF daily targets and opening the door to dietary fiber claims. It's suitable for the formulation of healthy bakery products, not only for its fiber content but also for its caloric value of 1.9 kcal/g, which helps formulators lower the calorie content of foods.

"The very fine granulometry, the neutral taste and smooth mouthfeel of ActiStar tapioca-based starches avoid the unpleasant sandiness often experienced with high amylose corn-based resistant starch," Cargill marketing materials claim. "The low water-binding capacity and the low viscosity permit high inclusion levels whilst avoiding significant formulation changes."

Wheat is the source of the resistant starch from MGP Ingredients Inc. (www.mgpingredients.com). Fibersym RW is an RS4 resistant wheat starch, "a convenient and rich source of invisible dietary fiber that can be formulated with minimal processing adjustments in a wide array of finished products, including white bread and whole grain bread products, high-protein, high-fiber bread products, pasta and noodles and extruded cereals."

Fibersym RW allows a minimum total dietary fiber of 85 percent. With neutral flavor and color impact, smooth texture and low water-holding properties, fiber content can be increased in a wide variety of manufactured foods, especially those geared toward weight-reduction.

The next "fiber of the future"?
Newer sources of fibers that give the double advantage of health properties and needed performance characteristics such as structure and stability are becoming trendy contributors to the overall digestive health boom. Gum Technology Corp. (www.gumtech.com), Tucson, Ariz., followed a burst of interest in an Asian yam, Amorphophallus konjac, by releasing Coyote Brand Konjac, a refined konjac flour.

The tuber has a natural mannose-glucose polysaccharide and is used as a thickener and stabilizer in food, but it gained interest lately for pharmaceutical and health applications.

Structurally, konjac is used as a dough conditioner and extender in baked goods; for moisture control and improved freeze/thaw in noodle and dumplings; as a gelling agent and texture enhancer for sweets, dairy, beverages, even meat and meat analogs.

"Hydrocolloids such as konjac, tara gum, guar, locust bean gum, gum arabic, etc., consist of mostly soluble dietary fiber," says Janelle Litel, Gum Technology's director of marketing. "Tara gum is 82 percent dietary fiber — 72 percent soluble fiber and 10 percent insoluble fiber. It is typically used at low concentrations in standard food applications to achieve functions such as emulsification, water retention, texture, shelf life extension, etc. However, it also can be used at higher concentrations to increase the fiber content."

Litel explains, "The type of fiber and the content, viscosity, water absorption, protein interaction, pH stability and ability to create clear solutions are all characteristics you need to take into consideration when developing a new product using fibers. For example if you want to add soluble fiber to a beverage without increasing viscosity, you would want to use something like gum arabic. Gum arabic also helps stabilize the system and add suspension. If you want to add insoluble fiber, then something like sugarcane fiber [cellulose] will be a great option. You can even combine gum arabic and sugarcane fiber and use it at high enough concentration to prepare a high-fiber beverage with a good mouthfeel."

Fiber has become more prominent in dairy products, especially milk substitutes and yogurt. "If you are developing a yogurt, especially if you are making a low-fat or nonfat product, you want to add fibers that also help stabilize the proteins and add some texture," says Litel. "Usually a blend of pectin, inulin and cellulose gel will work well."

According to Litel, the right combination of fibers can help to increase shelf life in baked goods by reducing moisture migration, for example preventing moisture from moving from the cake into the icing. (or even from the icing into the cake). "Some products that will work well in these types of applications are oat fiber, milled flaxseed, fenugreek gum, xanthan gum and guar gum," she says.

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