Something interesting happened during the Atkins assault on baked foods: The industry discovered the value of fiber and, especially, resistant starch. As the food business moves beyond the low-carb fad, opportunities for better-for-you formulating continue to expand. Now the challenge is to figure out how best to put resistant starch to work.
Resistant starch exists in grains, fruits and some processed foods and gets its name from the fact that it resists digestion (enzymatic hydrolysis) in the small intestine. Because it is fermented by the bacteria in the colon, this form of starch can aid gut health by producing short-chain fatty acids, lowering colonic pH, decreasing intestinal transit time and increasing fecal bulk. In baked foods, resistant starch often functions as a flour replacement, thus lowering calorie and carbohydrate counts. Resistant starch also has been used to "top off" the dietary fiber content allowing foods to make fiber health claims.
The physiological benefits of resistant starch, similar to those of dietary fiber, are many, but this category of ingredients also has unique functional properties in foods, properties that traditional insoluble fibers lack. Resistant starch is especially appropriate for grain-based low- and moderate-moisture foods, according to National Starch Food Innovation, Bridgewater, NJ. Other manufacturers confirm that its physical properties, particularly its low waterholding capacity, facilitate processing and improve crispness, expansion and texture in the final product.
National Starch counted more than 120 published studies conducted during the past 15 years that show numerous health benefits from consumption of its Hi-maize natural resistant starch. And the latest science may show even greater reach along health lines. "At the recent whole grains conference, a researcher from Australia said dietary benefits from whole grains may be due to their resistant starch content," recalled Rhonda Witwer, business development manager, nutrition, National Starch Food Innovation.
WHAT IS RESISTANT STARCH?
Nature packages starch molecules in tidy granules. Mechanical action and enzymes break the granules to release starch, a complex carbohydrate.
"Normally, in grain-based foods, starch granules will gelatinize (hydrate) either partially or fully," said Dale Bertrand, manager of research and commercialization, AVEBE America, Inc., Princeton, NJ. "This opens them up to enzymatic digestion in the upper gastrointestinal tract. Resistant starch is different in that, although partially hydrated, it is still resistant to enzymatic digestion, and a significant portion passes through to the lower tract where it is fermented by the local flora and fauna."
(Because resistant starch is not digested by the human gut but by its microorganisms, it is considered a prebiotic. These properties will be explained in the September edition of Food Ingredient Solutions.)
When AACC International revised its definition of dietary fiber in 2000, the cereal science group included resistant starch under "analogous carbohydrates," explained Ody Maningat, Ph.D., vicepresident of application technology and technical services, MGP Ingredients, Inc., Atchison, KS. "Analogous carbohydrates are materials not necessarily intrinsic to a part of a plant as consumed but that exhibit the digestion and fermentation properties of fiber," he said.
"Resistant starch is different physiologically from other forms of starch when consumed," Ms. Witwer said. "Using resistant starches made from high-amylose corn, we can actually deliver two times the daily requirement of fiber, confirmed in a human clinical study. Resistant starch results in less flatulence because it ferments so slowly compared with conventional soluble fibers. That study, which has been completed but not yet published, found you could feed as much as 45 g of fiber as Hi-maize without side effects. This will help people conform to the new Dietary Guidelines recommendations."
She pointed out, "Evidence in the literature says different sources and structures of resistant starch behave differently."
Resistant starches are categorized into four types depending upon the mechanism of enzyme resistance. They differ in their resistance to digestion and, thus, have dissimilar processing and dietary effects.
RS1 starches are protected by being entrapped within the starch granule itself. Dorothy Peterson, product line specialist for starch, Cargill, Minneapolis, MN, described the RS1 examples from her company as being milled corn and wheat.
RS2 starches are in native, ungelatinized form, primarily high-amylose starches, such as National Starch Himaize and Novolose or AVEBE’s Paselli FP line of potato starches. Roquette also identified banana starch as a RS2 type.
RS3 starches are retrograded forms. Commercial RS3 products are based on high-amylose maize and tapioca. Some RS3 starches form during extrusion or heat-processing of grain-based foods.
RS4 starches are chemically modified. The first of these were produced from amylose sources, although starches from wheat, potato and tapioca are now being so modified.
Commercially, RS2 was the first form to be introduced and, with RS3 forms, are the most widely used. RS4 is the newest to enter markets. RS1 has been part of grain flours all along.
Recently, a new class of ingredients has been added to the mix: resistant maltodextrins. "Roquette recently developed Nutriose FB, a new dextrin that offers all the benefits of resistant starches and, in addition, is a soluble fiber," said Emily Lauwaert, marketing, food business unit, Roquette Freres, Lestrem, France, with a US subsidiary at Keokuk, IA. Because it is only slightly digested in the small intestine and then slowly fermented in the colon, it fits the functional pattern of resistant starch with a low glycemic response. Fibersol-2, offered through a joint venture of ADM and Matsutani, is a digestionresistant maltodextrin. And AVEBE describes its Paseli FP as a "resistant starch alternative."
"The functionality of resistant starch depends on its molecular structure, on the amylose-to-amylopectin ratio," said Mark Matlock, senior vice-president, food research, ADM Specialty Ingredients, Decatur, IL. "And resistant starch is not 100% fiber. Some of its contents function as starch."
SOURCE AND USE
Commercially available resistant starches are derived from botanical sources: wheat, potatoes, high-amyose corn and tapioca. "The biggest differences include water-holding capacities and levels of dietary fiber," explained Steve Ham, director of marketing for specialty ingredients, MGP Ingredients.
"MGPI’s Fibersym resistant starches have the highest levels of total dietary fiber (TDF), so a lower usage level is needed when compared to others," he continued, noting that MGPI starches can be used as a partial or complete replacement for flour in bakery applications.
The source of the resistant starch plays a big role. "Much of the functionality of resistant starch depends on the base from which it is made," said Cargill’s Ms. Peterson. This fact was confirmed by Mr. Ham, who added, "Matching the botanical source to the food product is beneficial. A resistant wheat starch, for instance, is ideal for use in wheat flourbased food products."
"What is the true end objective?" AVEBE’s Mr. Bertrand asked. "Carbohydrate reduction? This can be accomplished by fibers sourced from potato, oats or wheat as well as resistant starches. Prebiotic activity? The manufacturers of inulin have proven that not all prebiotics have to survive the Prosky test to be highly effective in the gut."
Because resistant starch and conventional food starches function in different ways, their applications also differ. Ms. Peterson observed that traditional corn-based starches have not seen much use in bread but are more focused on cakes, muffins and fillings. "A lot of starches act as thickeners and binders, a detriment in bread," she said. "With resistant starch, you are replacing a portion of the flour to supply additional fiber. Resistant starch is different."
Water-holding capacity varies, as Dr. Maningat observed: "Wheat- and potato-based Fibersym ingredients have the lowest water holding capacity of 0.7 to 0.8 g water per g Fibersym versus the much higher water holding capacity of other resistant starches (1.2 to 2.5 g water per g resistant starch)." Formulation is easier because no adjustments in liquid levels are required, and this functionality actually enhances the crispness of some finished foods.
"When a fiber takes up moisture it changes the bake time," said Stan Andrews, Ph.D., manager, bakery ingredient applications, ADM Specialty Ingredients, explaining the difference between fiber-enriching ingredients and resistant starch. "Most fibers absorb three to 12 times their weight in water. Yet when resistant starch is water soluble, it won’t interfere with the waterbinding functions of other ingredients."
"You want the resistant starch to be similar in water-binding characteristics to the flour it replaces," Ms. Peterson said.
Resistant starches that test high in TDF such as Roquette’s Nutriose FB 06 at 85% fiber content or ADM/ Matsutani’s Fibersol-2 at 90% make it possible to enrich products with fiber to optimum recommended levels and to support label claims.
Like many other ingredients, resistant starches come in the form of a finely particulated white powder. They are handled and stored just like other native and modified food starches. "In bakery products, pasta, noodles, snacks, breakfast cereals, dairy products and confectioneries, resistant starch is conventionally added at the front end of the process together with the other dry ingredients prior to adding liquid additives and further processing," Dr. Maningat said.
"Most clients want to minimize their formula adjustments," Ms. Peterson said. "In most products, resistant starch is invisible." But she cautioned that unless using a supplier’s formulation, some trialing is essential to deal with water control and dough rheology.
She has recently noticed a change in the approach taken in new product development. "The current formulating climate is so different from low-carb. Formulators are taking time to make their products taste good and look good. I have also noticed that the food companies tend not to stray too far from what the consumer would expect of a conventional product. And that takes tricky formulating to get the right system to deliver a product the consumer will appreciate."
"Start with the claim you intend to make," National Starch’s Ms. Witwer advised product developers. "If you are trying to reach five or six grams of fiber per serving, you can’t have a lot of water-holding activity." This is where resistant starch really pays off because it generally has lower-water holding capacity than other fibers, she stated.
Bakers considering nutritional claims would benefit from use of insoluble and insoluble fibers, according to Roquette’s Ms. Lauwaert, who placed her company’s Nutriose among soluble choices. "These fibers are easy to dissolve and disperse in the dough," she said. "They would reduce the effect of insoluble fiber on dough characteristics such as water binding."
Usage levels range from 5 to 20% of dry ingredients for bread and buns, as long as protein (gluten) content is adjusted, and 3 to 20% in baked sheeted or extruded snacks. "In cookies, brownies and tortillas, you can do a 1:1 substitution of resistant starch for fiber," Ms. Witwer said.
Whole-grain foods offer additional opportunities for resistant starch. "We see whole grain as an important way to bring more fiber into the diet," Ms. Peterson said, "and you can combine whole grains with resistant starch for a better product with more consumer appeal."
It’s also important to recognize that resistant starch is starch, a comment made by several sources interviewed for this article. Resistant starch itself does not change the viscosity of batters and solutions, yet some may gelatinize during baking or processing. "It may work OK in the lab, but be aware as you go out into the high-speed, and even not-so-high-speed, processing environment," ADM’s Mr. Matlock cautioned.