Starch, The Complex Carbohydrate
Starch is the principle carbohydrate in every baked product. It is also the main “complex carbohydrate” in these foods. That makes formulation of today’s popular reduced-carb foods easier than it might seem.
“The impact of low carb on the food industry will be felt for years to come, as the consumer focus on health and wellness continues to affect all categories,” said the business development manager for nutrition at a major East Coast-based starch processor. She quoted recent research that found as many as 30% of all Americans limiting their carbohydrate consumption.
“Now is a great time to be offering scientifically substantiated, great-tasting, health-promoting carbohydrates into the consumer-driven food industry,” she continued. “I believe the magnitude of this trend could be a once-in-a-lifetime opportunity.”
SIMPLE AND COMPLEX. Unlike protein, which is made up of different amino acid units, starch has a simple structure: one glucose unit attached to the next. That’s how plants store energy. No matter their source, all starches consist of amylose, long chains with few branches, and amylopectin, intricate branched structures. The difference comes in the ratio of these two forms and the treatment, if any, given the starch during processing.
But do not confuse starch with other carbohydrates such as fructose, dextrose (glucose) or sucrose. Such “simple sugars” consist of one or two saccharide units only. Even the oligosaccharides, consisting of eight or more dextrose units, are uncomplicated when compared with amylose and amylopectin. These are large molecules: Amylose is linear, with a few branches, and can contain more than 2,000 glucose units, linked into a chain with a molecular weight of 250,000 to 1.9 million. Highly branched, amylopectin is even bigger, estimated to have a molecular weight between 1 million and 100 million making it one of nature’s largest molecules. The size of the molecules differs according to plant source, and starches extracted from tubers such as potatoes or yuca (tapioca) are bigger than those from cereal sources.
Because of their size, starch molecules take time to digest in the human gut, thus slowing the body’s glycemic response. Some are so highly branched and tightly bound that they function like fiber.
What are the functions of starch in doughs and finished baked foods? It dilutes the gluten to a desirable consistency. It furnishes sugar to fuel the yeast through amylase action on damaged starch granules. It provides a surface suitable for strong union with the adhesive gluten. And it manages water in several related ways.
Compared with liquid applications, such as fillings, dough is a relatively low-moisture environment, so starch absorbs water from the gluten, thus permitting further stretching of this protein film. When gelatinization of protein and starch occurs, both become rigid. The films break becoming permeable to gases, but the structure remains stable so the baked item doesn’t collapse on cooling.
The long,branched starchmolecules bind water during mixing and baking but lose this water over time. When this happens, the starch recrystallizes, or retrogrades, to cause staling.
WHY USE? Given that starch is the majority component of wheat flour, why add starch to the formulations of baked foods? Its benefits include properties of gelling and moisture control. It adds viscosity to systems, thus giving bakery mixes the homemade feel during preparation and aid in maintaining the distribution of particulates throughout doughs and batters.
“With the diversity of today’s highly functional starches, it is possible to maintain desired taste and texture of products through many challenges in processing, handling and shelf life,” said the marketing communications assistant at a Midwestern processor of specialty wheat ingredients.
Starch provides a variety of properties, depending on its plant source, form and treatment. Native starches, for example, will thicken and gel when heated, building system viscosity and binding water. Modified starches can be designed as “thinned” starches, with functionalities involving setting, solubility, adhesion, gel strengthening and film forming. They also have low viscosity when heated. Modified to be “stabilized” starches, these materials exhibit film-forming, emulsion, viscosity, texture, stability and gelling functions.
RESISTANT STARCH. Several years ago, researchers discovered that some forms of starch found in baked foods and snacks actually resisted digestion and functioned in the body more like insoluble dietary fiber than carbohydrates. Resistant starch can form when starchy foods are heat processed. Also, it occurs naturally in some grains. Analyzed using AOAC Method 991.43, an accepted method for documenting the fiber content of foods for labeling purposes, resistant starch gives readings equal to materials containing 40% total dietary fiber (TDF).
“Resistant” starch is now offered as a separate ingredient. Compared with traditional fibers, resistant starch imparts better expansion, crispness and mouthfeel to fiber-fortified foods as well as having lower water-holding capacity, according to its manufacturers.
First on the market were natural resistant starches derived from highamylose corn and offered by a major food starch producer located on the East Coast. “These starches have been used as fiber sources in a variety of foods for the low-carb market,” said the company’s business development manager for nutrition, citing their natural identity and strong clinical support as well as ease of use. The starches qualify as type-2 resistant (RS2) and are the only commercially available starches in this category, according to the company.
“More than 40 published, peerreviewed, human clinical nutritional studies have shown that natural RS2 starches contribute to specific digestive health and nutritional benefits,” she continued. “No other resistant starch has been studied this extensively in humans. Our clinical research program has proven that not all resistant starches are the same. Different types of resistant starches are now being introduced to the market, but the scientific evidence supporting natural RS2 starches is not applicable to chemically modified type 4 resistant starches.”
The studies demonstrated the benefits in weight maintenance, energy management, immune system support , digestive health and even diabetes. This constitutes important clinical evidence supporting a wealth of labeling claims as the market evolves toward better-for-you carbohydrates, according to the business developer.
In contrast to most fiber ingredients as well as native or modified starches, resistant starch absorbs water at a much lower rate. A new resistant starch, made from wheat starch and introduced during the past year by a Midwestern processor of specialty grain-based ingredients, is not only clean in flavor, white in color and smooth in texture, but it also binds very little water — an ideal starch for preparation of fiberenhanced and low-carbfoods. This year, the same company introduced a resistant potato starch, as well.
Researchers at this Midwestern company report working with applications using both its wheat-based specialty proteins and resistant starches. “We confirmed the compatibility and enhanced functionality of mixtures of wheat starches and proteins,” the marketing communications assistant stated. “Many of these applications are atypical of starch applications prior to the interest in low-carb foods.
“The formulas of wheat flour-based products require no major alterations because the added resistant wheat starch is compatible with the starch already present,” he continued. “We’ve confirmed this not only in yeast-leavened and chemically-leavened bakery products, but also in non-leavened products such as pasta.”
NATURE, MODIFIED. To produce starch, manufacturers first mill the grain or tuber source to free the starch from plant cells. It is then centrifuged to remove the fiber and purified to separate the protein and soluble material. Corn is also treated to remove its oil content, and wheat must be processed to extract the gluten.
Depending on its plant source, native starches possess different properties. Undamaged native starch is normally insoluble in water, but when heated they swell at different rates and produce pastes of varying structures and viscosities.
To further enhance the functionality of starch, food starch manufacturers apply physical and chemical means for changing the properties of native starches. The chemical methods include acid hydrolysis, oxidation, dextrinization, esterification and etherification. Physical modification involves cooking the starch and then roll-drying or spray-drying it. The results are watersoluble, instant-thickening, easily dispersible starches, with some designed to swell in cold water. Pregelatinized starches are pre-cooked alternatives to cook-up starches.
The functions achieved help build or retain the textural profile of food products that satisfy consumer expectations. Take the example of modified tapioca starches. “They are used in frostings and glazes to build viscosity and binding,” explained the sales and marketing manufacturer for a Midwestern supplier of specialty grain-based ingredients. “They also mimic fat in baked foods. The starch has good moisture binding and can provide a creamy texture.” The company notes that its modified tapioca starch has a similar melt curve to fat and can also act as a partial replacement for nonfat dry milk.
“Specialty starches play a unique role as the backbone of texture in a wide range of food products,” explained the marketing program manager for food products at a major East Coast starch processor.“Whenever you alter the nutritional profile of foods, you directly or indirectly impact the texture or eating quality of that food. It is clear that consumer preference for foods are driven primarily by taste and texture — the sensory experience of eating the food.
“So whether it’s low fat, low sugar or today’s low carb, the long-term success of these new products is contingent upon the formulator’s ability to match the desired nutritional profile while not negatively impacting the flavor and texture attributes expected by the consumer,” he stated.
NEW APPROACHES. Starch processors continue to explore new ideas in modified starches. Because convenience is so important to consumers, instant starches that shorten home prep time get high-profile attention from developers. Most of these cold-water-swelling, pregelatinized starches are targeted at consumer and food service mix applications, but a recent introduction in this category is aimed at the bakery market. Not only do cold-prepared fruit, cream or jam fillings reduce energy costs in the shop, but the starches used deliver superior mouthfeel and body, set faster and are more rigid in their gels than conventional pregelatinized starches, according to the manufacturer.
An interesting development is the blending of starches to build functional performance. The food products account manager for a major East Coast-based starch manufacturer described as “many faceted” the advantages of combining several different starches into one, all-purpose, multifunctional ingredient. “By doing this, we eliminated the need for storing multiple types of starches in the bakery and reduced the training and knowledge associated with using those many starches properly,” he said.
Agglomerated starches, according to a Midwestern supplier of specialty grain-based ingredients, have benefits for the bakery user, too. “They are dustless and free-flowing,” explained the company’s sales and marketing manager. “They are manufactured to provide rapid dispersion with minimal agitation and without lumping in fillings and toppings.”
NATURE UNCHANGED. Some consumers, however, view the term “food starch modified” negatively and reject food products when they find it in the ingredient listing.Also, product formulators seeking to clean up food labels have questioned the use of modified starches.
But how to replace the functionality of these ingredients? The answer, of course, is to use native starches, those obtained “as is” from plant sources and refined without chemical modification. To find functionality beyond the commonplace, however, the starch processor must dig deeper and search wider for sources of supply.
“Functional native starch offers processing tolerance and freezethaw stability previously available only from modified food starch,” said the East Coast-based marketing program manager. His company produces a line of such starches that meet the needs of the “clean-label” driven natural foods market. “They allow the development of the highest quality clean-labeled frozen and refrigerated products without sacrificing product quality and processing performance,” he said. “In addition, these products offer a cleaner flavor release, with less pastiness, than traditional modified starches.”
Of course, when home-style appearance and taste is the desired target, say for pie fillings or pastry cremes, formulators can turn to flour itself. Starch accounts for nearly three-quarters of the content of regular wheat flour. Flour added to such mixtures will thicken and gel the fillings, and it adds its own flavor and a creamy off-white color. After all, that’s the way “mom’s peach pie” is supposed to look and taste.
In the long run, consumers hold the power of the pocketbook, buying products made the way they like and ignoring those that are not. When the formulator chooses which starch to use in a given product, the marketer must judge the final product’s marketplace potential based on knowledge about the customers. Lately, that understanding has been challenged by low-carb diets. It’s not known whether this will translate into permanent dietary changes to reduce the incidence of obesity and diabetes, but if it does, the complex carbohydrates of starch offer an important key to unlocking new product choices.