Increased market demands for functional food products pose a dilemma for R&D experts: How to make products more nutritious but not sacrifice taste or quality, especially when it comes to the typically indulgent snack foods? The incorporation of functional starches is key. 
According to the “Top 10 Functional Food Trends in 2010” survey by Elizabeth Sloane, Ph.D., 82% of consumers want snack foods that curb hunger and promote satiety. In addition, according to the Dietary Guidelines for Americans 2010, dietary fiber continues to be a nutrient of concern. Incorporating functional starches may be the perfect way to give consumers what they want, without sacrificing taste, texture and quality.
Fully-digestible (glycemic) starch, such as all-purpose wheat flour, has received a bad rap from consumers. Although glycemic starch provides energy in the form of glucose -- necessary for brain and red blood cell function -- it provides excessive calories if consumed in abundance.
To combat this problem, functional starches and starchlike components, such as resistant starch, ?-glucans, legume flours or polydextrose, are able to be added to, or partially replace, glycemic starches. Some of these even have properties that let them substitute for a portion of the fat in food products.
This also allows some of those products using functional starches to be marketed under one or more claims in comparing them to the standard version of the same product, without altering fat or protein amounts. When applicable, allowable claims include: “lower calories,” “higher fiber,” “helps lower blood cholesterol” or “enhances satiety.”
Increasingly, functional starches include those that are used to substitute for wheat and other gluten-containing sources. Through use of starches derived from legumes and seeds (such as amaranth, chia, quinoa, sorghum and millet); or from more mainstream flours from rice, corn or potatoes, the exploding gluten-free trend is bringing another level of functionality to baked and extruded products.
One recently developed source of functional flour is derived from microalgae. Although low in actual starch (less than one third total content) -- and most of the starch is in the form of fiber (soluble to insoluble in almost a 3:1 ratio) -- it’s a highly effective fat replacer at 50% lipid content. Plus, it is high in protein. This also makes it a suitable replacer of eggs in many formulations, especially baking. As a functional starch, it can only replace around 5% or so of standard starch in formulation, but that small amount allows for steep reductions in fat.

Adding Resistance

Starch that is resistant to digestive enzymes in the small intestine and enters the colon to be fermented by bacterial action is known as resistant starch. In this manner, although its structure -- and in many aspects, its function in food processing -- is that of a starch, its biological function is like fiber. In fact, according to the Institute of Medicine and Codex Alimentarius, resistant starch can be classified as a dietary fiber.
Four types of resistant starch have been identified: Type 1 is the physically inaccessible starch located inside of seeds or unprocessed whole grains; Type 2 is found naturally in just-ripe bananas, rice, barley, uncooked potatoes, high-amylose maize and other sources. Type 3 resistant starch is formed when starch is retrograded, such as in cooked potatoes, pasta and legumes; Type 4 is a chemically modified starch.
Because it also can improve the concentrations of beneficial bacteria in the colon, such as Bifidobacteria, resistant starches function as prebiotic ingredients. 
There are several types of resistant starches available to the food industry. While wheat and barley sources exist, perhaps the most prominent type is that derived from high-amylose maize. This is a functional starch made of approximately 60% resistant starch bred naturally from corn. The resultant flour is fine; white in color; neutral or “bland-tasting;” and odorless. Plus, low water-holding properties make this ingredient an ideal replacement for other “less-acceptable” dietary fibers in baked goods, pastas, cooked cereals or even some thickened beverages, such as smoothies.
Studies of baked and similar food products have demonstrated that high-amylose maize can substitute up to 25% of the glycemic starch while maintaining consumer acceptability. In fact, in some risen formulations, a very slight increase in volume -- about 3% -- has been reported.
“We found that partially replacing flour with high-amylose maize in muffins did not significantly affect the overall likeability when compared to the control muffin,” says Parakat Vijayagopal, Ph.D., an associate professor at Texas Woman’s University. 
Vijayagopal researches the beneficial biological effects of high-amylose maize in humans. Pointing out that adding high-amylose maize is an excellent way to boost fiber, Vijayagopal has determined that high-maize resistant starch-enriched muffins contained 5.5g of dietary fiber compared to 0.5g in the control product. 
“However,” Vijayagopal cautions, “completely replacing flour with high-amylose maize in a curry sauce produced a grainier texture that was not as acceptable to consumers as the sauce with flour.”
Research has shown that consuming 15-30g of resistant starch per day for at least four to six weeks (considerably more than the 3-8g Americans get in their daily diet) can improve satiety, increase insulin sensitivity and potentially reduce weight, according to Vijayagopal. 
And, noting the marketability factor, Vijayagopal avers, “Because resistant starch is a fiber, the benefits resonate with [consumers when it comes to] good digestive health.”

Starchy Fibers 2.0

As a non-digestible polysaccharide made of D-glucose units, (1,3)(1,4)-??-D-glucose -- a.k.a., ?-glucan -- is a functional starch in the form of a soluble fiber. It has been shown to decrease the risk of cardiovascular disease, lower cholesterol, attenuate post-prandial glucose levels and promote satiety. 
In fact, the cholesterol-lowering capabilities of ?-glucan prompted the FDA to allow food products containing at least 0.75g of ?-glucan per serving to bear cardiovascular health claims, provided they also are low in saturated fat, cholesterol and total fat. That said, a total of at least 3g of ?-glucan should be consumed daily for decreased cholesterol levels to be achieved.
Barley and oats are good sources of ?-glucan. The source of ?-glucan depicts the viscosity, solubility and physiological function of the ingredient. While ?-glucans can replace carbohydrates and fat, several challenges can arise when formulating products with ???-glucans. Namely, they are water-binding, viscous and can form gels in food products.
Molecular weight also matters when considering ?-glucan in formulation. ?-glucan forms that have a higher molecular weight form stronger gels more slowly and can alter the quality of the product. Yet, from a physiological standpoint, such higher-molecular weight ?-glucans could be more important to health. It should be noted that the molecular weight can diminish with mixing and fermentation time.
In an attempt to improve the nutritional quality of white bread, researchers Brennan and Cleary examined the replacement of glycemic flour with a high-molecular weight ?-glucan isolate from barley. Adding 2.5% ?-glucan decreased bread volume and height. This could be related to its water-binding properties. In contrast, a recent study by Singh, et al, published in Critical Reviews in Food Science and Nutrition, revealed that up to 0.3% of a highly purified oat ?-glucan in yogurt did not change the color, pH, viscosity or fermentation time. However, increasing the percentage to 0.4 did. These findings suggest that 0.75g of ?-glucan -- enough to make a health claim -- can be added to an 8oz carton of yogurt, and quality would be maintained.

Lupin Flour

While legume-derived flours have been experiencing a massive -- and welcome -- increase in application, a newer legume flour is coming into play. Praised 2,400 years ago by the famous Greek physician Hippocrates for nutritional superiority, lupins are a type of legume that has been a staple in the Mediterranean diet for centuries. Historically, lupins were incorporated into animal feed but have gained recent interest as a functional starch in the form of lupin flour: a gold flour with a texture similar to wheat-cake flour. 
Lupin flour can be added to baked goods, meat products and even ice cream. And, because it is yellow in color, it is an optimal replacement for eggs and butter in some formulations. Lupin flour is high in protein (40%) and fiber (30%) and has a low glycemic index. Substituting only 5% of glycemic starch in formulation with lupin flour can increase the protein level in the final product by 14% and fiber by 85%. 
These nutritional characteristics are believed to contribute to increased satiety; lower post-prandial blood glucose and insulin responses; and decrease total cholesterol. (The FDA has yet to approve any health claims for lupin flour.) 
In a 2010 study by Hall, et al, published in the journal Appetite, researchers gave 11 subjects a breakfast bread with 10% (7.7g) lupin flour. The glucose response was significantly lower when compared to white bread. While the energy intake throughout the day did not differ between the two breads, the lupin flour bread rated “acceptable” in the sensory analysis.
Consumers should be interested in products made with lupin flour, because it is both GMO- and gluten-free. Moreover, compared to soy flour, lupin flour maintains the bioavailability of certain minerals, such as calcium and zinc, because it contains half the amount of mineral-binding phytates as soy. However, as a legume, food products containing lupin flour should notify consumers of its potential allergen risk. Individuals with a peanut allergy are especially vulnerable, due to potential cross-reactivity with other legumes.

Poly In a Cracker

Developed in the 1960s, polydextrose is a very soluble, non-viscous glucose polymer made from corn, sorbitol, dextrose and citric acid. It was initially intended to replace the bulk sugar provides in food formulations, especially in baking. It now is used as a substitute for digestible starch and fat. 
Polydextrose also has been approved as a dietary fiber, because the highly branched chains and glycosidic bonds are not hydrolyzed in the small intestine. The partial, slow fermentation of polydextrose by bacteria in the large intestine increases stool weight to deliver a laxative effect.
The lack of taste and sweetness of polydextrose can help mask the off-flavors of other additives, such as vitamins and soy. This gel-forming functional starch also can enhance the mouthfeel and smoothness of foods. A study by Astbury showed the “creaminess” of chocolate milk increased as the amount of polydextrose increased.
In a 2011 meta-analysis published in Nutrition Reviews, polydextrose did not appear to affect fasting blood glucose or total cholesterol levels. However, decreased post-prandial glucose and triglycerides, and increased HDL-cholesterol have been reported. The FDA has approved polydextrose for use in all foods except meat, poultry, baby food and formula. 

The Form in Function

Amy Proulx, Ph.D., Contributing Editor
The functionality of starch seems to offer a straightforward choice in food product development. But, many recent scientific discoveries in starch chemistry are now available for product innovation, providing many benefits to the manufacturer and consumer. Functional starches are pushing the bar, when it comes to performance expectations, and are providing unique opportunities for improving food function, while delivering opportunities for using lower-cost ingredients, lowering fat or providing a clean label.
While generalized statements may be made about starch, application to application, each starch may perform differently. When selecting a starch for an application, ensure the product will be run through a representative processing regimen and shelflife test to guarantee the starch will tolerate and perform under the anticipated conditions. This can include full-freeze/thaw cycles, refrigeration, high-speed mixing and similar stress tests to ensure the product maintains the desired functionality.
There are a few general rules to apply when selecting a functional starch: Typically, larger starch granule size equates to better gel strength but less shear tolerance. Higher amylose content leads to higher gel strength. Higher molecular weight leads to higher viscosity (delivered by amylopectin).
Gel strength and viscosity work hand in hand but can have contrasting effects. High viscosity from amylopectin can contribute a stringy and slimy mouthfeel. But, putting the formulation through testing of all aspects can ensure the functionality of the starch meets expectations.
So-called “native” starches are not as old-fashioned as they once seemed. Through various methods, including advanced plant breeding, species selection, granule-size classification and sorting, starch manufacturers are now able to deliver a more custom approach to native starch. Given consumer demand for clean label products, suppliers are enjoying success from having developed a broader range of native starches that possess many of the functions of modified starches. These new native starch varieties provide similar functionality to modified starch, including enhanced tolerance to high shear and high-temperature processing, and better resistance to syneresis and gelling on refrigeration and freeze/thaw cycling.
One unique functionality recently developed in native starch is thermoreversible gelation. A number of suppliers are providing high-amylopectin waxy potato starch that has low viscosity during cook-up, then thickens and gels on cooling. This starch provides a number of advantages to the dairy and confectionary industry. The low viscosity during cooking allows for process flexibility, while the enhanced gelation on cooling is similar to gelatin, yet with a clean label. It is commonly certified as a kosher, halal and vegetarian ingredient.
In searching to extend the functionality of starch, lipophilic starches are esterified to possess hydrophilic and hydrophobic structure within the starch, and as such, are typically used for flavor encapsulation and emulsification. Octenyl succinic anhydride (OSA) starch is able to provide unique ingredient replacement for eggs, gum Arabic or sodium caseinate in a variety of applications.
Meanwhile, short-chain dextrins have unique film-forming characteristics and perform well in extruded or puffed snack foods, as well as in battering and breading operations. Selected from different plant sources, different short-chain dextrins will contribute film formation and provide fat-uptake reduction during deep-frying operations or provide protection against moisture resorption post-manufacturing in a variety of products.
Functionalized flours are blends of traditional wheat flours blended with modified starches, which are intended to provide an enhanced thickening or texture modification in products where flour would have traditionally been used. These enhanced flours are able to reduce fat content in cream sauces and gravies, and provide better refrigeration and retherming characteristics over straight wheat flour.
Starch suppliers are taking a more active role in the product development process, and in particular, have started directly focusing on the sensory metrics related to texturizing foods. They are able to directly deliver ingredient solutions specific to the attribute (gel formation, cling, creaminess, mouth-coating, thickness, etc.). Building a strong relationship with the ingredient supplier can help deliver a rapid solution, with less trial and error and quicker commercialization.
Dr. Amy Proulx is professor and academic program coordinator of culinary innovation and food technology at Niagara College, Canada. She also is the research coordinator for the Canadian Food and Wine Institute Research Centre, assisting companies with product innovation and technology solutions in the food and beverage sector.