Building Texture with
Gums and Starches
January 1995 -- Cover Story

By: Scott Hegenbart
Editor*

*April 1991-July 1996

  Gums and starches serve a wide variety of functions, ranging from stabilizing to replacing fat. In many foods, these ingredients also are useful for building and/or modifying the product's texture.  Because so many types and variations of gums and starches exist, selecting the correct ingredient for the desired result can be challenging. Examining fundamental food structure can give product designers an edge when texturizing with gums and starches.What's the big deal?  During a project, product designers frequently become consumed with issues regarding flavor, appearance and manufacturing, while texture is often an afterthought. This is unfortunate because texture plays a role in many critical product characteristics beyond just mouthfeel.  "When working with texture and stabilization, you're building the framework of the food system," says Chuck Bullens, senior research food technologist, FMC Corp., Princeton, NJ. "This framework then can be used as the delivery system for the flavor and appearance of that food product."  Product texture can influence any of five general areas. First, and most obvious, is texture's influence on eating quality. Next, texture affects the processing of a product. A filling with an overly thin viscosity, for example, won't deposit neatly onto a baked product. For the same reason, starch-molded candies can end up with "tails." Products that are too thick can simply be unprocessable.  "Let's say you develop a fat-free product that must be processed on plate heat exchanger," says James Carr, Ph.D., technical director, SBI, Waukesha, WI. "You can develop a fat-replacement system that builds viscosity to get the right mouthfeel, but the product will be too thick to go through the exchanger plates."  Third, texture affects a product's flavor profile. Being carbohydrates, gums and starches influence flavor release by binding or masking certain flavor components while readily releasing others. Many researchers have studied carbohydrate binding of flavor components in hopes of finding a way to avoid adding overages of flavor ingredients. Some of this research, however, is being used in a completely different way.  "The whole fat-reduction area has changed the way we look at flavor release," says Carr. "Now we're actually looking at ways to slow the flavor profile by using texture as a tool. The goal is to match how flavor releases in a full-fat product."  Next, texture is related to how stable a product is. If a multiphase product separates, for example, the texture will be wrong. Similarly, a product that exhibits syneresis during distribution or one that forms crystals during frozen storage will lack the desired eating qualities.  The fifth and final area that texture influences lies in the color and appearance of the product. "Visual impact is noted in some of the texture definitions," says Carr. "Although it may seem indirect, the product texture affects color, smoothness and sheen."Elements of texture  Despite its other areas of clout, texture's major role is its influence on a food product's eating quality. Considering how important this is, it is surprising that no universal texture definition exists. This isn't for lack of trying, however. A look at the many sources for information on texture reveals that eating quality consists of many textural influences.  "Texture is the combination of a product's physical appearance along with sensory/tactile manifestations that one receives when one looks at a product and starts to consume it," says Jim Zallie, marketing manager, National Starch and Chemical Co., Bridgewater, NJ. "This influences the overall organoleptic aesthetics of the product."  Although many researchers concentrate on the mouthfeel/tactile elements of texture, the visual sensory impact can be just as critical.  "You can see the expansion in a cereal product, you can see the cell structure of a cake, and you can see the springiness of a jelly product," says Hank Izzo, Ph.D., project supervisor, National Starch and Chemical. "It also gets into sound- the crunch you get when you bite into a potato chip versus a pretzel, for example. Texture also has to do with the way the material feels in the mouth as it dissipates."  Texture affects all five senses during product consumption. Precisely how texture does this can be identified and studied using the Spectrum descriptive analysis method, which is described in "Putting Mouthfeel into Words" in the August 1992 issue of Food Product Design. In brief, the Spectrum analysis breaks down the eating experience chronologically and describes the textural sensory experience at each of seven steps.  The first step is surface texture. This includes how the food initially feels to the lips and the general textural appearance of the product.  The next two steps are partial compression and first bite. These are mechanical properties that, together, determine the springiness, overall hardness and the cohesiveness of the product.  As this bite of product is eaten, the evaluation moves into the first chew and chew down stages. First chew reviews many qualities of the first bite and includes adhesiveness in the mouth and the density of the food. Chew down shows the sample's moisture absorption and cohesiveness once the food is broken down further and mixed with saliva.At this point, the flavor release of the product should be evaluated.  As chewing continues and the product disappears through swallowing, the overall moistness of the product and how pleasant it is to eat become more important texturally. This sixth stage of texture evaluation is the melt rate. Once the product is swallowed, the seventh evaluation stage - residual - reviews the way the product coats the mouth and/or leaves remaining particles.Hydrocolloids on the scene  At each of these stages, gums and starches play a role in the product's texture. They do so by influencing three types of properties: mechanical properties, geometric properties, and the overall moisture and fat content.  "Among these three, hydrocolloids affect viscosity and flow," says Florian Ward, Ph.D., director of research and development, TIC Gums, Belcamp, MD. "They also influence flakiness and graininess because they can form films that are either flexible or brittle. Third, they have the ability to bind moisture and fat."  On a general level, all starches and gums bind moisture, thicken, and form gels and films. Although they function in an aqueous environment, their influence on texture is much broader than building viscosity in a fluid system. A helpful way to look at the overall hydrocolloid influence is to view all foods as consisting of one or more of the following four basic structures: viscous fluid, gel, foam and film.  "In a sense, these are the only food structures that exist," says National Starch's Zallie. "Now you can break this down more easily to look at the textures that hydrocolIoids can impart along these four food structures."  How hydrocolloids create these structures can be viewed as a continuum. First, a hydrocolloid builds viscosity. Taking viscosity further results in a gel. Whipping air into either of these structures creates a foam. Desiccating any of the previous three structures forms a film.  In viscous fluids, hydrocolloids contribute to the degree of viscosity and the type of viscosity. Certain ingredients will produce a very sturdy viscosity that gives a rich fullness; others will break down rapidly. In addition, viscosity-building hydrocolloids may contribute opacity or even color to a product.  Color and opacity also are important in gels. Depending on the ingredient and its concentration, gel texture can run from soft to hard, and elastic to brittle. The reversibility of a gel determines the way it melts away in the mouth.In a foam, the continuous phase is a liquid. A hydrocolloid in this continuous phase will allow the designer to manipulate the viscosity and, subsequently, how the bubbles in the foam behave.  "When bubbles easily coalesce, the film in between the bubbles is thin," says National Starch's Izzo. "By thickening this film with a starch or a gum, you can keep those bubbles in place to get a thicker, more stable foam."  The basis of film formation is having a continuous layer of molecules that can interact strongly enough to inhibit the passage of either moisture or even gasses like oxygen. Such a continuous layer is formed by linear molecules found in many hydrocolloids and the linear amylose starch molecule. Branched hydrocolloid molecules can't align together. Films can be found in the cell walls of baked products, where they contribute to product structure and moistness.Beyond the basics  Although most foods derive a major portion of their structure from the characteristics of at least one of the basic food structures, these four categories don't provide the total picture. Many foods are actually combinations of two or more of the basic structures.  Fluid food products such as beverages, dairy foods, and dressings and sauces frequently contain starches and gums to build the desired product body, which follows the viscous fluid basic structure model. The hydrocolloid doesn't have to make the product thick to be critical to the texture, however. In many beverages, the desired effect often isn't thickness, but a touch of richness and mouthfeel.  "This is especially true for the lower solids products, the products that are not 100% juice with pulp added," says Mark Freeland, director advanced hydrocolloids, Rhône Poulenc, Cranberry, NJ. "When you add hydrocolloids to provide mouthfeel, you need something that is extremely pseudoplastic, something that will lose viscosity rapidly with minimal shear. Swallowing involves minimal shear, and you want something that has an initial impact of body and mouthfeel but dissipates rather rapidly."Beverages that contain fat, such as shakes, use hydrocolloids not only to thicken, but to maintain smooth texture by helping to maintain the oil-in-water emulsion of the liquid.  "Gum acacia is a protein complex, and certain groups on the protein molecule give it surfactant properties," says TIC's Ward. "An emulsion stabilized with it will provide a fat-like coating similar to the oil itself, which then gives you a nice smooth mouthfeel."  Dairy products follow the basic structures fairly closely. Fluid products behave like viscous fluids; sour cream and yogurt have gel-like structures. Frozen desserts, on the other hand, require a bit more thought because they are a stabilized emulsion that has been aerated to a foam and frozen at the same time.  "Ten percent butterfat ice cream mix is 60% to 62% water, and hydrocolloids structure that water," says Freeland. "Although they're more frequently recognized for ice crystal control, hydrocolloids will provide chewiness and a sense of creaminess and richness."  Sauces and dressings, like many of the other fluid products, exhibit basic viscous fluid structure. They also make very specific demands on the hydrocolloid. A salad dressing must behave as a different basic structure while being used. The dressing must first be a viscous liquid in order for the consumer to shake the product and pour it onto a salad. Once there, it must cling to the lettuce without being unpalatably thick. A loose gel structure created by a shear-reversible hydrocolloid, such as xanthan gum, can provide this dual-structure behavior.  "The role of pseudoplasticity here is very important because the shear energy of pouring is relatively low and you want to be able to pour the dressing out of the bottle," says Freeland. "But once you remove the shear, you want it to set up."  As with beverages, the potential textural effects provided by gums and starches to dressings and sauces can be subtle. Dressings ordinarily have a smooth texture, while tomato sauce or, to a greater extent, applesauce has a rough, pulpy texture. The hydrocolloid selected has a direct effect on this quality in the product.  Starch granules vary in size depending on the source. Potato starch has large granules that can provide pulpiness, while rice starch has very small granules that contribute a smooth texture to a food product.  "You can do the same thing with particle size in gums," says Freeland. "Guar gum and locust bean gum are not true solution polymers; they are a colloidal suspension. By changing the gum's particle size from 100 mesh to 80 mesh, you can create a rough surface and add pulpiness to either a tomato or pizza sauce."  Low moisture foods include products such as bakery foods, cereals and snacks, and confections. Unlike fluid foods, the basic structures involved in these categories are less obvious and often change while the product is being made. Consequently, the performance requirements of the texturizing system evolve, as well.  Bakery products have low moisture levels only after processing. Whether they're made from a dough or a batter, they start out as viscous liquids. At this stage, the viscosity control of a hydrocolloid can help achieve optimum rheology for processing. While the product is proofing and baking, leavening gases turn the liquid to a foam.  "If the batter is too thin and there's not enough structure when the leavening gases are released, the product will not rise to the proper volume," says Freeland. "Hydrocolloids help the volume of the cake by working with the batter viscosity to make sure the cell walls don't rupture."  Improving gas retention with a hydrocolloid is especially useful for "light" breads. Here, the addition of fiber may interrupt the continuous phase and make the cell structure weak. A hydrocolloid can help reinforce the cell structure and allow the product to stand up to processing.  Because baking removes moisture, the cell walls then desiccate and acquire the properties of a basic film structure. So, the film-forming properties of a starch or gum certainly will affect the final texture. If the hydrocolloid forms stiff films, the product can have a firm, crunchy texture. A more flexible film can help a product be soft or chewy. A softer product also may be possible because the hydrocolloids bind moisture. This may even help improve the product's shelf life.  "After baking, the hydrocolloids help retain moisture and can increase the number of days the product can be stored at the proper softness level. Hydrocolloids also may actually help retard starch retrogradation," says Freeland. "This isn't infinite; you may be looking at five days versus three."  The moisture-binding property of hydrocolloids is the primary reason they're used in reduced-fat bakery products."Oil is really responsible for the texture and moistness of baked products, and taking it out makes a drier product," says Meera Crain, senior technical service scientist, Avebe, Princeton, NJ. "You can help alleviate that by adding a starch to bind water."  Using hydrocolloids this way, though, requires establishing a delicate balance. Adding just enough holds the moisture and maintains texture, while too much will cause the product to grab too much moisture and make it overly dense.  Like bakery foods, cereals and snacks experience changes in their basic structure depending on the process stage. Initially, hydrocolloids can contribute to proper mixing and forming of the dough by viscosity control. During extrusion, the dough forms a foam which is rapidly desiccated to a film structure.  "In a cereal, crunchiness and flakiness are important," says Ward. "I recommend gums that dry to form very brittle gels."  Adds National Starch's Izzo: "Integrating a high-amylose starch into a cereal or snack helps control expansion out of the extruder. Amylose actually has the ability to align and form a more continuous matrix in the cereal piece and to decrease the tendency of water to penetrate. This enhances the bowl life of the cereal."  Confections also make use of multiple basic structures. For the most part, candies start as a viscous liquid which is then cooked down to a gel structure or even a film.  Marshmallows combine the basic structure of a gelled foam with a soft, elastic texture contributed by gelatin. Marshmallows begin as a viscous liquid structure which is cooked and aerated. Unfortunately, gelatin thins at higher temperatures, making it difficult to achieve the right foam during this process. Adding a starch provides the necessary viscosity for proper aeration. This added body helps at the cutting stage of the process because the marshmallows won't tend to collapse and form "pillows."  Many confections have extremely limited moisture levels. This combined with the high sugar concentration can make the use of a hydrocolloid challenging because the competition for the available water can cause phase separations. In gummy bears, for example, a phase separation would cause the product to be unexpectedly soft.  "The molecular weight distribution of corn syrup can have a significant effect on how a gelatin works in a gummy bear," says SBI's Carr. "If the molecular weight of the corn syrup is too high, you can phase-separate out the gelatin. You see very different behaviors in a water-limited system with which you must be more cautious."  Whether it's a confection, baked product or snack, any limited-moisture system requires special attention to hydrocolloid incorporation because the moisture is so critical to hydrocolloid function.  "Whether those solids be from a high sugar content, a high cocoa content or a high grain content, the limitation will be that you have a moisture phase disrupted by a high solids content," says FMC's Bullens. "That's going to directly affect how well the aqueous phase can bind those ingredients together."  Last are the intermediate- and high-moisture solid foods, which include processed meats, analogs and some processed cheeses. Here, the basic structure is a gel and the hydrocolloid often has a direct influence on the final product's firmness of bite. The starch or gum's water-holding properties also contribute to the product's juiciness.  The amount of juiciness and the firmness of bite dictate the type of hydrocolloid selected - whether it is gelling or non-gelling, and the degree to which it binds moisture.  "You also have to select the hydrocolloid with a texture that is more natural for the product," says Carr. "Here, you're actually talking about establishing a gel network that provides a cohesive texture. The gel must have a certain cohesive quality, and it must have a texture similar to that of the type of meat product you're trying to enhance."  Related to meat products is the use of film-forming hydrocolloids in batters and breedings. In these applications, the hydrocolloid helps the batter or breading stick more uniformly to the product and it can help reduce oil pickup in the fryers.Getting under construction  Since building the desired texture into food products requires a proper blueprint, the first step is to determine and define the product's desired texture.  "The food scientist has to have an understanding of the type of texture they're looking for - whether it is smooth or rough, elastic or brittle, or soft or firm," says Rhône Poulenc's Freeland. "Then we have to have an understanding of what textures can be obtained with hydrocolloids and mixtures of hydrocolloids. Many of these mixtures are synergistic, and other combinations may create a texture that is very different from either individually."  It helps to characterize the desired texture rheologically. Even if it isn't an exact match for the target, at least the designer has an objective starting point to use as a developmental target. From here, you can always redefine the texture as being softer, stronger, needing more moisture, and so on. Of course, some textural features defy any method besides sensory description, namely the degree of mouthfeel and how fast it dissipates.  The way the product will be used also is important. Dry mixes for soups, marinades and gravies won't build their final texture until prepared by the consumer. This requires special attention by the designer to create a hydrocolloid system that will build the desired texture under less-than-ideal conditions.  "In a hot cocoa mix, the consumer adds hot water to the system and begins drinking it within 60 seconds or less," says Freeland. "You need the mouthfeel and stability to be ready within that 60 seconds."  With your goal in mind, you can begin selection and incorporation of the appropriate hydrocolloid. Just as the previous stage defined the requirements of the hydrocolloid system, this stage starts by establishing the limitations of the product under development.  "The first thing you have to nail down is what you want and if you have any cost restrictions," says Dan Lis, a carbohydrate scientist with Glenview, IL-based Kraft General Foods. "Starches are usually significantly less expensive than other hydrocolloids."  Related to cost is the need to check out the existing hydrocolloid ingredients if the project is a reformulation. If the product is well established, designers on previous reformulation projects may have added hydrocolloids to the formula. Over the years, these incremental formula changes can result in a hydrocolloid system that is much too complex and expensive. Avoid complicating the problem by stripping the hydrocolloid system and only adding back what's necessary.  Next, make sure the product will comply with regulations. In particular, the standards of identity for certain products may limit the hydrocolloid choices available. This is doubly important for products created for export because every country's regulations differ. In these cases, though, regulations aren't the only limitation to consider.  "In Europe and Japan, the regulations and cultures are both very different," says Bullens. "Culturally, certain ingredients aren't as readily accepted by consumers in other countries. You have to be familiar with both the regulatory and the societal acceptance criteria for where the food product is going to be consumed."  An example of such criteria can be seen in the "clean label" and "natural" requirements commonly found in the United States but not everywhere else.Building on the foundation  At this stage of the project, the field of potential hydrocolloids will have been pared down significantly. Still, a good deal of formulation and testing lies ahead. One way to make this more efficient is to examine the product and establish its basic structure. With the basic structure in mind, the designer will have a clearer idea of the functional properties required of the hydrocolloids to be used. If the basic structure involves a gel, you'll know you need a gel former. If the structure requires a film, you can focus on film formers. Remember, though, this isn't limited to single ingredients.  "You also have to know about incompatibilities and synergism," says TIC's Ward. "Locust bean gum and xanthan gum will form a beautiful gel together, but not alone."  Understanding the basic structure helps show the amount of viscosity/stabilization required. This will guide selection of the functional strength of the hydrocolloid and begin the process of establishing an appropriate usage level.  "Try to visualize the rheological characteristics on a continuum going all the way from a fluid viscosity to a solid structure," says Bullens. "Then select gums and starches that can provide the structure on the point of that continuum that matches the product requirements."  Remember to look at combinations. Not only do combinations form different structures than individual hydrocolloids, but many offer increased functionality at a lower (and less expensive) usage rate.  "Two hydrocolloids might be synergistic, or they simply can compete for water for a more complementary relationship," says Bullens. "You also may want to apply antagonistic relationships between two ingredients in order to get a desired intermediate texture.  Knowing the basic structure also helps the designer create a model system for experimentation and rheological testing. This can be a great time saver when evaluating texture and establishing a starting use level range.  "I usually try to extract the fundamental components and create a model system that leaves out flavor, color and, to a certain extent, preservatives," suggests Bullens. "I end up with something I can put together in a fairly large volume with which I can do a number of replicate tests."  Such an approach saves time because the designer won't have to spend so much time weighing small batches. A portion of the large batch can be used to test different ingredients at different levels. This gives the designer a better feel for the rheological characteristics of the system and the levels of gums and starches that will come close to the target qualities.  At the end of model system experimentation, product designers should be able to narrow the ingredient field down to the two or three best alternatives. These should then be incorporated into the complete formula, where the use levels will be fine-tuned and the results confirmed by rheological testing and sensory evaluation.  When the project reaches the stage where the designer is working with the entire formula, it's also time to consider potential production and distribution limitations more carefully. In the lab, almost anything is possible. Scale-up can be a different story, and ingredients might have to be adjusted to get the desired texture and flow properties.  "Sometimes you can't use certain ingredients in the plant," says Freeland. "It may have been designed only to do certain things and can't handle some ingredients."  Remember, too, that once texture is established it doesn't necessarily mean that the texture will be maintained over the shelf life of the product. Determining how well the hydrocolloid system holds up should include long-term shelf life studies and distribution tests.  Focusing on a product's basic structure helps sift through the many potential hydrocolloids for building texture. Although it may seem like a lot of effort, a day or two of examination and planning might save weeks of trial-and-error ingredient testing. Considering that product designers are facing intensifying quality demands from consumers while project timetables seem to be imploding, such an approach is more than a nice idea, it's a necessity.Back to top