In the Thick of It

May 2005

In the Thick of It

By Cindy HazenContributing Editor

When it comes to improving texture and adding body to foods, home cooks have a few well-known tricks. Flour, corn starch or arrowroot, mixed with cold water and added to sauces or gravies, will provide thickening. Heating these ensures a less-starchy flavor. A browned butter-and-flour mixture provides a sauce base (roux) to which liquids can be added, or equal parts butter and flour, kneaded together (beurre manié), can be added at the last minute to increase viscosity. Pectin in jams and jellies gels when heated. All of these take advantage of the thickening qualities of carbohydrates.

While these tried-and-true pantry staples satisfy the needs of most cooks and chefs preparing food for relatively quick consumption, the food scientist develops products that people might not consume for days, weeks or even months. They might be rehydrated and microwaved, stove-cooked, oven-baked or frozen through countless temperature cycles. As if that isn't challenge enough, consider removing half of the inherent fat or carbohydrates with a mandate to maintain the textural properties of the original. Thankfully, the lab has an arsenal of carbohydrate-based tools not available in the average kitchen.

Carbs through thick and thin On the shelves marked "starches" and "gums" lies a spectrum of carbohydrates called polysaccharides that possess different functions and attributes. However, selecting the right product is not that easy. Where do you begin? With the application, says Susan Gurkin, applications service center director, NAFTA, Degussa Texturant Systems, Atlanta. "There's a wide range of different hydrocolloid gum options that you can choose to get clear gels, for example," she says. "It depends on the specific end properties and some of your processing limitations." For example, some products require cold-water solubility, while others will be cooked.

"A starch granule requires energy input in the form of heat to open the molecular structure and initiate hydration (sometimes referred to as gelatinization)," says Celeste Sullivan, senior applications scientist, Grain Processing Corporation (GPC), Muscatine, IA. "There are also pregelatinized or instant forms available where the hydration has been done by the manufacturer. Many conditions and ingredients may affect that hydration. Chemical modifications might initiate hydration at low temperature while other modifications can delay the onset of hydration and viscosity development until higher temperatures are reached. Solids, such as sugars, salts, fats, hydrocolloids and gums, may compete for available moisture when cooking starch or coat the starch granules impacting hydration."

Not all hydrocolloids performs alike, and this makes the world of gums very complex, says Karen Laustsen, R&D director, Ceamsa, Spain, a company represented by P.L. Thomas, Morristown, NJ, in North America. "The food matrix, as well as the processing conditions during food preparation, have major influence on the final performance of the individual hydrocolloid," she notes. "pH, availability of gelling salts, synergies between gums and proteins, and shear and temperature during holding time during processing are all important factors."

Processing is a critical consideration. "When you look at convenience foods for today, you're looking for the variety of reconstitution -- be it steam table, microwave, conventional oven, stove top," says Tom Luallen, assistant vice president, technical director, Cargill Food & Pharma Specialties, Minneapolis. The freezer adds even more stress.

Carbohydrate hydrocolloids all provide some thickening -- but not all in the same way. "Guar gum, CMC (carboxymethylcellulose) and lambda carrageenan function as thickeners by hydration," says Laustsen. "Kappa and iota carrageenan acts as proper gelling agents." She notes that kappa carrageenan forms a very strong network while iota carrageenan makes an elastic, thixotropic (shear thinning) gel. "HM pectin gels at high solids, but only if pH is low," she continues. "LMA pectin or alginates, on the other hand, gel with calcium ions -- just to mention a few examples."

According to Paul Flowerman, president, P.L. Thomas: "Xanthan-guar combinations give very efficient swelling results. There are different kinds of molecular bonding involved in increasing viscosity, swelling and loose gel formation. Guar and locust bean gum and lambda carrageenan do not form networked gels, but add some xanthan to locust bean gum, or use kappa or iota carrageenan, and, certainly, a gel matrix may gradually form."

We've moved beyond plain, old kitchen corn starch, too. "Native starches can be used for thickening, as aids for sugar grinding and as a dusting agent," says Michelle Kozora, food scientist, technical services, Tate & Lyle, Decatur, IL. "However, native starches are not able to hold up to processing conditions such as freeze/thaw, high heat treatment, high acid or high shear. So native starches are chemically modified in order to survive these conditions." Base starches, such as corn, potato, tapioca, and wheat, can be chemically and/or physically modified.

Chemical modifications include dextrinization, oxidation, thinning, substitution and crosslinking. "The two main chemical modifications are substitution and crosslinking," says Kozora. "When a native starch is chemically modified by substitution, the starch gains more water-holding capacity. This allows the starch to be able to survive several freeze/thaw cycles and still maintain water-holding. Also, because the starch can hold more water, the peak viscosity is increased."

The two water-holding substitution methods are acetylation and hydroxypropylation. "The reagents used in each are different and will give slightly different water-holding capabilities," says Kozora. "Acetylation is the first generation and gives better water control over native starches. Hydroxypropylation is the next generation and gives better water control over acetylated starches. A third method of substitution involves fat and/or oil control. Starches are lipophilically substituted to control oil in products like high-fat sauces. These starches are called lipophilic or octenyl succinated (OS) starches."

Functional differences exist between native starches. "Many tuber and root starches, such as potato and tapioca, are larger than seed starches, such as corn," says Sullivan. "They generally are less dense, having weaker intermolecular bonding, and are easier to cook-out. They tend to be less shear tolerant and the highly swollen granules break easily. Rice and wheat starches are tiny granules and produce lower viscosities. The amount of amylose present may also impact that swelling capacity, the higher-amylose starches being very difficult to cook-out."

Unmodified native starches usually aren't appropriate for processed applications. "Native starch granules do not exhibit any stability required for most processed-food applications today," says Sullivan. "Upon heating, the starch granules exhibit swelling by combining with water molecules, thickening to form a paste. This allows for suspension of other ingredients or particulates. Upon cooling or holding, the paste may congeal to form a semisolid gel. Over time, syneresis often occurs. This is an undesirable result of this gelling. The bound moisture is released. Although inexpensive to use, unmodified starch granules do not exhibit acid, heat, shear or freeze-thaw stability, requirements of the food manufacturer. They also form opaque gels."

Sullivan notes that combined modification techniques can yield unique ingredients. "Many starch manufacturers today use a combination of both crosslinking and substitution to produce ingredients that will yield the maximum processing stability for the customer," she says. "Selection of an ingredient for an application is based on the final product demands from concept to consumer. The selection and performance depend on other ingredients used in the formula, targeted product attributes, processing conditions and the distribution, storage and handling demands."

When a native starch is chemically modified by crosslinking, it gains strength. The goal is to keep the starch granule intact. "When a starch granule is overprocessed -- by either too much heat, too much acid, and/or too much shear -- the granule will break and cause unappealing attributes to a product," says Kozora. "These attributes include a slimy texture and a loss in viscosity. Crosslinks are chemically added to the starch molecule. As a result, the starch is able to withstand high heat, high acid and/or high shear." A crosslinked starch does not gain as much viscosity as a native starch because it is restricted from swelling -- it won't provide as much viscosity as native starch.

Starches can be physically modified to instantize and/or agglomerate the product -- to allow them to swell instantly without cooking. According to Kozora, starches are instantized in one of two ways: precooking and drying (typically a drum dryer) for pregelatinized instant starches and preswelling and drying for granular instant starches. "Due to the cooking method, pregelatinized instant starches have few intact granules and granules with jagged edges," she says. "Granular instant starches have all-intact granules and granules with smooth surfaces. The shape of the granule will affect the finished product. For example, a pregelatinized instant starch will give a grainy appearance to a pie filling where as a granular instant starch will give a smooth, shiny appearance."

Through hot and cold It's important that developers ask the right questions. "Are they looking at a product that is really to be frozen and thawed a number of cycles," Luallen asks, "or are they looking at a product that is to withstand extended freezing?" While product designers can add many ingredients to provide stability through four, six or eight freeze/thaw cycles, he points out that not all ingredient combinations can give three months, six months or nine months of continuous freezing capability, because many food systems don't totally freeze due to high levels of solids or salts. For, example, ice cream is not totally frozen -- water can migrate from one phase to another. "Water management and ice-crystal development are critical in maintaining freeze/thaw stability and extended freezer stability," he says.

Though some products, like pizza, turn over on a frequent basis, it's more typical to see products with 9- to 15-month freezer requirements that go through various cycling temperatures, causing moisture migration from one phase of the food to another. At that point, it's critical to limit moisture migration to retard damaging ice-crystal formation. Moisture migration can occur at temperatures as high as -40?F.

For stability, modified starches work best. "Ideally, you're looking at monosubstituted, crosslinked starches that can be based on various starch systems," Luallen says. "You can use common corn, waxy maize, tapioca, potato, wheat -- and each one, if modified appropriately utilizing monosubstituting and crosslinking, will provide certain freeze/thaw and freezer stability. However, they do vary based upon the food system, the processing and then the texture and longevity of stability that you're looking for. I have worked with, and found that if I'm looking for, extreme freeze/thaw, a modified waxy maize works extremely well, depending upon the longevity of the shelf life. If it's less than six months, you can use common corn. If you're looking for greater than that, you should really look at other starch systems, such as waxy maize or tapioca. In Europe, they also use modified potato for freezing and freeze/thaw stability."

For products frozen for long periods, a blend of modified starch and xanthan gum can provide the best result. Xanthan provides reduced textural changes upon reconstitution. Very low levels provide excellent water binding or water management because it works synergistically with modified starch in most food systems at low levels better than some of the other gums.

Xanthan gum is the ingredient of choice in many food applications for many reasons. "It has high functionality at low use levels, a wide pH range for stability (wider than other similar ingredients) and excellent enzyme/salt/shear/ temperature stability," says Yvonne M. Stuchell, senior research food scientist, specialty food ingredients, ADM, Decatur, IL. "It is easy to use and has wide approval in food system."

Don't forget to consider the application. "It's going to be different if you're doing a frozen dough versus a sauce or dressing," Gurkin says. "You have to consider the stress of the initial processing versus what the desired finished texture will be." While she notes that xanthan is the workhorse in that industry, she finds that some applications require alternatives. Compounding xanthan and guar will give a slightly different texture. "What the guar does, is during part of the freeze/ thaw, it mops up a little bit of the water," she says. "The same can be said for alginate/pectin blends." This gives a wide range of options for a finished product category.

"Many gums can control ice-crystal growth and provide freeze/thaw stability, thanks to their ability to bind water," says Greg Andon, business development manager, TIC Gums, Belcamp, MD. "The choice of gum system depends more on the processing requirements and the other ingredients in the product. A low-pH formulation will require a different gum than one with a neutral pH. Many times, a gum system (blend) delivers the best stabilizing solution. For example, xanthan gum is very tolerant to acidic pH levels, but high concentrations of xanthan can create a texture that is characterized as 'gloppy' or 'snotty.' By using a system of both xanthan and gum arabic, you can achieve thickening with a smooth texture."

When adding hydrocolloids to frozen foods, consider the contribution of other ingredients. Some sweetener systems tend to act as moisture-control agents. Adding monosaccharides like fructose and large-molecular sweeteners, such as maltodextrins, can enhance moisture control and reduce crystal formation and damage. "When you put together a food system, it's just not the starch or the gum that you're putting in there," Luallen says. "It is the interaction and synergy of the thickener, such as the starch or the gum, in combination with the sweetener system, in combination with the salt system. It's a balanced system."

Hydration considerations also affect a gum's performance. "The hydration rate of gums is affected by temperature, soluble solids, presence of gelling salts, etc.," says Flowerman. "Poor gum hydration will result in poor texturizing performance, and thereby reduced cost effectiveness. Lump formation and obstructions of filters also can be problematic."

Mouthfeel modification Mouthfeel encompasses texture, flavor and flavor delivery. Custards, cream fillings, sauces and gravies are prized for smoothness. Any perception of graininess usually detracts. Not only is a clean flavor essential, but the way that flavor disperses in the mouth is critical to the product's success. Some applications require a very clean delivery, while other products are improved when the tongue is lightly coated. Likewise, the sensation of flavor should be pleasant and not dissipate too fast.

A correlation exists between mouthfeel and rate of hydration, not only from the water used in processing, but also from enzymatic degradation in the mouth. Rapid hydration can improve mouthfeel and provide creamy texture. "But you don't want it to degrade too fast," Luallen cautions, "otherwise, you lose mouthfeel and 'chewability.'"

Deborah Dihel, Ph.D., product innovation manager, National Starch Food Innovation, Bridgewater, NJ, explains: "In its swollen granular state, starch can provide firmness, 'mouthcoating,' cohesiveness and body to high-moisture, semisolid food products like sauces and yogurts. In lower-viscosity, liquid foods like beverages, certain starches, such as a modified tapioca, can be used in a fully dispersed polymeric state to add cling, lubricity, creaminess and 'mouthcoating.' In low-moisture foods, film-forming starches can be used to improve crispiness and crunchiness in fried foods, or alternatively hold water and provide moistness in products like nutrition bars and baked goods."

The state of the starch polymer (granular or dispersed), the base source, modification, processing method and other ingredients contribute to the product's texture. "The understanding of these variations, as well as their impact on the sensory response, is vital to the development of preferred food products," Dihel continues.

Basic starch chemistry, the ratios of amylose and amylopectin, greatly impact texture. "Amylose is a linear polymer that, once cooked, can leach from the starch granule," Dihel explains. "Leached amylose polymers can reassociate into aggregates and precipitate at low concentrations, or set to a gel at higher starch concentrations." This is referred to as "setback" or "retrogradation." Because amylopectin is branched, it does not reassociate as readily, and provides a more-stable, flowable texture. "Starches made from dent corn or high-amylose corn are used in filming or gelling applications due to their naturally higher amylose contents," she says. "Waxy maize, which contains high levels of amylopectin, is used when a set or gel is not desired and a flowable, creamy texture is preferred."

Amylose and amylopectin differ in structure and characteristics, and therefore have distinct effects on formulations. "Amylose and amylopectin are long-chain polymers of repeating anhydroglucose units within the starch molecule," says Sullivan. "In most starches, the alpha-1,4 linkage is predominant. These alpha-1,4 linkages yield straight-chain molecules known as amylose. The alpha-1,6 linkages serve as a branch point and are referred to as amylopectin. The proportions of these are genetically established and are relatively consistent for each starch species. In its native or unmodified form, amylose tends to produce a more-rigid structure or gel while the amylopectin tends to produce a softer, nongelling structure or paste. Unmodified amylopectin texture is long and snotty."

Starches and gums work well together and are most-often used in combination. "Starches will provide viscosity and can provide more of a set texture," explains Kozora. "Gums, such as xanthan gum, also provide viscosity but will also provide a longer texture than starch can sometimes give. In pourable salad dressings, for example, both modified starch and xanthan gum are typically used in combination. The modified starch aids in the viscosity and gives smoothness and shininess to the dressing; the xanthan helps to give the longer texture desired in a pourable dressing."

Gum selection can greatly impact mouthfeel, and a wide range of carrageenans is available. Gurkin cautions that among the thickening carrageenans, textures range from what she describes as "hockey puck," rubbery gels to watery gels.

"From carrageen, you can get anything ranging from a very clean mouthfeel to something that will linger in the mouth a little bit longer and coat the tongue," says Donna Pechillo, senior research scientist, FMC BioPolymer, Princeton, NJ. Carrageenan is extracted from red seaweed and categorized into three types: kappa, iota and lambda. Kappa carrageenan will provide the least "mouthcoating," while iota or lambda carrageenan can impart a coating effect as desired.

"They have varying anhydro-galactose (AG) units and ester sulfate groups," Pechillo continues. "The amount of both AG and ester sulfate groups will determine how hot/cold soluble the products will be. In general, the higher the 3,6 AG units and the lower the ester sulfate groups, the less cold-soluble the carrageenan will be in water. All carrageenan types will swell/hydrate in cold water, but not all will completely solubilize." Lambda carrageenan is the most cold soluble, and the kappa is the least cold soluble, in water. Iota is somewhere between the two.

Each molecular form causes a different mouthfeel. "Carrageenan is a great gelling agent for shelf-stable water gel desserts, with the advantages of being approved for vegan and kosher products," says Aida Prenzno, vice president of R&D, Gum Technology Corporation, Tucson, AZ. "Konjac gum can form a nonthermoreversible gel with a fatty mouthfeel that can be used to reduce fat in meat applications." She also notes that sodium alginate is essential in some restructured products, such as onion rings and pimento pieces for stuffed olives.

"All alginate products based upon brown seaweed are cold soluble," Pechillo explains. "They also have different degrees of mannuronate and guluronate units, which will determine whether or not they are used for viscosity or gelling purposes. Alginates will gel in the presence of calcium at room temperature." The application and the way the product designer uses calcium in the formula -- how it is sequestered or if it is overloaded -- will determine the type of gelling, from firm and brittle to soft and flexible. Similarly, it will impart a clean flavor release with a light or heavy coating in the mouth. Alginates can thicken-up sauces and gravies or create bake-stable fruit or neutral-type fillings.

Propylene glycol alginate, which is also cold soluble, can suspend ingredients, thicken systems and modify mucilaginous textures, especially in salad dressings. "It is used with other gums to create a shorter type of texture," Pechillo explains. "We do the same thing with microcrystalline cellulose (MCC), or even carrageenan, to break up the structure and improve the texture of the finished product. The MCC is used in conjunction with starch to shorten the texture, without making it pasty or gummy, with a clean flavor release."

Andon notes: "Increasing the viscosity of a solution will increase the mouthfeel when consumed. Mouthfeel, however, is not viscosity alone. The same viscosity can be achieved with many different gums with very different textures. Gum acacia, otherwise known as gum arabic, offers very little viscosity at low concentrations. This makes it a great choice for beverages where a slight increase in smooth mouthfeel is desired. Gum arabic also works well to modify the texture of other gums, such as xanthan."

Likewise, adding other gums to the formula can alter agar's gelling properties. "It provides a brittle gel when used by itself," Andon says. "The addition of other gums, in an agar-based system, such as locust bean gum, carrageenan and xanthan can provide a more-elastic characteristic to the gel. Locust bean gum provides a smooth, creamy texture in a variety of applications, including dairy-based products. It's a good choice for culinary sauces to replace more-traditional thickening tools, such as roux or starch, either by itself or in combination with a bland-tasting guar gum."

Other gum combinations can also make for some interesting synergies. "Xanthan gum has become a workhorse, not just because of what it can achieve by itself, but also because of its synergistic capabilities when used with other hydrocolloids," says Prenzno. "For example, when a blend of xanthan and guar gum is added as a thickener agent, the amount of gums that you'll need in your formula is almost two times less" than xanthan alone.

Xanthan gum also reacts synergistically with locust bean gun to produce very soft and elastics gels. Prenzno also notes that adding locust bean gum to carrageenan produces "more-elastic gels that are less prone to syneresis than those containing carrageenan alone. These ingredients are widely used in water gel desserts and pudding-type products."

Starches and gums work well together -- most often in combination. Starches provide viscosity and can give more of a set texture, according to Kozora. Gums, such as xanthan, lend viscosity but also can provide a longer texture than starch. "In pourable salad dressings, for example, both modified starch and xanthan gum are typically used in combination," notes Kozora. "The modified starch aids in the viscosity and gives smoothness and shininess to the dressing; the xanthan helps to give the longer texture desired in a pourable dressing."

The director's cut It's important for the food developer to keep a sharp focus on the desired end product while staying aware of every processing step along the way. Sometimes, hydrocolloids can even help lessen the impact of these bumps. "Hydrocolloids, for example, MCC, will improve processing throughput by reducing in-process viscosity through the reduction/replacement of other gums in your system," Pechillo says. By imparting shear on a system, MCC improves throughput because it is thixotropic. "Your product will heat-up faster and actually process through your equipment quicker," she says.

Agglomerated gums are easy to work with. "There is virtually no lumping, even when gums are added to cold water with little agitation, and they handle with little dust," Andon says. "Most gums and gum systems can be processed to become prehydrated, and we work with customers to agglomerate their custom blends."

Starches, too, can be agglomerated to increase ease of use. "Basically, the surface of an instant starch granule is wetted, which causes several granules to stick together," says Kozora. "As they are stuck together, air pockets are created and a larger surface area is created. This allows the starch to go into solution without any diluents. The water rushes into the air pockets, and then allows the starch to hydrate."

The key to maximizing ingredient benefits is to work with the supplier from the outset. It's important for that supplier to ask questions. How much shear exists in the process? Any heat? Acidic conditions? Any label claims? Lastly, it's important to consider synergies of other hydrocolloids or ion-containing ingredients, such as calcium, potassium or sodium.

"It's a fairly complicated matrix that you're trying to put together, dependent upon the food system that you're trying to deliver to the consumer, or to an individual that might be evaluating the product," Luallen says. "It gets quite complicated, but it makes our job fun."  

Cindy Hazen, a 20-year veteran of the food industry, is a freelance writer based in Memphis, TN. She can be reached at [email protected].

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