Food Product Design: Applications - August 2005 - Maintaining Texture

August 2005

Maintaining Texture

By Karen GrenusContributing Editor

Maintaining texture in foods is all about shelf life. Processed foods can sit for months before they hit a consumer's palate. What's more, product designers need to not only choose ingredients that deliver the target texture -- and maintain it through processing, shipping and storage -- but those that keep the correct viscosity, suspension and flowability to avoid problems in the production line.

In foodservice, some elements can be prepped hours ahead of time. From the dipping sauce for the appetizer to the cake for dessert, each food's texture needs to meet consumers' expectation, regardless of holding time. Holding food at serving temperature for hours makes formulation critical in maintaining product rheology.

Maintaining food texture is a tall order when up against the laws of nature. Formulations need to be crafted to slow the effects of moisture equilibration and loss, and counteract other thermodynamically favored reactions such as crystallization and coalescing. Fortunately, tools exist to delay the inevitable long enough to deliver an appealing product over a reasonable shelf life.

Holding it together In an emulsion, dispersed-phase droplets that contact each other want to coalesce, or form a larger droplet, to reduce the area of the interface. Two ways to prevent this are making droplet surfaces less attractive and increasing the viscosity of the continuous phase to limit droplet movement. "Part of the molecule of the emulsifier will stick into the oil droplet, and part of it will hang out in the water. It sort of shields the oil droplet from finding another oil droplet and coalescing," explains Erin Chavez Surratt, senior application specialist, Degussa Texturant Systems, Atlanta.

Emulsifiers are described by their hydrophilic-lipophilic balance (HLB), which measures solubility in water versus oil. Formulators need to consider the emulsifiers' solubility in water and oil as a function of temperature, as described by the phase-inversion temperature (PIT). Some emulsifiers, such as sodium stearoyl lactylate (SSL), are ionic and the charge will temper the attraction between oil droplets in an oil-in-water emulsion.

"When creating an oil-in-water emulsion, it is best to choose an emulsifier on the high end of the HLB scale -- 8 to18 -- as opposed to a water-in-oil emulsion requiring an emulsifier with a lower HLB -- 3 to 6," says Chavez Surratt. "The HLB scale is a nice tool, but remember not all emulsifiers fit nicely onto this scale and ionic ingredients such as lecithin, although it has an HLB above 9, can be modified to function in either oil-in-water or water-in-oil emulsions."

Emulsifiers can function beyond stabilizing emulsions. Distilled monoglycerides, SSL and calcium stearoyl lactylate (CSL) can complex with starch, which plays an important role in bakery applications.

Polyol performance Polyols, sometimes called sugar alcohols, cover a wide range of solubility and sweetness, and are also differentiated by properties such as calorie content and cooling effect. In reduced-sugar or low-carbohydrate applications, they find use as reduced-calorie sweeteners and bulking agents. Several polyols make excellent humectants, a characteristic that can control texture.

"Sorbitol and mannitol have been around since the 1930s. Sorbitol was a byproduct of mannitol production, which was used in controlling the stability of dynamite," says Peter Jamieson, manager of applications, research and technical services, SPI Polyols, Inc., New Castle, DE. "There's a big assumption that all the polyols are the same, but they are not. They all have their advantages, and you as the formulator needs to understand the physical properties of each and how it's going to benefit your application," says Jamieson. For example, sorbitol has a solubility of 235 grams per 100 grams of water at 25?C, while mannitol has the same molecular weight but has one-tenth of the solubility. Because it's less soluble, it also is much less effective as a humectant. Like sugar, maltitol is a disaccharide and can be used as a 1:1 replacement.

"Often overlooked is the cooling effect that polyols have. A lot of people don't realize its significance and impact on an application," says Jamieson. The cooling results from a negative heat of solution; the more negative the heat of solution, the greater the cooling effect. Sorbitol has a heat of solution of -26.5 kcal per gram, compared to sucrose's -4.3 kcal per gram. He offers that ingredients with a positive heat of solution, such as inulin, can offset polyols' negative heat of solution.

Success with polysaccharides "Gums improve moisture retention, which in turn results in an extension of product shelf life," says Maureen Akins, food scientist, TIC Gums, Belcamp, MD. "This is evident in the use of gums in bakery products. Gums can limit the amount of ice-crystal regrowth in frozen foods. This prevents further damage to fragile cell walls, or incorporated air such as found in ice cream. Gums provide emulsification necessary for product stability in products such as beverage emulsions and salad dressings. Proper stabilization will allow for extended shelf life, create more visually appealing products and creamier mouthfeel."

Hydrocolloids impact product texture through their relationship with water. "Hydrocolloids are water-soluble macromolecules with high molecular weight consisting of hydrophilic long chains," says Aida Prenzno, vice president R&D, Gum Technology Corporation, Tucson, AZ. "They change the rheological properties of the aqueous systems to which they are added. They can increase the viscosity or form a network of molecules to provide a gel texture."

In water-limited systems, hydrocolloids reduce moisture loss or migration by lowering water's mobility. "Because gums are efficient water binders, they are able to control the movement of water that occurs during freeze/thaw cycling of frozen foods," says Akins. "This prevents water from accumulating and forming large ice crystals in the product. This can also be compared to staling in bread, where dehydration contributes to starch retrogradation. The ability of gums to delay this loss in moisture helps to increase shelf life."

The many gums and blended products create an infinite array of possible solutions to any texture challenge. Galactomannans, such as guar gum and locust bean gum, offer high levels of water-binding and viscosity. Guar gum is cold-water-soluble and very economic to use, while locust bean gum needs heating to function. Locust bean gum is widely used where creamy mouthfeel is important.

Xanthan gum is the gold standard in terms of acid stability and exhibits the property of yield stress that makes it desirable in pourable dressings. However, xanthan is not well suited for all applications, according to Chavez Surratt. "Xanthan gum has an interaction with proteins," she notes. "This interaction can lead to precipitation, and can lead to a very grainy texture. You don't see large dosage of xanthan gum used in products containing high protein and high acid."

Carboxymethylcellulose (CMC) is popular for applications in the pH range of 4 to 10. It imparts "excellent clarity and rheological properties to syrups, sauces and soups," says Akins. CMC's solubility is reduced in the presence of divalent cations, such as calcium, and precipitation can occur in the presence of trivalent cations. Pectin is acid-resistant and can form strong gels in the presence of acid and sugar. Low-methoxy pectin is stable over a wide pH range and can gel without sugar. As a viscosifier or gelling agent, pectin is usually heated to hasten its functionality.

Carrageenan is a family of hydrocolloids extracted from seaweed. There are at least five carrageenan polymers, and three -- lambda, kappa and iota -- are used in food applications. "The interaction that carrageenan and casein molecules have is actually a synergy to increase the properties of the carrageenan. If you add dairy proteins -- casein -- to carrageenan, you will have higher gel strength or higher viscosity than if you are just viscosifying with the carrageenan. Because of their molecular structure, kappa-type carrageenan molecules tend to react to casein molecules a little stronger than an iota-type carrageenan would. Lambda carrageenan only provides viscosity," says Chavez Surratt.

Xanthan and guar blends can produce higher viscosity than either alone, and provide higher acid tolerance than the guar would by itself. Chavez Surratt adds that xanthan and locust bean gum will form a gel that could be used at a low level in some fluid applications, and locust bean gum will increase the firmness of a carrageenan gel, as well as help maintain the ability to hold water.

Process and sequencing are important for the full functionality of hydrocolloids. Those that require heat, such as locust bean gum, agar and some forms of carrageenan, must be cooked completely to maximize their properties. Except for specialty products, gums must be dispersed in oil or dry ingredients to separate the particles to prevent clumping and achieve full hydration. "It is important to know all the environmental conditions of the product before selecting your hydrocolloid," advises Akins. "The amount of available water, pH conditions, competing solutes such as sugar or salt, and availability of heat or shear will all play a role in the success of hydrocolloids in your product. If the gum can't get activated, it isn't going to be effective."

The properties of starch depend on the source of the starch and chemical and mechanical modifications. The two polymers that make up starch are amylose and amylopectin. The highly branched amylopectin creates viscosity when it is cooked, whereas linear amylose will tend to gel or form crystalline regions. The ratio of amylose to amylopectin varies with the starch source, as does the starch-granule size and pasting characteristics. Chemical or mechanical modification of the molecules can alter the starch properties and create products more suited to specific environments, such as specific pH levels, as well as processing conditions like freezing or high shear.

Better bakery applications Although the exact mechanism of bread staling is still under discussion, the effects are well known. "Bread staling is a number of things," says R. Carl Hoseney, president, R&R Research Services Inc., Manhattan, KS. "We normally measure it by the increase in firmness, but we know that the product can become more crumbly, lose flavor and lose mouthfeel. Most predominant is that the bread gets firmer to the touch," he says. Lean formulation and low moisture or the loss of moisture are factors in more-rapid staling.

Temperature can also impact   the staling rate. According to Hoseney, staling is accelerated at refrigerated temperatures, halted at freezing temperatures and can be reversed through heating processes. "You want to heat it without driving moisture off, which of course is not easy to do," he says. "The best way to do it is with intense heat where the time isn't too long, and that's what your toaster does."

Freezing baked goods also leaves them susceptible to staling. "Frozen products can be particularly challenging, as the low humidity and freeze/thaw cycles encountered can damage product integrity," says David Kappelman, technical manager, bakery, Danisco USA, Inc., New Century, KS. "Staling occurs most rapidly at around 50?F, so fully baked, frozen products need to be chilled as rapidly as possible to avoid this temperature range for extended periods of time."

Crystallization and moisture loss are two primary causes of staling. "Starch crystallization can be controlled by two mechanisms," says Neil Widlak, director, business and product development, ADM, Decatur, IL. "One is by providing ingredients that will interfere with starch crystallization, or retrogradation. Typically used are crumb softeners, like distilled monoglycerides, SSL and CSL. Those are crystallization-retarding or -interfering types of agents. The other method to limit starch crystallizing is by using enzymes that break up the starch molecule, reducing the size of the starch molecules and their impact on hardening." The Code of Federal Regulations limits levels of distilled monoglycerides, SSL and CSL to 0.5 parts per 100 parts flour in baked goods.

Enzymes have a more long-term effect, whereas the effect of emulsifiers can be seen upon cooling. Emulsifiers interact with starch after the starch gelatinizes as the bread dough is baked. "As the bread cools, it starts to crystallize, and that is the exact same time that the emulsifiers and crumb softeners start to take effect," Widlak notes. Enzymes are active as soon as they hit the dough, so any unexpected process stoppage prior to baking might affect finished product quality. Manufacturers add enzymes dispersed in a carrier or in tablet form for consistent delivery due to the small amount, usually ppm, in the formula.

Moisture control, and moisture perception, is obtained through the use of fats, hydrocolloids and humectants. Fats not only impact staling, but also give the perception of moistness. "Fat is a good lubricant and provides a lot of perceived moisture. When people call a baked good moist, it is actually a lot of fat," states Widlak.

Hydrocolloids and humectants help baked products retain moisture, in turn slowing staling and maintaining texture. "The reason that some polyols, such as sorbitol, are commonly used in baked applications is that they provide excellent humectancy," says Jamieson. "This property helps to extend shelf life by controlling staling and maintaining a moist texture during the wide range of conditions a baked product can experience before it reaches the consumer." Sorbitol is usually used in this application at 1% to 5%, a level that doesn't impact dough handling or flavor. He adds that if there is flexibility to add moisture into the system, using the liquid sorbitol over the dry provides cost advantages.

"There is not always a single 'silver bullet.' One product does not offer all the solutions the customer is looking for. In a lot of cases, the single enzyme or the single crumb softener or emulsifier most likely will not provide all the textural needs they are trying to obtain in the product," says Widlak. "It is really a complex system that you are trying to control. It's more than just one mechanism that's happening in the food system that is affecting staling, so there has to be more than one solution to help retard it."

In bakery products that derive their texture from sugar, the tendency of sugar to crystallize needs to be addressed. Widlak explains that sugar crystallization can be addressed by adding ingredients that physically separate the smaller sugar particles, such as fats and emulsifiers, or by replacing some of the sugar with ingredients such as corn syrup or polyols that inhibit crystallization. He adds that the humectancy of polyols is an added benefit.

Solubility is an important polyol characteristic. "In a baked application, solubility is key for things like starch gelatinization," explains Jamieson, "which, for example, dictates the spread of your cookie."

Nutrition bars are part of a growing segment where ingredients' nutritional value constrains formulation. Maltitol syrups work well in baked products to control shelf life, especially in products such as baked or extruded nutrition bars that contain higher protein levels. "Maltitol syrups function by controlling the moisture in the system through its composition of varying molecular weight -- similar to that of corn syrups. This varying molecular weight provides a good balance of humectancy, sweetness and functionality to the application," says Jamieson. He adds that even in full-sugar formulations, polyols offer improved stability in texture: "Depending on the corn syrup, a good portion is typically made up of glucose and maltose, both of which are not very soluble. Therefore, they will not bind much water and could potentially crystallize. Something like maltitol or sorbitol -- present in maltitol syrup and/or polyglycitol syrups -- on the other hand, are much more soluble, providing much better humectancy and stability. Interestingly, we see a lot of our customers -- who make sugar-free products -- using polyols in their full-sugar products to extend shelf life."

Adding functional ingredients will depend on the application. Kappelman notes that powdered emulsifiers and enzymes can be blended with the other dry ingredients. However, "in certain applications such as cake, where aeration is desired, optimum functionality can be obtained by melting the emulsifiers into the fat phase before mixing the cake batter," he says.

Doing it to dairy In ice cream, gums stabilize the blend prior to freezing, impart mouthfeel to the finished product and control crystal growth during storage. Prenzno outlines the use of gums in ice cream: "In general, the gum blend is used at concentrations lower than 0.5% and it is dry blended with the other ingredients in the ice-cream mix. The dry ingredients are incorporated into the liquids with rapid agitation, and frequently using high-speed blenders."

A gum blend can meet the texture and stability requirements in frozen dairy products. Rodger Jonas, national business development manager, P. L. Thomas, Morristown, NJ, advises keeping the finished product attributes in mind when selecting gums. "A variety of products can control crystal formation," he says, "but the desired texture and mouthfeel will determine the specific gums and their combinations."

Carrageenan is generally part of the blend due to its synergy with casein. Chavez Surratt claims that locust bean gum and guar gum are "excellent viscosifiers for ice cream," and locust bean gum in particular can "help delay ice crystal growth." She explains that gums take over stabilizing the mix once the emulsifiers have aided the emulsion's creation.

"Tara gum provides freeze/thaw stability and protects the product from heat shock, which is particularly important in ice cream, since this product may go through many freeze/thaw cycles during storage and distribution," notes Prenzno.

Syneresis is the expulsion of water from a gel as it loses its water-holding capacity. Jonas gives the following example of syneresis: "If you are looking at a pudding, take a spoonful out and see the depression filling up with liquid; that is syneresis." Many refrigerated dairy products are susceptible to syneresis. Hydrocolloids and modified starches offer solutions by creating gels with less of a tendency to contract over time, and by reabsorbing water given off by the gel.

In cream cheese, locust bean gum is king. Jonas says that the gum's short, creamy texture is the determining factor, but again: Keep processing requirements in mind. "All gums have limitations and sensitivities," he says. "For example, locust bean gum, to be used properly, should be heated to 85?C. Below that temperature, you will not maximize the use rate and have limited success in the application. This has a definite impact on cost."

Gums aren't the only ingredients that can improve dairy-product texture. Phosphate ingredients provide textural stability to cheese sauces and other dairy products. Emulsifying sodium-phosphate salts exchange ions with calcium in the insoluble calcium caseinate to form sodium caseinate, a soluble-protein form. The finished sauce or cheese texture can be adjusted by selecting specific available salt chain lengths (see the "Phosphate Blends Simplify Processed Cheese Production" Portfolio in the Nov. 2002 issue of Food Product Design for a complete discussion).

Stabilizing dressings and sauces Like ice cream, sauces and dressings are stabilized by a combination of emulsifiers and gums. Chavez Surratt suggests that viscosifiers, other than locust bean gum and guar gum, have more-suitable texture and flavor for this application. Xanthan gum is widely used in dressings due to its acid tolerance and rheology. "Xanthan gum has a property called yield value," she says. "It stays in place as it sits in a bottle or a cup, but once you start to put shear on it, like pouring dressing over your salad, the viscosity relaxes and it allows the product to come out of the bottle."

By providing an increase in viscosity, gums maintain the suspension by increasing the force in the external phase, says Prenzno. "For example," she continues, "when you use xanthan in a salad dressing, you are creating a pseudo-emulsion, the two phases -- water and oil -- are held together because the external phase is thick enough to make it difficult for the internal phase to rise."

Gum blends further improve stability and differentiate dressings from other products in the field. "If you have a six-month shelf life on a high-acid product, the viscosity that you have from a guar system alone will start to degrade. Xanthan and guar combinations will provide more viscosity than either colloid alone, and high ratios of xanthan with guar can provide protection against this acid degradation," says Chavez Surratt. "An interesting combination of xanthan and locust bean gum is in mayonnaise. It forms a slightly gelled texture, and if you tweak the ratio a little bit, you can get a very interesting texture in a mayonnaise product."

Propylene glycol alginate (PGA) does double duty in dressings. Chavez Surratt says it functions like an emulsifier: "It has hydrophilic and lipophilic ends. It also has the backbone of a basic alginate molecule, so it does provide some viscosity, which depends on the grade that you get."

Chavez Surratt describes incorporating the gum into the dressing. First, the gums are dispersed into the oil. Next, the dispersion is introduced to the water under high shear. After allowing 5 to 10 minutes for the gum to fully hydrate, the ingredients in the aqueous portion of the dressing are added. In the absence of oil, the gum would first be dispersed in salt or sugar before being hydrated.

Stabilizing sauce texture will not only depend on the formulation, including pH and other viscosifiers, but also the processes involved. Select modified starches to develop viscosity upon cooking, or in the absence of heating for instant sauces. Once the product's texture is achieved, storage and holding requirements must be addressed. Frozen sauces will benefit from the water-binding gums, such as guar and locust bean gum, as well as modified starches that withstand freeze/thaw conditions. Choose different viscosifiers for a sauce that is held on the steam table for several hours, as happens in foodservice. Ingredients that tend to increase in viscosity over time, like guar gum, or lose viscosity over time, like unmodified starches, would not be used.

Beverage considerations Working with beverages has the challenge of stabilizing a low-viscosity system. "A soy protein beverage where the solids settle down to the bottom of the container is not appealing," says Prenzno. "You need to choose a stabilizing system that provides the suspension without adding too much viscosity. Also, you want it to have an excellent flow behavior and to feel good in the customer's mouth." Product designers commonly use stabilizing systems, including carrageenan, pectin, xanthan gum and CMC, are to achieve these types of characteristics.

"Gums are excellent suspension agents because of their very long chains, which trap other particles," adds Prenzno. "For example, carrageenans are widely used to prepare chocolate beverages since they trap the cocoa particles, providing a homogenous appearance."

Pectin is particularly stable at low pH and is used in beverages to add mouthfeel to reduced-sugar formulations, says Chavez Surratt. Though less tolerant than pectin, CMC is stable at pH above 4, and also finds applications as a viscosifier of beverages. Carrageenen, of course, works particularly well in dairy beverages due to its synergy with casein.

Meeting meats' needs Meat texture not only is impacted by processing, but by the metabolism of the post-slaughter muscle. "With the lactic-acid buildup, it actually starts the changes within the muscle," says Peter Oberacker, Jr., technical service manager, Budenheim GS Industries, Plainview, NY. "The protein starts to get denatured and the actin and myosin, the filaments in the muscle, start to collapse in on one another. It expresses out water." This tends to make meat dehydrated and tough.

"When moisture comes out of the meat it is called purge," explains Sumesh Hirway, Ph.D., senior principal food scientist, Griffith Laboratories, Alsip, IL. "One of our jobs as an R&D scientist in the meat area is to use a number of functional ingredients which can keep the moisture and the fat and the flavor in the protein."

Phosphate ingredients can impact meat texture. "Phosphate, particularly diphosphate, will be a very close match to the adenosine triphosphate, ATP, which is naturally in the animal. It will help buffer the pH of the muscle back up, and allow water to rehydrate the muscle," explains Oberacker.

The salt-phosphate marinade finds application in a wide range of products. Oberacker explains that diphosphate buffers the pH of the muscle up to levels that allow the actin and the myosin to bind water, offsetting the pH-lowering effect of metabolism. The salt allows the phosphate to penetrate the muscle by cleaving the salt-soluble proteins. USDA regulates the amount of phosphate in meat to 0.5% on a finished-product basis, but lower levels can often meet the water-holding need.

Water hardness is often overlooked during formulation. "Phosphates are chelators of heavy metal," says Oberacker. "If you have very hard water with a lot of magnesium and heavy metals in it, the minute you add phosphate it gets tied up with those heavy metals and gets less functional. We will suggest a level of phosphate to use with the hardness of the water in mind. If you have hard water, we will suggest a little bit more, up to 0.5%; if you have soft water, you can use a little bit less."

Carrageenan can also hold moisture in meat and improve texture. "Kappa is the most common form used in the meat industry," says Jonas. He notes that use of new, cold-water-soluble carrageenans is on the rise "as a result of the improvements in yield, as well as the sensitivity of kappa to nonsodium salts and its tendency to leave white streaks in the meat. The iota form makes a very soft gel, akin to slippery water, and is thermoreversible." Although non-cold-water-soluble forms of iota carrageenan are not used in raw meats, it might be used as a blend with kappa carrageenan in cooked applications.

Starch can be hand picked to meet the meat's processing and formulation requirements. "Different starches have different functionalities in certain applications. For example, a particular starch that you would use for an injection marinade could be very different from another starch you would use in an emulsified product. Likewise, a particular starch can generate greater yields in meat products if freeze/thaw stability isn't an issue," states John Randall, vice president and general manager, Penford Food Ingredients Co., Englewood, CO.

"It's just a balancing act of finding the right starch for the right system to give the nice, real-meat texture and also the nice moisture that is delivered upon eating it," stresses Joe Formanek, Ph.D., principal research scientist, Griffith Laboratories.

Processing impacts choosing functional ingredients. "In a rotisserie bird, you want to control purge as you inject it, through transportation, and throughout the cooking process and the holding period in the store," says Joel Reiman, senior food scientist, Griffith Laboratories. "If we are talking precooked, frozen products, then we need to be concerned about water management during the freezing process, during potentially another thaw process and reconstitution. Depending on the process, there are many steps where you will need to control purge, that is where a variety of different functional-ingredient classes can come in."

In putting a system together for foodservice, "we are looking at designing precooked meats that eat well in the store. The main thing is they eat well -- they taste good and have the right amount of moisture in them. To get that balance of quality moisture and quality eating, quite often it is necessary to look at a three- or four-functional-ingredient approach," states Reiman.

The need for water binding and viscosity in process is also a consideration. "Think about hydrocolloids for injection, or adding to chopped and formed products where you are looking for more of an instant swelling to help capture the marinade into the raw system so that it is there when you cook it," says Reiman. "If you look at your soy protein, starches and fiber, like oat fiber, those are going to be more functional through cooking."

Other processing and packaging methods can help minimize water loss in meat. Lisa Sprang, director, Griffith Laboratories, advises that damage from freezing can be minimized if the frozen storage temperature is held constant and the meat is frozen quickly to form smaller ice crystals and thawed slowly to allow the water to be absorbed back into the muscle.

"If you use a vacuum package, immediately the purge will start," adds Hirway. "One of the newer methods is using what is called a gas flush, so that the atmospheric pressure in the package keeps the moisture from coming out of the meat."

Akins calls texture "one of the most critical components of food palatability." The next time we encounter crumbly bread, gritty ice cream or tough chicken breast, we can take comfort   in the fact that we have the tools at hand to make the world a slightly more palatable place.

Karen Grenus, Ph.D., has eight years combined experience in applied research and product development in the area of dry blends for savory applications. She holds a doctorate degree from Purdue University in Agricultural and Biological Engineering.

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