Texture Tricks

Texture is magical. The way a food feels affects the way we perceive its appearance, aroma and taste. And while manipulation of mouthfeel can seem mysterious, many tricks can help developers create and maintain the perfect texturebe it real or illusion.

The texture effect 

Consumers rely on texture as an indicator for many different qualities of the foods they eat. Some textures might imply a lack of freshness: carrots that are soft or limp, bread that is hard, or a stick of chewing gum that crumbles. In other instances, texture becomes the pivotal characteristic on which consumers base their preferences. They may love the flavor of banana bread, but not be able to eat a plain, old banana, because of the soft texture. Many people love ketchup on a burger, whereas a slice of raw tomato draws only a no thank you. Crackers should be hard and crunchy, but not bread. A survey of pickle consumers revealed that 90% of respondents define a good pickle as crisp, firm and hard.

Any number of components in a product can affect texture. Removing sugar from a beverage application and replacing it with a high-intensity sweetener lowers viscosity and changes the products mouthfeel by eliminating the tongue-coating effect of the sugar in the original formulation. Reducing salt in a formulation can also result in decreased viscosity. Decreased levels of citric acid will also affect perceived, as well as measured, viscosity. Some of the changes can be caused by reduced soluble solids, and some by potential ingredient interactions, depending on the formula.

Formulating reduced-fat products presents similar issues. Fat in a food system affects texture, mouthfeel, pliability and even shelf life. Fats multifaceted role in foods typically necessitates combinations of ingredients to recreate the many characteristics lost when fat is removed.

Building the right texture can also affect the appearance of a product. Particulates that are not suspended properly will float to the top or sink to the bottom of a container. Overdeveloped thickness of a fluid can hinder the processors ability to pump or fill the product, as well as cause uneven heating or cooling.

Texture can be defined by a number of characteristics, including viscosity, smoothness, softness, hardness, rigidity and elasticity. In addition to, and perhaps even beyond, a products texture, is the mouthfeel, measured in terms of dryness, lubricity, smoothness, sandiness or fluffiness. Any one of these terms might represent a persons impression of texture, but it is really a combination of pieces that interact to complete the texture puzzle. The multifaceted nature of texture is what makes quantifying and reproducing it so difficult.

Knowin how its flowin 

Viscosity is one of the most common contributors to the texture of a food or beverage. Viscosity measures a fluids resistance to flow. If you tilt a glass of water and a glass of corn syrup, the water will run out more quickly, because the water has lower viscosity than the corn syrup. Viscosity can be affected by temperature, though. At elevated temperatures, the corn syrup will exhibit much lower viscosity than when cool.

Flow further distinguishes the characteristics a fluid exhibits. In 1687, Isaac Newton suggested that a fluids resistance to flow, viscosity, is proportional to the velocity at which the fluid is being separated because of said flow. Newtonian fluids are those whose viscosity is not affected by shear rate or time. No matter how fast you stir it, it still flows the same way. Non- Newtonian fluids, on the other hand, exhibit various degrees of change with varying levels of shear. If you stir a bowl of pudding or ketchup, you will leave a hole that will fill up when the shear (stirring) is decreased or eliminated. Non- Newtonian materials, the category into which most foods fall, are further separated by their specific behavior under, or in response to, shear stress.

For some materials, flow will not begin until a certain level of shear stress is applied. Once this yield value is reached, flow begins and is not affected by variations in shear rate. These are called Bingham plastics. Pseudoplastic fluids exhibit decreased viscosity with increased shear and are sometimes referred to as shear thinning, although this is not entirely correct, as the viscosity will return when the shear forces are removed.

Pseudoplasticity is independent of time, as flow rate changes occur immediately with changes in shear. The change is not, however, linear. Pseudoplastics can have a significant yield value, a desirable characteristic in emulsions or suspensions that require pumping or pouring. At rest, these systems will not flow or separate. Upon pumping, though, the fluids move easily, with less energy input than required to pump a product with the at-rest viscosity. A good example of pseudoplasticity in action is the behavior of xanthan gum in salad dressings. You shake the dressing up so it will pour onto your salad. But once on the salad, the dressing stays put.

The opposite of pseudoplastic is dilatant. Sometimes referred to as shear thickening, dilatants exhibit increased viscosity with increased shear. Although rare in food applications, examples of dilatancy in foods include very concentrated suspensions of starch, candy compounds and peanut butter.

Plastics, also referred to as viscoplastics, behave like a solid when at rest. One must apply a certain level of force to the material before flow will begin. The level of force needed is called the yield value, and it will vary by product. A good example of plastic behavior is ketchup, which often requires that the bottle be shaken or struck before the product within will flow out. Once the yield value is reached, the material may exhibit characteristics of Newtonian, pseudoplastic or dilatant flow.

Non-Newtonian flow may also be time-dependent. A pseudoplastic fluid whose viscosity gradually decreases under a constant rate of shear is referred to as thixotropic. When shear force is removed, the material will gradually regain viscosity. Not all materials will return to their original viscosity.

Rheopectic flow is characterized by viscosity increasing over time at a constant shear rate. As with thixotropy, the effect may or may not be completely reversible. Rheopectic flow is rarely encountered in food systems.

Just gellin 

Gels form when molecules of a given gelling agent interact to form three-dimensional networks. The texture of a gel is difficult to define, as the perceived mouthfeel rests not in a single moment, but every moment of consumptionthe way the product breaks during the first bite, how it shatters or smears across the tongue and palate during mastication, and how long it takes to reduce the product from its original size, shape and consistency to that which is swallowed. And the characteristics that affect the perception at each of these stages of consumption are numerous.

Means of gelation refers to the driving force behind gelation. Chemical gelation is driven by acidity or ionic factors. Examples of acid-driven gelation include sodium alginate and high-methoxyl pectin in the presence of sugar. Ionic gelation can be observed with sodium alginate (Ca2+), as well as kappa and iota carrageenans (K+and Ca2+, respectively).

Gels formed by heating or cooling are the result of thermogelation. Agar and gelatin gels form after cooling a hot solution, while heating will cause gelation of hydroxypropylmethylcellulose and methylcellulose.

Gels may be reversible or irreversible. Gelatin and carrageenan set into gels when cooled from a hot state, but will revert to a liquid state if heated again. Conversely, hydroxypropylmethylcellulose and methylcellulose will gel when heated, but return to a fluid state when cooled to room temperature.

Adding it all up 

Scientists have proposed various systems for evaluating food products texture and mouthfeel based on the factors they consider to have the greatest effect on how the product is perceived. Alina S. Szczesniak, a scientist with General Foods, White Plains, NY, developed a set of standards for classifying a foods rheological properties based on three categories of textural character:

Quantifying textural attributes has become more sophisticated through the years. The science of rheology (the study of the deformation and flow of materials) quantification uses a number of techniques, such as advanced sensors with an array of probes plates, pistons, cones, needles, knives, balls and even simulated teethpushing against, into and through samples. Fluids can be evaluated by measuring resistance to rotation of metal cylinders, discs and tees, and other methods like the speed of a falling ball or measuring flow in relation to time. Sophisticated computer programs can analyze data from many of these tests to provide indications of textural attributes such as gel strength, film strength, break point, hardness, softness, smoothness, lumpiness, slipperiness, stickiness and spread ability. By correlating mechanical data with organoleptic data, developers and processors can often use instrument systems to quickly, accurately and economically evaluate products throughout the developmental or production process.

Tricks of the trade 

Differences in gelling and melting temperatures are common tools exploited by food scientists, notes Joe Klemaszewski, senior scientist, dairy applications, Cargill Texturizing Solutions, Wayzata, MN. The gelling temperature of egg-white proteins helps baked products hold their structure after baking, he says. Replacement of the egg protein with a protein that sets at a different temperature results in a loss of volume. Temperature- viscosity profiles can be varied to affect finished product and processing attributes. Gelatin is easy to process because of its low viscosity above its gelling temperature. Upon cooling and setting, it forms a thermoreversible gel. In contrast, hydroxypropylmethylcellulose thickens on heating and loses viscosity on cooling. Starches build viscosity on heating and build additional viscosity when cooled. These properties can be used when making pie fillings to maintain particulate identity during heat processing or to maximize heat transfer.

Thermoreversibility can be an important consideration when looking at end use, as well. Gelatins low melting temperature (77º to 82ºF, or 25º to 28°C), depending on the soluble solids of the product, provides very desirable mouthfeel and flavor release in gelled desserts. On a buffet, however, where consumers may place the gel onto a warm plate, or close to warm food items, the gel can begin to melt. Carrageenans can create a similar texture as gelatin, but with a higher melt temperature. For example, a carrageenan and locust bean gum blend can have melt temperatures above 97°F. The gel will be more stable on the warm plate, while still melting in the mouth of the consumer.

Comparing gelling agents, developers must not overlook possible effects on flavor. The low melting point of gelatin will release flavoring compounds more readily, resulting in a higher perceived flavor intensity. Higher melt temperatures for carrageenan gels can give the perception of lower flavor intensity. This same relationship holds true for aromatic impact of the gel.

As consumer demand for healthier products grows, so does the need to replace the mouthfeel of the fat removed from the traditionally formulated products, observes Joshua Brooks, vice president of sales, Gum Technology Corporation, Tucson, AZ. Whether it is for a reduced-fat mayonnaise-type dressing, or a reduced-fat chocolate- chip cookie, he says, if the mouthfeel of fat, such as smoothness or creaminess, are reduced, then you need to replace them with an ingredient which will mimic these properties.

Brooks suggests a specialized blend of gumscellulose gel, konjac and xanthan gumto create a gel structure that mimics fat. Hydrocolloids in the blend also provide a water-binding effect that can extend the shelf life of certain fresh and frozen products. In baked goods, for example, the stabilizer reduces staling. In frozen applications, the blend helps control ice crystallization, he says, noting that usage levels ranging from 0.25% to 1.00% of total formulation will not mask flavor.

Developers can also take advantage of the individual components of stabilizer blends for use in specific applications. Many gums require heating in order to crosslink at their molecular level, which results in their gelation upon cooling, says Brooks. The cellulose gel component of the aforementioned blend allows for this stabilizer to gel without heating. Gelation induced under cold conditions will, however, be slightly weaker than one formed by heating and then cooling.

Additional ingredients can enhance stabilizer blends to make them more suitable for a specific application. A stabilizer comprised of cellulose gel, konjac and xanthan gum could incorporate sodium alginate to react with calcium present in dairy applications and further promote gelation in dairy formulations, adds Brooks. Such applications include reduced-fat milk puddings, reduced-fat cheese dips, reduced-fat cheese sauces, low-fat yogurt dressing and reduced-fat smoothies. Usage level would be as low as 0.10% to 0.50%.

Faux fat 

With fat replacement, developers must consider not only the loss of flavor from removed fat, but also the other flavors in the product. Fat, in traditional foods, provides texture and taste. It also serves as a carrier for lipophilic flavors. Removing fat from a product will increase the rate at which these flavors are released, causing an initial burst of flavor rather than the steady release of flavors provided by the full-fat formulation.

Traditionally, starch has been used in these products to stabilize viscosity and to improve process tolerance. Specialty starches can be included in yogurts and puddings to improve two of the main dimensions of texture that account for creaminess in yogurts and puddings melt-away and mouth coating, notes Marshall Fong, marketing director, National Starch Food Innovation, Bridgewater, NJ. The different intensities and combinations of intensities in these two important attributes cover the range of consumer experiences, from a caramel-like texture to one more like crème brûlée.

Adding specialty starches on top of the base viscosifying starches can provide different levels of mouth-coating and melt-away, says Fong. Adding a modified tapioca starch on top of a modified waxy maize starch gives high mouth-coating and low melt-away. Adding a specialized maltodextrin instead gives low mouth-coating and high melt-away.

Polydextrose can help provide some of the missing textural properties in higher-moisture reduced-fat products. It readily absorbs water and provides more viscosity than equivalent concentrations of sucrose or sorbitol, possibly because of its highly branched structure. This bland, single-calorie-per-gram polysaccharide is composed of randomly cross-linked glucose and can provide prebiotic fiber and bulk, that, when hydrated, also gives a fat-like mouthfeel. For example, in a cake product, it can replace a significant portion of the fat in the original formulation, maintaining mouthfeel without affecting the expansion properties that determine crumb structure.

Combing unique functionalities of whey protein concentrates offers developers the ability to tailor a finished mouthfeel to meet a specific target. For instance, using two productsone to provide a slippery note, while another provides a heavy mouthfeel texture and cream and/or milk-like flavor is an excellent way to reduce or replace cream in various formulations, says Michelle Ludtke, senior food technologist, Grande Custom Ingredients Group, Lomira, WI. These products have seen great success in the sauce and dip area, as well as bakery, frozen desserts, soups and dressings.

Whey protein concentrates may be added as dry ingredients, although Ludtke recommends mixing with water. Although we have seen that blends of dry ingredients work well, it is ideal to be able to hydrate whey protein concentrate and water together to give it the very best chance to maximize the functionality and economic benefit, she says.

Reclaiming the magic 

The average consumer might not think about the texture of a beverage until its gone. Sugar-free versions of a familiar drink can regain the textural attributes of the removed sweetener by adding about 0.10% high-methoxyl pectin. Pulp-free fruit juices can regain mouthfeel with a similar addition of pectin.

In beverages, one of the simplest, yet proven, offerings is modified tapioca starch, which is available in a variety of versions, including instant, says Fong. The simple addition of 0.5% to nonfat milk, for example, would move the sensory perception of viscosity, shape and mouth-coating to that much more similar to that of whole milk. Viscosity, shape and mouth-coating are precise sensory terms related to the consumer experience of thickness, fullness and creaminess.

Carrageenan serves a dual role in chocolate-milk applications. The soft, pourable gel network suspends the cocoa particles in the milk, preventing a brown sediment at the bottom of the container. Additionally, the gel creates a rich, full-fat mouthfeel, even though a low-fat base material is used.

Presto change-o 

While a texturizing agents functionality may seem clear, circumstances may arise that allow an altogether different character to emerge. Xanthan gum, for example, is a consistently reliable thickening agent across pH of 1 to 12, with minimal effect from temperature. Xanthan solutions are pseudoplastic, however, meaning that a very thick solution at rest will exhibit very little apparent viscosity when pumped. Thick or thin, though, its always a thickeneralone. Now, add another thickener, locust bean gum, and presto! You get a very elastic gel.

Locust bean gum can also be added to kappa carrageenan to increase elasticity. Normally very rigid and prone to syneresis, locust bean gum increases solution viscosity and gel elasticity while reducing the amount of syneresis observed. The effect simulates a gel made with iota carrageenanmore elastic than kappa with lower syneresis. Locust bean gum is, however, less expensive than carrageenans, providing developers an economical alternative for creating the desired texture.

Another unique synergy can be observed by combining xanthan gum and konjac. Formulators are now using these gums in combination, because they form an extremely elastic gel texture, says Maureen Akins, lead food scientist, TIC Gums, Inc., Belcamp, MD. Were seeing these gums used to add texture to applications like pie fillings and chewy candy. When added to beverages, this combination provides exceptional suspension characteristics at extremely low usage levels of 0.05% or less.

Another textural double agent is sodium alginate. When alginate is used without calcium, notes Akins, it builds viscosity. When calcium is added to the system, it forms a gel. This texture trick is the subject of a lot of interest in the culinary world recently as chefs use alginate to form caviar-like gel beads. The food industry has employed this technology for many years to create the omnipresent pimento strips stuffed into olives, and more recently for restructured foods, such as fruit bits, onion rings, and uniform meat and fish shapes.

There is a wide variety of gummy creatures these days, each based on the traditionally formulated bears where high-bloom gelatin creates a very firm, elastic texture.

Formulating with pectin or agar, though, will yield a tender, short texture. Gumdrops made with thin-boiling starch will be chewy and sticky. By working with combinations of these texturizing agents, developers can create any number of unique signature textures within the category of fruit gummies.

As any good magician will note, the most-important bit of any trick is the setup. When adding a stabilizer, it is always best to start with a low usage level and adjust incrementally, says Akins. To get the most cost-effective use of the lowest-possible stabilizer level, its important to follow hydration guidelines such as available water, sufficient dispersion, order of incorporation, and appropriate hydration temperature.

Once you have a grasp of the basics, its time to perform textural magic.

R. J. Foster is a communications specialist with over 15 years of experience in the food industry ranging from technical service, research & development, quality control, regulatory and technical sales. He can be reached by e-mail at [email protected].