Few foods call for a single texture. Think of a sandwich cookie: From the familiar snap as the cookie breaks, the creamy filling and the softening crumble as it is eaten, multiple textures come into play at different times throughout the eating experience.
With today’s foods and beverages, texture challenges have expanded to incorporate hurdles created by nutritional characteristics. Two of the most prominent examples of this would be the gluten-free movement and the drive to reduce sugar. The need to mimic the structures and, consequently, textures imparted by the elastic gluten proteins affects every aspect of the formulation.
Constantly expanding consumer expectations and demands keep ingredient makers and product developers busy. Yet there is always more to learn about texture, with new insights to be gained through emerging technologies, analyses and ingredients.
A reflection of this heightened focus on texture was noted in a review published last year in Food Research International by Lan Chen, Ph.D., et alia. Titled, “Texture measurement approaches in fresh and processed foods,” the review noted that the number of publications on food texture increased by more than 200% during the past decade.
Just as there is a myriad of styles and types of paintings, there are thousands of combinations of protein, fat and carbohydrates processed via baking, extrusion, heating, shearing, melting and many other production techniques. Finding the right combination of ingredients to fit a particular application and product description can be complicated and time-consuming.
Starches, gums, fibers and saccharides of various lengths and shapes are all carbohydrates. So, too, is sugar— sucrose, a disaccharide of glucose and fructose. Sugar is universally associated with the sweetness it imparts; but in many formulations, especially baking formulations, it is one of the primary ingredients for texture. It also is one of the most versatile and widely used components in food formulations in general.
The simple carbohydrate modulates not only the taste, but also the volume, mixability, preservation and other processing characteristics. Sugar helps give baked goods their bulk; bread its crispy, brown crust; and contributes tenderness to cakes and muffins. Sugar also reacts with the other components in foods, the baking and processing conditions, and even aids in preserving jams and jellies.
While sugar doesn’t have a simple set of performance characteristics, it seems to do everything and be everywhere for a number of reasons. It could be compared to white paint, which is added to paints of all other colors to modulate shades and tints. Sugar modulates textures to varying degrees, depending on what other components are present and how they are processed.
During the past decade, however, foods rich in sugar have been increasingly criticized, because sugar, as with most single ingredients, can be detrimental if consumed in excess. Global concerns regarding rising indices for obesity and diabetes have pointed to excess sugar consumption as a primary culprit.
Reducing sugar consumption has become a goal for most consumers, public health advocates and authorities over the years. And, while reducing labeled sugar has been a priority for food companies for some time, it recently has become more urgent. The “2012 Health Focus Trend Survey” reported that 30% of consumers say that they have reduced their sugar consumption during the past two years.
In 2002, the Institute of Medicine first proposed distinguishing “added sugars” from sugars intrinsically occurring in foods. Consequently, in March of this year, the USDA proposed that added sugars be separated and quantified on the Nutrition Facts Panel. Public health authorities agree and are advocating that consumers should decrease their consumption of foods with added sugars in favor of increasing more nutrient-rich foods. And they suggest that labeling the quantity of added sugars on the Nutrition Facts Panels would assist in achieving this goal.
The FDA’s proposed regulations include a new definition for added sugar. If the definition is adopted as proposed, food formulors seeking to reduce added sugar will have significant formulation limitations and texture challenges. Most processors already are facing multiple challenges in building back texture after reducing sucrose and other ingredients now being termed “added sugars.”
The Texture of Sweetness
While artificial sweeteners; stevia, monkfruit, and other natural sweeteners; and natural-flavor taste optimizers might be able to reproduce the flavor and sweet taste of sucrose, the real challenge remains in replicating the textural benefits that result from sugar in a recipe. That’s where other carbohydrates and similar ingredients come in. The list of such ingredients used to replace the bulk of sugar is growing, as ingredient scientists tease functionalities out of them which were unheard of a generation ago.
These ingredients include starches, gums, polyols, oligosaccharides, resistant dextrins, polydextrose, other dietary fibers and maltodextrins, among others. Selection of specific ingredients for a particular application is essential to achieve an optimum texture.
There is no perfect solution for the versatile functional properties of sugar. Foods with reduced sugar often have a slightly different texture. They bake or process differently or can have a different color, due to the loss of Maillard reaction browning and caramelization.
For example, baked goods and beaten egg foams can be less airy, and puddings can require different mixing procedures to ensure adequate dispersion of the proteins. All of these differences could be noticeable by attentive consumers. This might be acceptable, if the food is a new brand or a new product, but much less acceptable if it is within an established brand or food.
A recent review published in International Journal of Food Science and Technology by Susanne Struck, Ph.D. and colleagues at the Technical University of Dresden, Germany, summarized the use of artificial, high- intensity sweeteners, tagatose, fructans; and bulking agents, such as polyols, to replace sugar in sweet baked goods. While the review presented the state of the art in ingredient technology that addresses texture and flavor challenges of sugar reduction, it also acknowledged that, still, “the replacement of sucrose with bulking sweeteners can result in products with a similar body but a lack in taste and flavor.” Another recent study showed that oliggofructose can successfully replace up to 30% of the sugar in cakes with a texture and flavor that was acceptable, as tested by a sensory panel. Still, replacing sugar with oliggofructose in cakes resulted in lower cake height, due to the decreased starch gelatinization and protein denaturation temperatures.
Sugar-reduced cakes have less time to expand and achieve a proper height. Sugar replacement also caused reduced cell area, and total cell area within the crumb also decreased significantly. But, while replacement of 50% of the sugar with oliggofructose was too different to be acceptable from a sensory perspective, the 30% sugar replacement level worked well and was successful.
In another study, Susann Zahn and her colleagues at Technische Universität Dresden in Germany reported that a combination of rebaudioside-A and polydextrose or inulin worked well when replacing 30% of the sugar in muffins. Formulations with other sources of fibers were not as successful in this study.
If sugar is the canvas of texture, then gluten is the glue that holds the canvas together. It provides the backbone for many formulations, as well as for coatings and other structural recipes. This is especially for true for baked goods—and most especially for bread, which relies heavily on gluten’s textural properties.
It’s no secret that there has been tremendous growth in new products and ingredient solutions for gluten-free applications over the past few years. While the public health awareness of celiac disease (CD) and gluten intolerance has grown significantly, consumer demand has soared. Although celiac disease affects about 1% of the U.S. population, experts estimate that as many as 10% have a related and poorly understood condition known as non-celiac gluten intolerance (NCGI), or gluten sensitivity, according to the National Foundation for Celiac Awareness. Still, it is estimated some 5-10% of the population adheres to a gluten-free lifestyle and up to 30 million or so more admit to “trying to avoid gluten.” Sales of gluten-free products are expected to top $5 billion in the coming year, according to Packaged Facts Inc. This follows a near-doubling of the market between 2005-2010, according to Euromonitor and other consumer research sources.
With those kinds of numbers at hand, processors have realized the gluten-free market has passed the threshold from fad to trend. The pressure is on to continue to create products without gluten that can mimic those containing the protein. (See “Gluten-Free Formulations,” April, 2014, http://bit.ly/1ma0Arc.)
Bread has been the most difficult application to recreate. Some processors have overcome the textural issues of creating gluten-free breads that have the same performance and organoleptic characteristics of their gluten-containing versions. A recent review published in Comprehensive Reviews in Food Science and Food Safety, by Vanessa Capriles, Ph.D., et al, at the Universidade Federal de São Paulo in Brazil, provides great insight on the multiple approaches to producing gluten-free bread.
A number of starches have been developed and refined to accomplish the sort of one-to-one replacement needed by baked goods manufacturers. Typically, these contain a combination of rice, corn potato and/or tapioca flours, coupled with a gum ingredient. Also increasingly applied are waxy-maize and waxy-rice ingredient systems. These are typically used to replace a portion of gluten-containing flours in order to fine-tune final product texture.
Hydrocolloid gums and proteins are extensively used to replace the binding properties of gluten in most applications. Xanthan and guar gum, probably the most common currently in use for this function, provide up-front viscosity in applications. However, they must be used at low levels to manage the viscosity, processability and mouthfeel of the foods.
Starches and gums also are key ingredients in gluten-free applications, because they help to manage moisture, provide binding and reduce the crumbliness and dryness of gluten-free foods. Modified starches have been successful in sweet goods, because they enhance shelflife and aid in preventing the staling that occurs with native starches due to retrogradation.
Potato-based maltodextrins that build up solids also are used for their ability to provide minimal viscosity and act as a flavor carrier across a number of food applications. Instant starches also are being used, because gluten-free applications might not reach the high-moisture and high-temperature conditions required to cook out native starches.
Non-traditional grain blends also are rapidly growing for gluten-free applications. Carob germ flour has been shown to increase the viscoelastic properties of gluten-free bread when combined with corn starch. In addition, ancient grain blends are attractive solutions for natural- market positioning.
The Capriles study cited includes an overview of the use of sorghum, millet and pseudocereals (e.g., buckwheat, amaranth and quinoa) in gluten-free breads. Flax seed, already popular for its health benefits (such as omega-3 oils as alphalinolenic acid) contributes to building texture, but the selection of the right flax seed ingredient is important—as results can vary depending upon which flax seed ingredient is utilized and how it was processed.
Beyond baked goods, other formulations have sought texturants that can overcome the challenges of removing ingredients, such as proteins in the form of eggs or dairy (specifically casein or whey). Too, some processors have sought to remove chemically modified ingredients, such as propylene glycol alginate—a common emulsifier—from their formulation.
Starch compounds also are seeing increased usage as microencapsulation coatings for flavorants or for creating emulsions.
To replace egg and dairy proteins, highly soluble, enzymatically treated starches and maltodextrins. are increasingly used. They’ve been applied with success in dry mixes, beverages, dairy, icings and glazes, as well as utilized for enhancing the spray-drying process and as carriers for other ingredients.
Such usages require these ingredients and ingredient systems to be highly soluble, dispersible, and heat-, acid- and shear-stable. They also must be able to withstand the cook/freeze/thaw/reheat cycle without negatively impacting texture. Typically, they must maintain a low viscosity and have minimal impact on flavor or sweetness.
High-solubility, enzyme-treated starches from non-grain sources such as potatoes also can be used to enhance the crispy texture of coatings and breadings in baked and fried products. Moreover, these new enzyme-treated starches also may be used—instead of dextrins—to improve hold times for fried or baked items such as coated vegetables, meat and poultry (including bone-in offerings) and even seafood. In extruded applications, these starches have been shown to be effective at increasing the puffing of cereals and snacks, even when used in conjunction with dietary fibers and resistant starches that typically impede puffiness. In certain applications, they have been able to provide textural improvement over grain-derived, natural starches.
Tribology and FOP
Some approaches for textural maintenance and improvement are more innovative and attempt to understand more thoroughly the interface between texture and perception. They seek to model or understand changes in food textures as they change during the mastication process (as the food solids become more degraded and moisturized as they are manipulated within the mouth).
This aspect of texture is important, because many perceptions of organoleptics (e.g., creaminess, fattiness, overall mouthfeel) change as the food degrades after chewing. But these changes also are notoriously hard to capture by traditional instrumentation methods. Enter “tribology”—the study of interacting surfaces in relative motion. Tribology studies friction and lubrication between interacting surfaces in relative motion, and the discipline now is being applied to foods. While traditional instrumental analyses are most applicable to foods until and through the first bite, tribology more specifically targets what happens to food between the first bite and swallowing. Until recently, this has been a significant gap in the knowledge of food texture.
Another description for this system in studies is “food oral processing.” This refers to the description of the process of chewing solid foods to smaller particle sizes, mixing with moisture (i.e., in the form of saliva) to form a bolus, which is then swallowed. One research team has proposed that six stages of food oral processing should be considered: (1) first bite, (2) “comminution” or chewing, (3) granulation, (4) bolus formation, (5) swallowing and (6) residue in the mouth.
Food oral processing proposes to further analyze each stage of oral processing. As an example, one new study reported that the plasticization of bread by water/saliva had more effect on the rheological behavior of the bolus than its fragmentation.
Recent research using this methodology is focused on building correlations between friction coefficients and texture concepts, such as smoothness, fattiness and creaminess. Currently, great strides are being made in relating tribology to sensory, but there is not a simple friction coefficient that can predict a texture or mouthfeel attribute.
Large ranges of different configurations are being used and are not particularly well-defined. “It is very much reminiscent of the development of texturometers in the 1960-1970s before a universal texture analyzer was created,” concluded Jason Stokes, Ph.D., et al, in an article published last year in the Current Opinion in Colloid & Interface Science. Rhonda Witwer is a business development and marketing expert in functional foods and nutraceutical ingredients with more than 20 years of experience developing integrated solutions to meet scientific, regulatory, consumer and business needs, and in communicating the benefits of scientifically based ingredients. She can be reached at firstname.lastname@example.org or through Prepared Foods.
New Developments in Analyzing Texture
Historically, a combination of sensory and instrumental measurement has been utilized to measure texture. For example, texture analyzers measuring mechanical responses to a compression—i.e., mimicking bites of a food sample—report on aspects referred to as hardness, elasticity, adhesiveness, cohesiveness, brittleness, chewiness and gumminess. These parameters are combined with sensory perceptions to understand the texture profile.
One research group developed a technique called simulated micro-baking. Julia Rodriguez-Garcia, Ph.D., and colleagues at the Universitat Politècnica de València, in Spain, heated a sample of batter on a microscope slide to simulate baking conditions in order to comparatively measure the development of air bubbles.
A clear effect of sugar replacement could be seen, as the air bubbles became less numerous and larger due to reduced viscosity of the batter. As sugar retards the setting of the cake structure and allows longer time for the gases to expand, reduced-sugar cakes would have been expected to have smaller bubbles, but this was not the case. In addition, sugar replacement resulted in better bubble characteristics than the same level of fat replacement.