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Protein, A Functional PowerhouseProtein, A Functional Powerhouse

Kimberly Decker

May 22, 2009

19 Min Read
Protein, A Functional Powerhouse

Proteins are about a lot more than the latest headline-grabbing diet fad or nutritional wonder. Protein may be the most valuable arrow in the product developers quiver. But its packed with paradox. It can be a handy tool and a finicky reactant, a potential allergen and a vital macronutrient, a formulations salvation and its Achilles heel.
Protein is so very functional in so many different ways, says Starla Paulsen, applications department manager, Glanbia Nutritionals Inc., Monroe, WI, that to turn those functions to your favor, you really have to understand what youre working with. You have to have some sort of matrix to build structure in food. And one of the major ways you can get that is with protein. Its the gluten network in bread dough. It forms gelatin gels, cheese curds and yogurt. It stabilizes salad dressings and heat-set foams like meringue. And, its the very muscle tissue that we eat as meat.

Going against nature
All of proteins functional propertiessolubility, water-binding, viscosity, foaming, gelation, emulsification, film-formingdepend on its physical conformation.
Protein structure starts with 20 commonly occurring amino acids linked in peptide bonds to form a linear sequence. When we alter a proteins structure from its native conformation, we denature it. Extremes of pH, temperature, shear force, salts or solvents disrupt the protein in ways that can exert powerful effects on its functionality.
For example, if you denature a protein, it might not have any ability to form a network to hold air or water, Paulsen explains. That could be disastrous in a formulation, or it could produce precisely the results you desire, as would be the case, she says, if you want a protein thats very inert or doesnt absorb a lot of waterthat just builds bulk and not structure.
Such structural tweaking can enhance water binding, as happens with -lactoglobulin, a relatively heat-sensitive whey protein frac-tion. When heated, the bonds creating the tertiary structure of the protein globules are broken, unfolding of the protein molecules oc-curs, and new protein-protein interactions occur, says Kimberlee J. Burrington, dairy ingredient applications coordinator, Wisconsin Center for Dairy Research, University of Wisconsin-Madison. The unfolding of the product exposes more water-binding sites, so the ingredient will have enhanced water-binding ability. This makes it useful in processed meats, baked goods, sauces and dressings.

A functional solution
Perhaps denaturations most important effect on protein function involves its ability to turn a previously soluble protein insoluble. Because solubility is a precondition for many protein functionswater-binding, foaming, emulsification and gelation among themknocking a protein out of solution may knock it out of function.
Proteins lose solubility near their isoelectric point (pI), the pH at which a protein has no net charge. With no positively charged amino acids to repel each otheror negatively charged ones to do the samethe proteins aggregate in dense, bulky clusters that precipitate out of solution and drift to the bottom of the beaker or bottle.
The implication is that, if solubility is a priority, product designers best work with protein whose pI is not the same as that of the ma-trix. This is why manufacturers formulating with gelatin gravitate toward type-A, or acid-pretreated, gelatin as opposed to base-pretreated type-B. The pI of type-A hovers around pH 9; type-Bs is closer to 5. Thus, type-A gelatin gives manufacturers a lot more flexibility, says Jeremey Kaufmann, senior sales manager, edible and specialty gelatins, Gelita USA, Sioux City, IA. All edible prod-ucts are going to be at a pH significantly less than 9, so type-A gives you a wide range where youre not near that pI. If youre working with gelatin at a pH near its pI, you get strange interactions going on, like influences on clarity, on viscosity, on gelling power.
As an added bonus, notes Mindi McKibbin, associate chemist, Gelita USA, type-A gelatins foam better (why theyre ubiquitous in marshmallows) and are less prone to syneresis (why they often stabilize yogurt).
For beverage manufacturers, the main pI challenge has been finding a protein compatible with high-acid formulations. This, Paulsen notes, is an area where whey proteins shine. With pI values ranging from about 4.2 to 4.5 for the -lactalbumin fraction, and from 5.3 to about 5.5 for -lactoglobulin, whey proteins happen to be one of the very unique proteins in that, as you push them down the pH scale, they become more positively charged, she says. Then the protein repels itself, so it cannot aggregate and it stays soluble in water. This makes it one of the only proteins that you can use at those really low pHs that you find in things like sports beverages.
But, a whey protein may have more trouble in a neutral meal-replacement shake, or a yogurt smoothie whose intermediate pH nearly matches wheys pI. If youre trying to work in that area, you deal with a lot of aggregation, Paulsen says. The proteins are pretty soluble as long as you dont add any heat treatment, but once you add heat, because there is no charge on the proteins, all they do is ag-gregate and fall out of solution.
This can actually be a boon in products where you deliberately seek texture, Paulsen notes. When you start to get those aggregates, it causes viscosity in the beverage. If you figure out how to harness that correctly with the right additives and processingsmoothing out the aggregates with homogenization, for exampleyou can utilize an ingredient you already have in your formula to give you the vis-cosity and mouthfeel that you want, she says.
Another dairy protein choice for beverages is casein. According to Jeffrey Kegel, business development manager, Milk Specialties Global, Eden Prarie, MN, what sets casein apart is that, unlike most other proteins, it doesn't exist in a crystalline structure. It is this that gives them unique properties in various food applications, as they are very resilient and easily manipulated at the same time, he says. Heat tolerance is one casein plus, with the proteins remaining soluble even at retort temperatures. This allows them to work great in UHT or RTD beverages.
 Casein's flexible, open structure also lends it to use in viscosity control. For example, while sodium caseinates increase viscosity in products that need some texture, addition of calcium to the solution completely changes the profile. The changes include the calcium causing aggregation of the casein structure, thus lowering the viscosity, Kegel says, as well as making the product a milky white color because the aggregated protein better reflects light. Depending on the application, he says, a sodium- or calcium-based casein-ate may be preferred.

Starting to gel
For yogurt, Paulsen says, you want to induce protein-to-protein bonding, because you want the protein to form that really strong networkthat gelto hold the water. Gelation is an important precursor to a number of protein functions, from water absorption, thickening and adhesion to emulsifying, foaming and stabilization. Without protein gelation, we wouldnt have coagulated egg white, gelatin desserts, surimi, textured vegetable proteins, bread dough or yogurt.

Paulsen suggests working with whey protein concentrates (WPCs) in yogurt because, at around 34% to 80% protein, they contain enough lipid matter to add mouthfeel, as well as gelation. Its designed to be a nice, full-body-creating ingredient, she says. Some sta-bilization of the gel is still advisable, though. As long as there are any free linkages between proteins, she says, bonds will keep try-ing to form, and the network will just keep squeezing tighter and tighter, expelling more water, and crying out for a stabilizer to hold it in.
One characteristic of whey protein gels is their irreversibility. This isnt the case with gelatin, which forms thermoreversible gels. Unlike many other hydrocolloids, a colloidal solution of gelatin, once gelled, can melt back down with subsequent heating, McKibbin says.
And, because it melts at around 86°Fright near body temperaturethat gives it a special mouthfeel and texture thats a little bit different from other hydrocolloids, like your pectins and carrageenans, Kaufmann says.

The meat of the matter
Gelatin frequently appears in sausages and meat products, where it binds water and builds texture. Just as frequently, youll see soy proteins doing the same. From sausage and ground meats to whole-muscle meats, soy proteins can increase succulence, improve taste and texture, increase yields, and decrease costs, says Courtney Kingery, marketing and customer development manager, ADM Spe-cialty Food Ingredients, Decatur, IL.
Minhthy Nguyen, associate director of technology and innovation, Solae LLC, St. Louis, credits soys globular structure for its gel-ling prowess. What happens with the globular protein, he explains, is that it can swell up and develop a large hydration layer. It has many side chains that are not friendly to water, and theyre in the globule core. But its on the outside of the globule where you have the contact with the hydrophilic amino acids, and thats where youre able to have a lot of water adhering to the surface of the mole-cule.
Paulsen notes that whey protein also works amazingly well at binding water in meat applications. Whether WPCs or isolates work best really depends on what youre trying to get out of it, she says. I would say the most commonly used is WPCs because manufac-turers are looking for a combination of emulsification, water binding and gelation.

Rolling in dough
Emulsification, water binding and gelation all come into play in the formation of dough. The proteins responsible are the glutens in wheats endosperm. While gluten proteins are present in virtually all grains, the ones that form the strongest dough network belong to wheat.
The two gluten fractions most active in dough formation are the high-molecular-weight glutenins and lower-weight gliadins. Both exhibit poor water solubility because their amino acid composition is only sparingly ionizable. But their high concentration of hydroxyl amino acids make them quick to hydrogen-bond and surround themselves in an adsorbed layer of water. Kneading of the hydrated gluten mass mechanically unfolds and realigns the proteins, encouraging disulfide bonding and interactions among hydrophobic amino acids. The result is a three-dimensional, viscoelastic network of membranes that captures fermentation gases and stretches as the dough rises. During baking, soluble albumin and globulin protein fractions denature and aggregate, setting the breads finished structure.
Studies show that glutenins give dough its strength, elasticity, cohesiveness and mix tolerance, while gliadins promote extensibility and expansion for greater volume. Too much of either makes for an inferior loaf, and manufacturers manipulate gluten protein interac-tions to strike a functional balance. Disulfide bonds are especially important to the creation of the gluten network that provides strength and structure in baked applications, says Brook Carson, technical product manager, specialty products, ADM Milling, Decatur, IL. By cleaving those bonds with reducing agents like cysteine, bakers can weaken the dough for better stretch and extensibility (handy in pizza crusts and wheat tortillas), while oxidizing agents like bromate tighten the dough and make it more elastic.
Such manipulations also allow wheat-protein processors to produce functional modified wheat proteins, like isolated wheat gluten, which is an increasingly popular adjunct. In its production, Carson explains, disulfide bonds are broken, relaxing the functionality of the protein. These proteins have a broad range in functionality and can be used in a wider variety of applications.

Low-pH wheat protein isolates exhibit unique film-forming properties in low-water systems, where they act like a very relaxed glu-ten. By whipping the isolate and adding more water, their texture approaches that of egg-white foam. Isolates are being used in cakes, cookies and other sweet goods, providing structure and aeration while maintaining the desired texture and tenderness, Carson says. This allows wheat proteins to be used when formulating for reduced sugar and fat, creating better-for-you snacks. Wheat proteins can also be used when replacing or reducing eggs in reformulating for cost savings.
When used at levels as low as 2% in pizza dough, wheat protein isolates ease sheeting and prevent cracking. A 1:1 blend of wheat protein isolate and water acts as a low-sugar, protein-enriched adhesive in bars and on breakfast cereals. And 2% of wheat protein isolate improves rheology and flavor in whole-grain goods, restoring strength and boosting volume without compromising softness.

Oil and water
Another principle protein function involves emulsion formation and stability. When a protein stabilized emulsion is formed, ex-plains Kevin Segall, Ph.D., food scientist, Burcon NutraScience, Vancouver, British Columbia, the oil phase is dispersed by disruption into small droplets, which become coated with proteins. The proteins orient at the oil-water interface, lowering the interfacial tension with their hydrophobic regions exposed to the oil phase and their hydrophilic regions associated with the water phase. Thus oriented, the proteins keep the phases separate and the emulsion stable.
Factors affecting emulsifying capacity include protein solubilitythe more, the betterand flexibility, which allows the protein to uncoil and adsorb at the oil-water surface more readily. Thus, globular proteins with relatively stable structures, like many whey and soy proteins, dont make the best emulsifying agents unless manufacturers fiddle with their conformation first. With soy, Nguyen says, what we have is a globular protein. Therefore, as is, it wouldnt be expected to be effective at emulsification. But, when we apply pro-prietary technology to it in order to liberate the side groups from its globular structure, we now have very good emulsifying soy pro-teins.
Burrington says whey emulsification properties can be enhanced by controlled denaturation of the protein. The pH and ionic strength of the aqueous phase also come into play, with the presence of salts affecting whey proteins emulsion capacity through their influence on conformation and solubility.
And, notes Paulsen, the fat and phospholipids in WPCs aids emulsification because they make the proteins very stable and very will-ing to participate at the oil-water interface for interaction.
The balance of proteins, lipoproteins and phospholipids in egg yolk offers another example of the right functional combination for emulsification. Egg yolk itself is an emulsion, and mayonnaise, Hollandaise, baked goods, and dressings all make use of its emulsifying properties. Egg yolk emulsions are stable to high shear and low pH, and dont react adversely to ions. Perhaps the most-important func-tional phospholipid in egg yolk is lecithin, but other yolk constituents, including low- and high-density lipoproteins and myelin figures, also aid emulsion stability by sequestering those oil droplets.
The more hydrophobic the protein, the better it concentrates at the oil-water interface to lower surface tension and stabilize emul-sions. Canola proteins, isolated from canola meal occur in two major fractions: high-molecular-weight globulins, and lower-weight al-bumins. One ingredient, comprised principally from isolated canola globulins, emulsifies readily, in part because of the relatively high surface hydrophobicity of the component proteins, Segall says, and also perhaps due to stabilizing steric interactions between droplets, introduced by the dimensions of the absorbed protein. Although the ingredients are just emerging, he predicts their use in a broad range of emulsified applications, including spoonable and pourable salad dressings, sauces, beverages, and processed meats.

Stable airheads
When air is introduced into a protein solution, says Segall, proteins orient at the air-water interface with their hydrophobic regions exposed to the air phase and their hydrophilic regions associated with the water phase, coating the air bubbles and lowering the interfa-cial tension.
Voluminous, stable foamslike meringues, angel food cakes, marshmallows, whipped cream, mousses, soufflés and the head on beeralso require high viscosity in the aqueous phase and a layer of adsorbed proteins strong enough to hold air, yet elastic enough to expand without breaking. The protein qualities that help form foams differ from those that help stabilize them. Foam formation calls upon soluble proteins that rapidly migrate and unfold at the air-water interface. This usually means flexible proteins with limited secon-dary or tertiary structure, and a mild heat treatment may actually aid the unfolding. Stabilization, on the other hand, calls for proteins that form viscous films, called lamellae, that surround the gas bubbles in a continuous, elastic membrane: globular proteins of high molecular weight, for example.

These are all properties of egg white, or albumin, proteins. Able to foam both at their natural pH of 8 to 9 and near their pI of 4 to 5, egg albumin proteins are models of foaming functionality. Ovalbumin is the fraction most responsible for goosing foam capacity, while ovomucin contributes stabilization, making for a rapidly formed foam that retains its volume, even when heated. (Careful, though: Egg white proteins denature and lose their foaming capacity above 136.5°F.) Whipping increases the number and decreases the size of the foams air bubbles, growing the foam and aggregating the proteins at the surface. However, beating for more than 6 to 8 minutes, or at shear pressures above 5,000 psi, can denature the proteins so much that they no longer adsorb adequately.
Other factors affecting egg-white foams include salt, which decreases stability, and sugar, which delays foam formation. Perhaps most important is the injunction against lipid contamination; levels as low as 0.05% can significantly impair foaming performance. This applies not only to egg white foams, but to soy- and dairy-based foams, too. Thats why straight whey protein isolates, with their high concentration of protein, form the best foams among whey proteins. The more protein, the better the foam, says Paulsen.
Canola proteins also show foaming potential, Segall says, although much of the research we have conducted on foam properties has been done in the laboratory with model systems. While his company is just now focusing on applied work, theyve observed that foams made with a canola albumin product achieve both greater volumeperhaps because of the constituent proteins low molecular weightand greater stability over time than those made with the globulin ingredient.

Kimberly J. Decker, a California-based technical writer, has a B.S. in consumer food science with a minor in Eng-lish from the University of California, Davis. She lives in the San Francisco Bay Area, where she enjoys eating and writing about food. You can reach her at [email protected] .

In Bloom
Chemists quantify gelatins gel strength using Bloom, defined as the weight in grams required to de-press a half-inch plunger 4 mm into a standard gelatin solution. Different gelatin ingredients exhibit dif-ferent Bloom strengths, depending on the conditions of their extraction. The first extraction we do on the raw materialusually porcine skin, less commonly bovine hide and boneis usually your highest Bloom, because its processed at a lower temperature, says Mindi McKibbin, associate chemist, Gelita USA, Sioux City, IA. The more extractions you do from the raw material, the lower the Bloom gets.
Bloom values range from around 50 to 300 Bloom grams. As a benchmark, a gummy candy might use 7% to 9% gelatin at a strength of 200 to 275 Bloom grams; a marshmallow 1.7% to 2.5% at 225 to 275 Bloom; and a dairy product like yogurt 0.2% to 1.0% at 150 to 250 Bloom. Usually, the higher the Bloom, the better the color, clarity and taste that youll get, McKibbin adds. Lower-Bloom gelatins are better suited to applications that dont need the gel strength, such as cereal or protein bars that use the gelatin as a binder.
You can get the equivalent of a higher Bloom strength with a 100 Bloom gelatin just by using more, adds Jeremey Kaufmann, senior sales manager, edible and specialty gelatins, Gelita USA.

Cheat-Meat, Version 2.0The Latest in Meat Analogues
Anyone even passingly familiar with the fakin bacon crumbles and not-dogs of the past will agree: The less said about these first-generation vegetarian meat analogues, the better. Whether the products were dry and cottony or dense and gummy, they left little doubt as to what you were eating, and it wasnt meat.
Yet, while early texturized soy and vegetable proteins had their weaknesses, the technologies used to make them demonstrate principles of protein science and engineering that bear review today. Take the thermoplastic extrusion of textured vegetable chunks. The process begins with a mixture of hy-drated soy protein flours or concentratesranging in protein from 45% to 70%that moves through a cylinder where it encounters extremes of heat, pressure and shear force. Once it reaches the proper viscosity, rapid extrusion into the ambient environment causes internal moisture to flash off and creates an expansion of the mass. Cooling transforms the protein mass into a dry, porous matrix that can ab-sorb as much as four times its weight in water, developing a chewy, elastic texture not unlike that of meat. The process relies on good protein solubility, and involves thermal aggregation and coagulation.

While that method sufficed to make vegetarian granules and crumbles, it didnt replicate the myofibril-lar texture of whole-muscle meat. Achieving that requires the spinning of proteins into textured vegeta-ble fibers. Processors usually begin with a solution of soy protein isolate (90% protein or more) ad-justed to a pH above 10. This generates electrostatic repulsions that cause the protein subunits to un-fold and dissociate. As this viscous mass passes under pressure through a die perforated with thou-sands of tiny holes, the protein molecules extend and align in parallel. Following exit from the die, these liquid filaments take a dip in an acid-salt bath whose isoelectric pH coagulates them into a muscle-like structure. Subsequent stretching, compressing and heating further adheres the fibers to one another, and results in a product that looks and feels more like real meat.
Soy protein manufacturers have improved upon these techniques with a new generation of textured soy proteins that replicate whole-muscle and ground meats. These textured proteins are produced in many sizes, shapes, colors and flavors, says Courtney Kingery, marketing and customer development manager, ADM Specialty Food Ingredients, Decatur, IL. Unique textured protein products can be manufactured through the use of combinations of plant proteins or other powdered ingredients, such as various carbohydrate sourcesstarches or fibers, for example.
The result is analogues with qualities more comparable to real meat. We have products that form structures that are very meat-like, very fibrousjust like meat muscle fibers, says Minhthy Nguyen, associate director of technology and innovation, Solae LLC, St. Louis. Such products have made it possible to produce vegetarian analogues that are similar to whole-muscle meat pieces. You can ac-tually have meat-like shreds, he says. Weve even produced things like crab cakes. Thats where the technology has really made great progress. These proteins are quite a leap from the previous genera-tion.
Sometimes, size factors into the equation. One extruded soy protein yields a larger, more meat-like size that enables food designers to offer a protein-complete meat replacement that more closely matches meats natural fibrous structure, texture and chewing properties, says Werner Barbosa, meat and convenience category marketing manager, Cargill Texturizing Solutions, Wayzata, MN. At 50% protein, the product typically absorbs 2.5 to 3.5 parts water to 1 part textured ingredient, and finds widespread use as a protein replacement for poultry, beef, pork and tuna in soups, stir-fry entrées, meat fillings, pizza toppings and prepared meals, he says. Five minutes in boiling water provides good hydration, and he says the product has excellent freeze/thaw and retort stability.
With textured soy proteins like these, who needs meat?

About the Author(s)

Kimberly Decker

Contributing Editor

Kimberly J. Decker is a Bay Area food writer that has worked in product development for the frozen sector and written about food, nutrition and the culinary arts. Reach her at [email protected]

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