Putting Proteins to Work
By Kimberly J. Decker
Where would we be without proteins? We certainly wouldn’t be sitting comfortably at a café, enjoying golden-brown muffins and frothy cappuccinos on a sunny morning. Proteins are everywhere.
For one thing, they’re on the cover of best-selling diet books; say what you will about the wisdom of high-protein diets. But fad diets aside, proteins play a crucial role in human health. Our cellular machinery, muscle fibers and even our hair all owe their structure and function to proteins’ power.
Proteins not only make up a big chunk of our own bodies’ structures, but they also do the same in the foods we eat. Take whipped cream, for example — proteins help create and stabilize that characteristic foam. Gelation in sausages results from the action of proteins. And that’s only the beginning.
Protein molecules provide a twist on the usual “form follows function” — with proteins, function follows form. Proteins consist of amino-acid chains linked by peptide bonds into high-molecular-weight compounds. Because of the number, type and charge of the amino acids; the surrounding pH; the presence of other molecules; and other parameters, proteins can take on a number of primary, secondary, tertiary and quaternary structures, each of which affects function.
The primary structure consists of the protein’s chain-like sequence of amino acids, whereas the specific patterns in which the chain’s segments interact with one another constitutes its secondary structure. The entire protein conforms into a specific overall three-dimensional shape, its characteristic tertiary structure. Aggregating several proteins into one larger group produces a quaternary structure. Some examples of these arrangements include the secondary structures known as the α-helix and β-pleated sheet; the fibrous and globular proteins; and the conjugated proteins — associations of amino-acid chains with other compounds, such as fats, carbohydrates and metal ions. These conformations and associations dictate how the molecules behave as ingredients and as the building blocks of life.
That means that with a little protein know-how, and by choosing wisely among the available functional proteins, formulators can boost the nutrition, taste, appearance and performance of products without resorting to expensive and less label-friendly ingredients.
Case for caseins
Bovine milk contains two different main protein categories: caseins, making up 80% of milk’s protein and defined as those proteins that precipitate at 20°C or less and an isoelectric point of pH 4.6; and whey proteins, comprising the remaining 20% and exhibiting relative acid stability and heat sensitivity. Processors separate caseins from whey proteins via two general precipitation methods: acid and enzymatic.
To render acid casein more soluble, processors add sodium hydroxide or calcium hydroxide to a casein solution, then raise the pH, converting it to either a sodium or calcium caseinate. Both are comparatively soluble in the neutral pH range, with sodium caseinate having a slight edge.
Actually, milk has four different types of caseins — as1, as2, b and k — each varying in amino-acid sequence and behavior. All four of these exist in milk in large spherical particles, called casein micelles. But lowering pH breaks the micelles into casein-aggregate precipitates. Treat those aggregates with sodium or calcium hydroxide and they become the soluble caseinates dried to a powder and used in coffee whiteners.
In addition to improved solubility and viscosifying in coffee whiteners, some of caseinates’ functional benefits turn up in, among other products, whipped toppings. “Processors put caseinate in there for two reasons,” says Eric Bastian, director of research and development at Glanbia Ingredients, Richfield, ID. “First of all, they need to emulsify the fat, and then they need to form a stable foam.” Caseins’ bipolar hydrophobic/hydrophilic structure contributes to a stable emulsion and suits them for stabilizing the interface between a topping’s aqueous component and the incorporated air. (It’s important that casein comes from fat-free milk, as the presence of even a little fat can destroy the ability to emulsify and foam.)
In meat products, caseinates’ ability to bind moisture and meat particles contributes a smoother, richer mouthfeel. In bread, they stabilize foam. They form a matrix that traps air and holds it in the loaf once baking’s heat denatures them and makes them rigid, helping create volume and crumb texture. They can add a bit of dairy flavor, too, although Bastian notes that the quality of flavor depends on the processing conditions. For example, heat might lead to cooked, burnt flavors.
Caseinates precipitate around pH 4.6, which makes them less ideal for use in higher-acid products. Product developers should note caseinate/mineral interactions, too — both good and bad. “Milk is an excellent mineral source,” Bastian says, and some of the calcium, phosphorus, magnesium and citrate in milk are chelated to the casein micelles, making milk an ideal nutrition-delivery medium.
However, mineral/caseinate interactions become stumbling blocks when, as Bastian cites, a product developer working with sodium caseinate decides to fortify the product with free, soluble calcium. That calcium causes caseinates to aggregate. Temperature-wise, caseinates are relatively unperturbed by changes. In fact, because casein’s structure is already somewhat denatured, when it’s heated, not much of consequence goes on.
But remember, these caseinates were made using acid-precipitated casein. Enzymatic precipitation doesn’t produce casein ready for conversion to a caseinate. Instead you get cheese; making cheese essentially forms a casein gel.
The way of whey
After cheesemaking, soluble proteins, called “sweet cheese whey,” are drained off. Whey has an isoelectric point around 5.2, but remains dissolved even at that pH. Its solubility as a function of pH is perhaps the signal distinction between it and casein, notes Bastian.
Whey also differs from casein structurally. As individual proteins, whey proteins weigh less than casein proteins and don’t congregate in massive micelles the way caseins do. Instead, whey proteins occur in milk as individual globular proteins, perfectly content to remain in solution. However, their reaction to heat illustrates another dramatic difference. At high temperatures, whey proteins denature, lose their globular structure, aggregate and precipitate out of solution, which causes them to gel.
Individual globular whey proteins can be subdivided into smaller peptide constituents. Among these, α-lactalbumin and β-lactoglobulin constitute the bulk. In even smaller proportion are whey peptides that display beneficial bioactive health effects. These include lactoferrin, an iron-transport protein crucial to delivering the mineral to infants (and used to fortify infant formulas and beverages for the elderly and immunocompromised); glycomacropeptides (GMP), peptides associated with sugars; and immunoglobulins, to help shore up immune systems.
Whey protein concentrate (WPC) or whey protein isolate (WPI) are whey protein’s working forms — usually powders. The main difference between the concentrates and isolates is their protein concentration, but they also differ in how they’re processed and their effectiveness as ingredients.
“Whey protein concentrates are anything that you can manufacture through ultrafiltration (UF)” of the milk’s liquid whey fraction, notes Bastian. “So I can put my whey through the UF process and start to remove lactose, water and minerals,” as well as a little bit of fat that comes through in the whey stream. (The less fat, the better, as fat impairs foaming.)
As the whey fraction passes through an ultrafiltration membrane permeable to lactose, mineral ash and water, the proteins remain on the other side of the membrane as retentate. Depending on the amount of water removed, plenty of lactose is left in the concentrated protein. The lower end of the spectrum sees a WPC of about 34% protein and 50% lactose. Reaching the upper end of the scale — WPCs at around 80% protein and 10% to 15% lactose — requires diafiltration in addition to the ultrafiltration, which Bastian says, “means that I’m adding more water to the retentate side of the membrane to flush out more extensively the minerals and lactose.”
Higher-protein WPCs — at around 80% — may become ingredients in meat products where gelation properties and moisture-binding texturize the meat and improve its mouthfeel. “People from the meat industry who buy whey proteins say, ‘If you can show me a protein that gels well, then it’ll function well in the product,’” says Bastian.
The even more concentrated WPIs (around 87% protein on the lower end) demand a completely different concentration process — or actually, one of two processes. In ion exchange, liquid whey adjusted to a pH above its isoelectric point passes a positively charged resin bead, which traps the negatively charged whey proteins. A minimal amount of charged minerals may catch onto the bead, but the uncharged lactose moves right past. The process leaves concentrated (generally in the upper-80% to lower-90% range) whey proteins.
Ultrafiltration results in WPC products with fairly uniform protein profiles all along the concentration spectrum, but with ion exchange, the respective percentages of b-lactoglobulin, a-lactalbumin, GMP, lactoferrin and immunoglobulins within the WPIs vary widely. b-lactoglobulin occurs at the highest levels, with concentrations of a-lactalbumin and immunoglobulin following closely behind. But GMP, its charge almost the same as that on the resin bead, repels the bead and flows right past. The alteration in profiles affects the proteins functionally and nutritionally. The high content of b-lactoglobulin, an excellent gelling protein, boosts their ability to hold water and form gels. GMP’s presence inhibits gelling, so ion exchange further enhances gelling characteristics in WPIs.
However, GMP shows promise as a bioactive peptide. To reap GMP during WPI production, processors use a microfiltration process that employs a membrane with a much larger pore size than that used in ultrafiltration. All the proteins permeate this membrane while the fat remains as the retentate. This yields a nearly fat-free WPI and one whose protein profile is much more like that of the WPCs, one with high levels of GMP.
How does a product developer know which type of whey protein to choose? It comes down to a product’s functional needs and cost limits. On a purely functional level, isolates and concentrates both are acid-stable and soluble, giving excellent foaming, gelation and emulsification results anywhere along the WPC and WPI spectrum. The specific level of protein depends on the constraints of the application. More protein doesn’t necessarily give better results — it’s almost certain to cost more, though. When searching for strict functionality at a more reasonable cost, it makes sense to use a WPC with the appropriate protein level.
However, “the real beauty of WPIs,” notes Bastian, “is in the nutrition sector. That’s because you’ve got such a high protein level that you can deliver these extremely good-quality proteins, from a nutritional point of view, to people like body builders, sports-nutrition devotees, infants and hospital patients who need a high-protein diet.” In cases where consumers are looking for nutritional bonuses, the market likely will bear the cost of the added value. And WPIs’ higher concentration of bioactive compounds, such as a-lactalbumin, b-lactoglobulin, GMP, lactoferrin and immunoglobulins, provide even more incentive.
But when working with whey proteins, product developers should take care with heat exposure, because high temperatures are a whey protein’s greatest solubility nemesis — and for applications such as sports drinks, bars or sausage products, it’s critical that the proteins remain soluble. However, Bastian mentions that minor tweaking of the mineral balance in whey products can lend them a measure of heat stability above the standard’s, although they’ll never be able to compete with caseinates in that respect. In some cases, partially denatured whey proteins actually create a more functional WPC, since emulsification and water-binding properties increase a bit as the whey proteins heat-denature. Bastian notes examples of partially denatured WPCs with around 34% protein that are so effective at binding moisture and enhancing viscosity that they function as fat replacers. And in baked goods, the heat-induced denaturation of whey proteins is essential to their interactions with starch and gluten to create the baked good’s structure.
Whey products that see too much heat can suffer from burnt-, cooked-flavor defects. Furthermore, hydrogen peroxide, an oxidizing agent sometimes used to control bacteria in whey products, can impact flavor. If the whey proteins themselves oxidize, they may release substances, such as methionine and sulfur-containing compounds, that lead to off-flavors. But careful processing and production should result in mildly flavored, effective, functional and nutritional ingredients.
Not a tough egg to crack
We now go from the cow pasture to the chicken coop: home of egg proteins. Egg proteins can be classified into one of two general categories: the white, or albumin, proteins and the yolk proteins. According to Glenn W. Froning, professor emeritus, University of Nebraska, Lincoln, albumin proteins exhibit some of the most interesting behavior. Here you’ll find: ovalbumin, accounting for 54.0% of the white’s total protein; ovotransferin, which binds metallic ions and occurs at about 12.0%; ovomucoid, present at about 11.0%; ovomucin, 3.5% of the protein and possessing the fibers responsible for egg-white viscosity; egg white lysozyme, which, at 3.4%, lyses bacteria and provides a protective antibacterial shield for the egg; and about 0.5% avidin, a biotin-binding protein that also hampers bacterial growth by making that B vitamin unavailable to bacteria. The remaining proteins include various glycoproteins and vitamin-binding proteins.
These peptides play important roles in the whole egg but also may prove useful individually. Froning mentions efforts to fractionate some of the egg- white proteins; processors have separated lysozyme for use as an antibacterial in pharmaceuticals with cation exchange. As for food applications, adding lysozyme to cheese prevents bowing from excess gas production. Cation exchange can remove avidin, as well. According to Froning, researchers at Nebraska also have worked on removing ovotransferin for potential use as a metal-chelating antioxidant.
However, most product developers work with whole white for foaming, water-binding, gelation and even the inhibition of crystallization in chocolates. Perhaps its most sought-after functionality, foaming gives angel food cakes and meringues a light, airy structure. This mostly relies on the heat-setting proteins ovalbumin and ovotransferin, Froning notes, both of which display the hydrophilic/hydrophobic structure that allows them to stabilize the air/water interface and maintain the foam. Glycoproteins, found in egg white, also act at that interface and provide the foam with some viscosity. Ovomucin plays another role; Froning says that it helps maintain the foam’s volume by forming part of the surface of the stable globule that traps the air. These proteins’ bipolar structure forms a bridge between the hydrophobic and hydrophilic portions of the foam.
The proteins and other constituents in yolk create a similar bridge-like situation. However, this results not in a foam, but rather in emulsification. Mayonnaise is a classic example. Lipoproteins, phospholipids and cholesterol all contribute, but the phospholipids probably account for most of the yolk’s emulsifying ability.
Although emulsification and foaming are similar in some respects, they’re not interchangeable. The yolk proteins bring aqueous solutions in contact with fat during emulsification. However, introducing even a hint of fat into an egg-white foam will upset the proteins’ polarity. This destroys the protein network that sits at the surface between the air and liquid phases and destroys the foam. When the egg industry separates the yolks from the whites, they need to take extra care in creating a clean break; they generally shoot for no more than 0.05% yolk in the whites. “Anything over that and you start seeing a big effect on the foaming properties,” says Froning.
When pasteurizing liquid egg whites — a step necessary to eradicate Salmonella bacteria — and when drying them to a powder, the industry also pays close attention to temperatures, that, through denaturation, can render the whites’ protein structures unsuitable for whipping. Fortunately, the use of hydrogen peroxide can pick up some of the bacteria-fighting slack, allowing processors to subject the whites to less of the potentially damaging heat. Also, whipping enhancers, such as triethycitrate and sodium lauryl sulfate, can add a degree of foaming ability.
Heat isn’t always the enemy when working with egg proteins, though. These proteins, particularly the lipid-rich yolk, enhance viscosity in a number of products, such as salad dressing and even egg noodles. Froning notes that dried whole eggs and dried yolks often show improved viscosifying function over fresh ones because of the effect heat has on the proteins’ structure. (Ironically, freezing also exacerbates their ability to create viscosity.) When using whole eggs in baked goods, protein denaturation creates the structure of the baked product. The white proteins help create a little volume through holding air in a foam, the yolk proteins do their job blending the fat and liquid components of the batter or dough, and when the heat of baking denatures and rigidifies the proteins, the resulting matrix keeps the air trapped and the ingredients stably blended.
Egg whites and yolks are generally sturdy along the range of pH values they normally encounter in applications. According to Froning, a high pH environment actually can boost the ability of egg-white proteins to form gels, which are important as water binders and texture enhancers in meat and seafood products. “A more highly alkaline gel will give you more water-holding capacity than a more acidic gel,” he says. “If people are making a gel for surimi, they may raise the pH to around 9 or so to get a stronger gel with good moisture-binding properties. You can also produce a strong acid one around pH 5, but it’ll have poorer water-holding capacity.”
Solubility can create issues in some products, so the egg industry has created instantized egg proteins through agglomeration, making a particle size that more easily dissolves. But again, processors must not subject the proteins to extreme temperatures during agglomeration, or denaturation will wreak havoc on solubility.
Egg whites and yolks are prone to browning, too. To avoid caramelization that may occur during heat treatment, egg processors supply glucose-free egg products. “If processors are going to dry the egg white,” notes Froning, “they will remove the glucose beforehand, using the glucose-oxidase method or sometimes even a microorganism to ferment the glucose out.” But in an old-fashioned egg wash, color development is the goal. And in egg noodles and egg breads, the characteristic yellow color signals richness. In fact, some poultry farmers feed more xanthophylls to their hens to end up with brighter orange-yellow yolks.
Eggs have complete, high-quality, highly digestible proteins, earning them favor with body builders fond of cracking raw eggs into their drinks. Yolks contain the carotenoid lutein, touted as a potent antioxidant protector of the skin, heart and eyes. Froning sees a day when we may feed laying hens lutein, as we do with xanthophylls, to increase the yolk’s totals of that antioxidant.
Soy to the world
For as long as people have turned to eggs and dairy, the protein in soybeans has served just as many cultures in equally good stead. Today’s product developer accesses the functional proteins in soy via three general product categories: soy flour and grits (50% protein on a moisture-free basis [mfb]); soy protein concentrates (70% protein, mfb); and isolated soy proteins (about 90% protein, mfb). Beyond these, product developers can turn to texturized products and hydrolyzed vegetable proteins (HVPs) — soy proteins hydrolyzed with enzymes and/or acid and heat, used as flavor enhancers in foods.
The soybean itself consists of about 38% protein. According to Russ Egbert, Ph.D., director of protein research applications, Archer Daniels Midland Company (ADM), Decatur, IL, the first step in soy-protein processing involves cracking the beans to remove the hull, and then rolling them into full-fat flakes. “The rolling process disrupts the oil cell, facilitating solvent extraction of the oil,” which is the following step, he explains. After removal of both the oil and solvent, processors dry the flakes to produce defatted soy flakes; these can be ground into powdered soy flour, sized for soy grits or texturized to produce textured (aka structurized) soy protein (TSP). Depending on whether processors subject soy flours and grits to low heat or intense toasting, the end product may retain its enzyme activity or get improved flavor at the expense of enzymatic activity. Finally, removing residual carbohydrates from dried, defatted flakes makes soy protein concentrates and isolates.
Soy flours, notes Cheryl Borders, manager of soyfoods applications, ADM, are the least processed of the soy protein crop, and in addition to providing 50% protein “as-is,” they also contain fiber and a significant amount of soluble carbohydrates that promote growth of such helpful gut flora as Bifidobacteria. But that same fiber and soluble carbohydrate content can promote gassiness.
The next step up, soy protein concentrates, are usually available in textured or powdered forms. Processors typically use aqueous alcohol to remove soluble sugars from defatted soy flakes, resulting in “a protein with low solubility, and a product that can absorb water, but which lacks the ability to gel or emulsify fat,” says Egbert. Given this, traditional, alcohol-washed concentrates often wind up as fortification agents or as raw material for TSP. But functional soy protein concentrates — those that bind water, emulsify fat and form a gel upon heating — result when the alcohol-washed concentrates are heated, homogenized and spray-dried. Alternatively, processors can remove soluble sugars via a water-wash process at low pH, and then neutralize, thermally process, homogenize and spray-dry the resulting concentrate. Now fully functional, these concentrates wind up largely in meat products as water-binders and emulsifiers, as well as in high-fat soups and sauces to aid stabilization.
The functionality of isolated soy proteins — the most highly concentrated protein sources — depends on their process; heat, homogenization and pH all influence the isolate’s functional characteristics. According to Egbert, “isolated proteins are probably the most versatile of the soy proteins, so they find use in a broad range of food products.” Usually spray-dried, their light color and bland flavor enhances that versatility. Isolates’ gelation, emulsification and viscosifying powers make them popular in soy yogurt, for example, which relies on isolates for gelation and viscosity; in cream soups and high-fat sauces, where emulsion stability and a rich texture are paramount; and in processed meats that need the isolates for gelation and emulsification. As for high-protein beverages and infant formulas, isolated soy proteins modified with enzymes to achieve very low viscosity give these beverages the texture that consumers expect. And don’t forget that with protein concentrations topping 86% on as as-is basis, isolates “can contribute to the final protein content of the end product, depending upon the usage level,” notes Borders.
TSPs are produced from soy flour, soy protein concentrate or isolated soy protein. ADM’s TVP® (textured vegetable protein), Egbert notes, “is manufactured through thermoplastic extrusion of soy flour under moist heat and high pressure,” yielding products of many sizes, shapes, colors and flavors, including the popular bacon-flavored TVP. These make economical additions to everything from meat patties, soups and vegetarian meat analogs, to granolas, cereals, protein bars and pet foods. Combining soy proteins with starches and other powdered proteins, such as wheat gluten, produces unique textured products that simulate ground meats, or meat chunks and strips. TSPs can withstand retorting. This comes in handy in canned soups and in the meat substitutes widely sold in cans overseas.
Product developers can find a host of soy-protein products with an array of functional benefits. Isolated soy proteins and functional soy protein concentrates, when used at certain concentrations (usually above 15%, per Egbert), form irreversible gels. All soy proteins bind water and can enhance texture and yield by controlling moisture loss, shrinkage and syneresis. Functional soy protein concentrates and isolated soy proteins are widely relied-upon emulsifiers, and usually are singled out for viscosity modification, with isolates — including enzyme-modified, low-viscosity options — providing the broadest viscosity range.
A number of enzyme-modified isolated soy proteins boast foaming and aeration properties that allow them to replace egg whites in some products; full-fat or refatted soy flours have been used to replace whole-egg powders at levels from about 25% to 50% in baked goods. Also, ongoing research hopes to find a role for isolated soy proteins in film-forming applications. The increased protein, in combination with the presence of reducing sugars, contributes to color development.
Increasingly, soy proteins are earning kudos as all-around healthful foods. Borders emphasizes that “soy proteins are unique because of their high lysine content,” a common limiting essential amino acid in vegetable proteins. “In spite of a slight deficiency of sulfur-containing amino acids — methionine and cystine — the quality of soy proteins compares favorably to that of beef, egg white and casein when evaluated using the Protein Digestibility-Corrected Amino Acid Score, or PDCAAS.”
Scientific evidence points to substances other than soy protein — specifically phytoestrogens, such as soy isoflavones — as responsible for a range of health benefits, including heart-disease prevention and cancer-risk reduction. Researchers still are trying to piece together the mechanisms, but the general explanation for soy’s benefits comes down to simple common sense. Borders reminds us that while heart disease and cancer are the two leading causes of death in the United States, simple dietary changes may go a long way toward prevention. “In general, as standards of living rise, more animal products are consumed, often bringing along an increase in calories, fat and cholesterol — all of which have been implicated in cancer and heart disease.” Incorporating soy into the diet in lieu of animal products reduces the intake of calories, fat and cholesterol, while also increasing the intake of the soy phytochemicals.
Working all this soy protein into products requires some practical consideration. For one thing, soy proteins are not stable in highly acid conditions. Thus, low-pH juice beverages with soy proteins require stabilization, usually a pectin and xanthan gum combination, and homogenization. Product developers of calcium-rich products should bear in mind that soy proteins coagulate and aggregate in the presence of free calcium ions. As for temperature sensitivity, Egbert notes that temperatures below 120&Mac176;F typically don’t affect soy proteins, and that temperatures between 100&Mac176; and 120&Mac176;F have proven most effective in achieving maximum hydration and functionality when hydrating soy proteins for use in liquids. Soy proteins also typically exhibit very good freeze/thaw stability.
Solubility is critical when dealing with soy proteins. While protein solubility plays a lesser role in powdered beverage mixes or nutritional bars, it’s practically essential in obtaining maximum gelation, emulsification, and foaming or whipping from isolated soy proteins and soy protein concentrates. Heat, pH and homogenization all maximize protein solubility. Also, soy proteins generally form colloidal suspensions, which tend toward the opaque.
Egbert also notes a pervasive confusion between solubility and dispersibility: “These terms, at times, are used interchangeably. However this shouldn’t be the case. In general, soy proteins with high solubility have poor dispersibility.” To improve the latter, processors may lower the pH of the finished protein product or apply lecithin to the finished powder. Agglomeration of the protein powder is another, more costly, dispersion-aiding option.
What about that infamous beany flavor — not to mention any grassy, green and cardboard flavors? Many soy protein off-flavors likely result from lipid oxidation. In minimally processed soy flours, the significant quantity of soluble carbohydrate remaining also may contribute to a less-subtle flavor profile. Fortunately, at the levels typically used in baked goods, flours don’t pose much of a flavor hurdle; at higher levels, product developers usually find that stronger spices or flavoring systems can disguise the soy flavor. More highly processed isolates and concentrates have blander profiles, although some processing conditions used to obtain specific functionalities can lead to bitterness and astringency.
Dairy Protein Decisions
As if deciding between WPCs and WPIs weren’t vexing enough, dairy-protein processors also toss milk protein concentrates (MPCs) and milk protein hydrolysates into the mix. MPC production involves running fat-free milk through an ultrafiltration system to concentrate the full complement of milk proteins — whey proteins and caseins. Protein concentrations range from around 40% to 70%, with the casein and whey proteins keeping their percentage ratio at 80:20. MPCs resemble nonfat dry milk (NFDM) in functionality, although they lack the lactose and ash found in the latter. As such, they work in applications similar to those in which you find NFDM, such as yogurt formulas and as protein-fortification agents. When added to liquid nonfat milk, MPCs not only boost the milk’s solids and protein levels, but enhance the texture and dairy flavor, too.
Milk protein hydrolysates result from treating casein and whey proteins with enzymes that hydrolyze the proteins into smaller, more digestible peptides. This has benefits for individuals lacking the endogenous enzymes needed to break down certain dairy proteins. By supplementing snack bars or beverage mixes for people with such digestive disorders with these “predigested” proteins, processors give the individuals a means of obtaining important proteins they otherwise would not be able to digest themselves. “The first thing you’ve got to realize is that any time you hydrolyze protein, you have a huge potential for bitterness,” Bastian cautions, and that provides the major hurdle to successful application of milk protein hydrolysates in foods.
Separating wheat from chaff
Present in wheat flour — and thus in most breads, pastries, noodles and pasta — wheat proteins are probably more common in the typical American diet than soy proteins. According to Clodualdo Maningat, Ph.D., corporate director of research and development and quality control at Midwest Grain Products, Inc. Atchison, KS, the U.S. domestic market has shifted its focus with wheat proteins to one of “value addition” and increased functionality. “In doing so,” he explains, “specialty proteins derived from wheat are currently commercially available, such as wheat protein isolate, textured wheat protein, hydrolyzed wheat protein, wheat gliadin, wheat glutenin and wheat proteins that are highly extensible.”
The concentration of protein in wheat flour itself ranges from 8% to 16%, depending on the class of wheat — soft, hard or durum. The latter is a high-protein wheat (around 14% to 16%). Hard wheat, ground to a coarse particle called farina, has a bit less protein, while soft wheat has characteristically lower protein levels.
The protein in these different wheat types is made up of four separate fractions, all of which differ most markedly in their solubility: albumins at 15%, globulins at 3%, gliadin at 33% and glutenin at 49%. These last two figure prominently in vital wheat gluten, a roughly 75% protein ingredient. The wet processing used to separate the gluten and the starch washes out the albumin and globulin fractions, leaving approximately equal proportions of gliadin and glutenin.
What gives vital wheat gluten its “vital” moniker is its viscoelastic and extensible properties when hydrated. No other protein has this same trait, which allows gluten to form a stable dough with sufficient water-binding and gas-retention capacity. The viscoelasticity owes itself to gluten’s extensive hydrogen and hydrophobic bonding, which itself results from the high proportion in the polypeptide chain of glutamine and other amino acids with non-polar groups. Evidence also indicates that increasing its high molecular-weight glutenin increases baked-good quality.
Processors must beware of high temperatures when harvesting their product. “Given sufficient time of exposure to high temperatures, gluten can lose its viscoelastic properties — in other words, it can become ‘devitalized,’” cautions Maningat. Also, if wet gluten sits for several hours during extraction, proteases from naturally occurring microorganisms hydrolyze the proteins and turn the gluten into a soupy mess. While wheat proteins are thermolabile, they seem to hold up better in frozen applications. Mangingat says that adding vital wheat gluten to frozen doughs prevents the ice-crystal formation that often leads to yeasts’ poor gassing power.
Relative degree of acidity affects gluten properties, as most proteins are soluble at pH levels below 4.0 and above 10.0, but are least soluble in the neutral (6.0 to 7.0) range. Deamidated wheat proteins, on the other hand, dissolve readily under neutral or alkaline conditions, and hydrolyzed wheat proteins exhibit good solubility over the 3.0 to 11.0 pH range. Ion interactions also can affect solubility, viscosity and absorption by neutralizing charges on the proteins and competing for available water.
Processors should have no trouble working wheat gluten as an ingredient into bread, however, for less-dispersible situations, forming coarser protein particles after drying, or instantizing them by spray-coating with emulsifiers, may help smooth things along. “Developments in equipment design, such as in powder dispersers, allow for increasing dispersability of wheat-protein products,” says Maningat.
Fractionation separates the relatively extensible gliadin fraction from the rubbery, more elastic glutenins, each having respective applications in noodles and baked goods. Processors also use extrusion technology to create texturized wheat gluten powders, granules, chips, shredded flakes or chunks. Extrusion-cooked proteins align into a rubbery structure with meat appearance and texture. Wheat proteins can be isolated to around 90% protein, making them excellent binding agents for vegetarian and processed meat products, as well as for pasta. In frozen biscuits, isolated wheat proteins reduce pastiness. However, Maningat stresses that “wheat protein isolates exhibit extensibility, dough-forming ability and adhesiveness which make them behave significantly differently than soy protein isolates.”
Altering wheat proteins’ molecular size can increase their emulsification and foaming properties. Hydrolyzation of wheat proteins with food-grade proteases renders them water-soluble for use in nutritional drinks or as a milk replacer.
While wheat gluten is low in lysine, it’s still a respectable protein-fortification agent, especially when paired with soy, which, while high in lysine, gets a boost in its own meager stores of methionine from gluten. Proline, leucine and glutamine rank in the top three most-abundant amino acids in gluten; high glutamine levels may be appealing because, although it isn’t an essential amino acid, some studies suggest that it is a “conditionally” essential amino acid. “For example,” Maningat says, “when the human body is stressed by heavy exercise — as is the case of athletes or due to surgery, as in hospital patients — the body’s supply of glutamine is depleted.” Enzyme-hydrolyzed wheat proteins are a reliable source of glutamine for specialty beverage and bar formulas.
From animal to vegetable protein, food product designers have many options at their disposal. With each providing a different functionality, nutritional element and overall outcome, a little bit of protein experimentation will make a perfect product.
Kimberly Decker, a California-based technical writer, has a bachelor’s degree in consumer food science with a minor in English from the University of California-Davis. She lives in the San Francisco Bay area, and enjoys cooking and eating food in addition to writing about it.
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