Proteins provide texture in an abundance of ways. Eggs, which are 90% protein, have been a traditional source for emulsifying, gelling and thickening properties, although these attributes also can be achieved with milk, meat, wheat and soy proteins.
Aside from providing nutritional advantages--such as natural fortification, the presence of branch-chain amino acids and improving heart health--soy, dairy and cereal proteins also can contribute to a cleaner label, and enhance natural flavor and texture.
It has been discovered that without the sequestering abilities of milk proteins like casein, calcium is not very soluble in other beverages. In orange juice, calcium phosphate or calcium carbonate tends to form large aggregates that drop to the bottom of the container and never are fully stabilized in the product, says Lloyd Metzger, an assistant professor in the Food Science and Nutrition Department at the University of Minnesota (St. Paul).
Wheat is the most widely used cereal protein. Gluten, a component of wheat, is a cereal protein that is both extensible and elastic, and gives bakery products their unique properties. Some wheat flour referred to as soft wheat flour is better suited for soft-texture baked goods like cakes, whereas hard wheat flour is perfect for bagels, pasta and other products that have a chewy texture.
Soft wheat flour has a low protein level of about 8% and, therefore, a softer crumb, while breads and pastas have 12% and 15% protein, respectively. To achieve textures between cake soft and pizza dough elastic, the amino acid cysteine can be used as a dough softener that eliminates cross-links by reducing the sulfhydride groups between and within proteins.
Soy proteins do not have gluten and, therefore, require additives if they are to be used in dough for bread and other baked goods. Soy protein is capable of binding water and fat, and has a strong interaction with flavors. Full-fat soy flour that has been activated by the enzyme lipoxygenase can cause a “beany” flavor that is often undesirable.
In beverages, the solubility of proteins and their functionality is based on numerous factors including protein structure, pH, ionic structure and salt content. Salts compete with protein for water. In the absence of salt or at low concentrations, there is reduced interaction between oppositely charged proteins. At high concentrations, proteins tend to stick together or agglomerate, and protein solubility decreases. The pre- cipitation that occurs is called “salting out.”
Swelling and Gelling
A gel is a continuous three-dimensional, solid-like, cross-linked network of protein molecules embedded in an aqueous solvent. Yogurt, hot dogs, cheese and custards benefit from gel formations. Protein gelation often is a result of the application of heat or mechanical mixing, which can denature proteins. Additionally, other food ingredients can influence the temperature of denaturation; as an example, “the addition of sugar can increase the denaturation temperature,” says Metzger.Proteins typically are not identified as thickening agents. However, some proteins (like gelatin) can mimic thickening properties. Gelatin is produced by hot water extraction from beef hide, bones or pork skin. “Gelatin is effective for thickening in that it provides a nice, clean mouthfeel due to the melting temperature,” states David Poppen, technical service manager at a gelatin supplier. It has a relatively low viscosity at elevated processing temperatures. This low viscosity also allows efficient heat transfer in heat exchangers.
Relative to most other gelling agents, gelatin is unique in that it has an elastic texture. There are two types of gelatin, Type A and B, and they perform differently in various applications. The two types of gelatin have a range of isoelectric points (IEP--the pH at which the charge of the protein changes and becomes neutral). The IEP for Type A gelatin is between 7-9. Below pH 8, Type A gelatin is positively charged. Above pH 8, it is negatively charged. The isoelectric point of Type B is in a pH range of 4.5-5.5. These different charges affect how the gelatin will perform in a food application system.
“It is better to work with a product at a point well away from its isoelectric point,” suggests Poppen. Proteins have the least functionality when nearest their isoelectric point. Their viscosity and gel strength drop quite a bit at the isoelectric point.
Manipulating the pH and ionic strength can affect flavor, translucency and gel strength. If, for example, a manufacturer wants a more acidic flavor while formulating a gummy bear, the addition of an acid buffer would meet the requirements. Adding an alkaline buffer like sodium citrate would help maintain a higher pH for a given acid level.
Protein-based gels can be either translucent or turbid. A turbid or cloudy gel is created by first formulating the pH close to its isoelectric point and then heating the solution, whereas clear gels are formed by moving the pH far away from the isoelectric point prior to heating.
Unlike most polysaccharide gelling agents, gelatin gel formation does not require the presence of other reagents such as sucrose, salts and divalent cations. “Gelatin can also provide a variety of textures by varying the bloom (gel) strength or concentration of the gelatin in the product,” says Poppen.
This is because these gums and starches are difficult to solubilize and have melting temperatures much higher than the body temperature. The only way the gums are broken down is via the chewing process. “Thermally reversible gels will maintain a solid structure at room temperature, but melt in the mouth or when heated,” says Poppen.
Thermally reversible gels are desirable because they minimally impact the system's viscosity; they make great stabilizers for sauces in frozen vegetables. “Gelatin enables the manufacturer to eliminate a separate sauce packet in the vegetables by creating stable 'sauce gels' that can be uniformly distributed with the vegetables,” advises Poppen. “These gels melt when the product is heated in a skillet and have low viscosity at elevated temperatures, which results in a sauce with a desirable consistency.”
All Yolked Up
Egg yolk proteins are commonly used to emulsify salad dressings and sauces. More recently, food formulators are using other proteins as egg protein replacers. Proteins have both hydrophobic and hydrophilic areas, allowing them to maintain both oil-in-water and water-in-oil solutions. They are used widely as emulsion stabilizers and texturizers in low-fat butters and margarine products.“Milk proteins and soy proteins have a lot of similarities, but they each have the area where they excel most,” says Carol Lowry, senior applications scientist at a soy supplier. “The emulsifying properties of caseinate and soy are most useful. Both can emulsify oil in the liquid slurry of dried coffee creamers and help emulsify oils in neutral pH beverages.” She notes that whey protein is acid-stable, and using pectin to protect the protein is not necessary (as is the case with soy or caseinate). Combinations of whey, caseinate and soy could be more suitable than any one protein alone to achieve desired viscosity, flavor and mouthfeel, she offers.
“Soy and caseinates take care of any viscosifying that's needed in high protein beverages,” informs Lowry. “However, when a gum system is needed to help suspend particles such as cocoa or calcium, synergies with protein and gum stabilizers are achieved upon trial and error,” she says. “Sometimes, the hydrocolloid can de-stabilize the protein, and you end up worse than you started.”
Proteins stabilize products by preventing syneresis, exudation and separation of whey proteins. They can be used as ideal stabilizers for dairy products such as yogurts and dairy desserts. Gelatin can absorb up to 10 times its weight in water. In dairy products, gelatin can be used to prevent syneresis by binding water, and it provides a surface sheen such as is seen in yogurt. It also can be used as a glaze in baked goods. “Due to their unique fat-like melting properties, gelatins provide sensory properties similar to full-fat products,” says Poppen.
Proteins have water-binding properties that prevent water from evaporating and condensing on packaging material. Additionally, gelatin's ability to protect colloids inhibits the growth of sugar crystals and prevents the formation of a hard, gritty texture and a poor “mouthfeel.” Synergies between certain proteins and hydrocolloids often are used to increase solubility and stabilize viscosity.
Get into 'Foam'ation
Aside from their gelation and thickening properties, most proteins act as an aeration agent by incorporating air into the system. “Gelatin is a great aerating agent and helps produce stable foams,” says Poppen. “In syrup solutions, gelatin reduces surface tension, enabling a higher whip (i.e., allowing more air to be incorporated into the solution).” Gelatins also stabilize foams and, in the case of marshmallows, prevent shrinking during storage.Foaming can result when ovalbumin, a protein in egg white, is denatured while being folded or beaten. “The aeration process incorporates air using proteins to modify texture, making it easier to chew and giving it a lighter, fluffier texture,” explains Doug Rector, group leader of texture systems at a soy protein supplier. The oxidized sulfhydride group of older egg whites changes the level of cross-linking, increasing the denaturation temperature and making highly stable foams. Soy protein can substitute for egg products and act as an exceptional air encapsulate in whipped products, says Lowry
Determining the appropriate protein source for an application is the most difficult part of the formulation process. Regardless of the source, manufacturers can be assured that when an application requires foaming, gelling, thickening or emulsification, there is a protein available that will inspire absolute confidence.
Sidebar: R&D Conference Highlights Protein Functionality in Beverages
The benefits and challenges of dairy and soy proteins will be addressed at Prepared Foods' R&D Conference to be held on Sept 19-20, 2005, at the Marriott in Oak Brook, Ill.“The Health and Nutrition Role of Dairy Proteins,” “Usage and Functionality of Soy Proteins in Beverage Systems” and “Whey Protein in Beverages” are only a few of the sessions designated to highlight the benefits and challenges surrounding the functionality of proteins.
Soy and whey proteins have been very influential in increasing the nutritional profile of beverages. Proteins are extremely important to beverage systems, but play a precarious role in thickening and stabilization. If the protein content is not well balanced, manufacturers run the risk that proteins will precipitate out of solution.
There are several different techniques that can be applied to minimize sedimentation of protein in beverages. The topics listed below will be discussed in detail at the conference in September. For more information about the conference schedule and the featured topics, visit www.PreparedFoods.com and enter “R&D Conference” in the LINX search field.
pH
Solubility is very dependent upon pH. Whey proteins will remain soluble at pH 4.5 in acidic beverages. Soy proteins also can be successfully formulated into a number of beverage systems, including dry blended beverages, and ready-to-drink acidic and neutral beverages.
Temperature
Heating most proteins will decrease their solubility. Processes such as spray-drying and pasteurization, if done incorrectly, can influence a beverages' solubility.
Protein and Gum Interactions
Hydrocolloids influence the viscosity of proteins by reducing the appearance of serum phase separation. Certain gums can form a pourable gel network that suspends proteins, flavor components and other particles.
Flavor
Some manufacturers are cautious about using certain proteins due to inconsistencies between the application and the protein's natural flavor profile. Advances in flavor and application technologies to help formulators develop great-tasting beverages are becoming a reality at many companies.
