CHICAGO — Sedimentation, separation, settling and syneresis are some of the many visual stability defects dairy foods may encounter if they are not properly formulated to withstand the rigors of processing and distribution. Unstable systems also reveal themselves through mouthfeel. Expelled water may freeze and form ice crystals in ice cream. Proteins may aggregate around water and form a slimy gel. Milk minerals may interact with other ingredients, producing grittiness.
“Oftentimes a product’s shelf life is determined by physical qualities ahead of product safety defects,” said Donna Klockeman, senior principal food scientist with TIC Gums, White Marsh, Md., a business unit of Ingredion, Inc. “This is to say that when a product’s appearance begins to deteriorate, it is generally before the product is unsafe to eat.”
Thus, stabilizing ingredients prevent product waste by thwarting premature discard of product because of undesirable appearance or mouthfeel. They keep the dairy system in place, or stabilized, through the binding of water. Depending on the product and its composition, moisture management may prevent undesirable ingredient interactions. In other instances, it may keep ingredients in solution. This includes preventing the color of fruit prep from bleeding into the white mass in layered yogurt as well as keeping cocoa particles dispersed in chocolate milk.
Dairy foods stabilizers are either polysaccharides, such as gums, fibers and starches, or proteins, such as whey and gelatin. The presence of hydroxyl (-OH) groups may increase their affinity for binding water molecules, rendering them hydrophilic compounds. In doing so, they produce a dispersion, which is intermediate between a true solution and a suspension. For this reason, they are characterized as hydrocolloids, where the prefix “hydro” means water and “colloid” means a gelatinous substance, inferring that they bind water. Often, blends of hydrocolloids work synergistically to best achieve stability goals in dairy foods.
Thickening and gelling
Hydrocolloids vary in functionality and long-term performance. They disperse in water, and in doing so, thicken the system. The extent of thickening varies by the type of hydrocolloid, its concentration, the food matrix, the pH of the food system and temperature.
Many also form gels. This involves the cross-linking of polymer chains to form a three-dimensional network that traps water within to form a rigid structure that is resistant to flow.
Not all gels are created equal, which is why hydrocolloid use varies by desired end results. For example, some gels, when part of a dairy foods matrix, are chewy while others are creamy. Some may be spreadable while others are brittle. Some will contribute opacity and others remain clear.
Other hydrocolloids form non-thermoreversible gels, also called thermally irreversible gels, and will not liquefy when heated. They may soften or shrink, which also is referred to as retrograde. In other words, the gel remains mostly intact once formed.
In dairy foods, the challenge lies in finding the right balance between the different thickening properties and gelling characteristics. The goal is to bind moisture while delivering desirable mouthfeel and texture.
“Overly stabilized dairy products can be pasty and starchy in the mouth and mask flavors,” said Nesha Zalesny, technical sales manager, Fiberstar Inc., River Falls, Wis. “For yogurts, this means less of that tart bite than is expected.
“Another example is with chocolate ice cream. A good texture will give a clean flavor release while still contributing to the melt characteristics. You want the ice cream to taste like chocolate but also not melt all over the place during the eating experience or develop large ice crystals a day after the carton is opened.”
Selecting the right ingredient
Dairy foods systems often rely on custom ingredient blends to achieve the best stability. There are a number of hydrocolloids that are often part of the blends. For example, xanthan gum, which is produced by microbial fermentation, is a non-gelling hydrocolloid. It hydrates rapidly in cold water to give a reliable viscosity, with a little going a long way. Its consistent water-holding ability makes it an effective tool for controlling syneresis. When used in combination with carrageenan, xanthan contributes synergistically to the formation of a thermoreversible gel, meaning that less carrageenan is required to form the gel.
Xanthan also is often used with locust bean gum, also known as carob bean gum, as it is extracted from the seeds of the carob tree. Dependent upon ratios and application, this synergy produces a range of viscosities and gelling characteristics. It often is used in yogurts. By simply changing the usage rate and ratio, the same yogurt base may be made into a range of varying textures and mouthfeels, from thick and indulgent, to light, almost mousse-like.
Guar gum, also obtained from plant seeds, has an extremely high water-binding capacity, making it useful in cultured dairy applications, such as sour cream and cottage cheese, where standing water is undesirable. It disperses and swells almost completely in cold water to form a highly viscous solution. Like xanthan, it is not self-gelling.
In general, native starches form non-thermoreversible gels and will retrograde over time, which results in syneresis. Hence, historically chemically modified food starches have been used to bind moisture in dairy products, as modification adds stability and resistance to retrogradation and syneresis. With the trend toward cleaner labeling, product formulators are revisiting the use of native starches, in particular those that have been physically modified for improved functionality, as well as fiber food ingredients.
“We offer an all-natural, clean label functional fiber product line derived from orange pulp that can deliver similar functionalities as hydrocolloids in dairy applications with the ability to provide a clean nutritional label,” Ms. Zalesny said. “These functionalities include thickening, emulsifying stabilization, reduced syneresis and fat reduction.”
Gelatin long has been used to provide a melt-in-your-mouth sensation to yogurt, especially in low-fat and nonfat yogurts that lack the creaminess of milkfat. Gelatin is able to absorb 5 to 10 times its weight in cold water. Specifically, with yogurt, gelatin prevents whey from being expelled from the casein gel. This is because the gelatin molecules form a lattice in the casein gel during the gelling process that gets stabilized by hydrogen bonding.
Premium Ingredients, Murcia, Spain, recently introduced a stabilizer system based on dairy proteins that is designed for the production of Greek-style yogurt and Petit-suisse. It was developed with the goal of optimizing the final product in terms of cost, texture, level of protein and syneresis control. The stabilizer blend’s composition, which maintains a casein and whey protein ratio identical to milk, allows its use in a range of fermented dairy products. It ensures a rich and creamy texture, as well as optimal body and mouthfeel.
The system relies on recombination technology, as it produces fermented dairy products without whey drainage, thus obtaining 100% yield. Manufacturers also avoid the costs associated with managing byproducts such as the whey that must be discarded during strained yogurt production.
With frozen desserts, hydrocolloids have a dual function. First, they aid in suspension and help provide emulsion stability to the mix. Then, when the mix gets processed to a frozen state, the hydrocolloids reduce iciness, prevent the development of a coarse texture and bind water during heat-shock cycles.
Gums and starches often are used in ice cream; however, there’s a growing trend to using specialty dairy proteins. The proteins not only bind water to improve product quality, they also boost the nutrition profile.
In the past few years, there’s been a surge of innovation in low-sugar, high-protein ice cream products. The products are packaged in single-serving formats and competing for share of the snacking dollar.
Such systems present a number of stabilizing challenges, mainly from the reduction of sugar solids, which impact freezing temperature. The final product tends to be rock hard. A slight thaw makes it easier to scoop and ice crystals form when it’s returned to the freezer.
“Manufacturers we’ve spoken with say their biggest challenge is coming up with a recipe that yields the desired nutritionals, yet still tastes excellent and also has the right mouthfeel and creamy texture of traditional ice cream,” said Thom King, president and chief executive officer, Steviva Ingredients, Gresham, Ore. “So, we created a low-sugar, high-protein dry mix that gives dairy producers a plug-in solution to take the guesswork out of creating a superior product with fewer than 80 calories per serving.”
The company’s proprietary blend is based on monk fruit extract, stevia, erythritol, milk protein concentrate and hydrocolloids. It enables manufacturers to create a home-style ice cream with a short ingredient list that yields 5 grams of protein and 8 grams of carbohydrates per serving.
Specialty dairy proteins, both casein and whey, are being explored by processors in all dairy applications for their ability to increase protein content while stabilizing systems. This is particularly true in beverages, including refuel milks and meal replacement beverages. An issue that such ready-to-drink dairy protein beverage processors may encounter is age gelation.
“One common quality defect that can severely reduce a protein drink’s shelf life is the tendency of the protein to form an irreversible gel over time,” Ms. Klockeman said. “Product developers are challenged with providing sufficient suspension of the dairy proteins while extending the shelf life of the beverage without the formation of protein gels.
“Some beverage manufacturers report a maximum shelf life of only three months with traditional stabilizers, while our hydrocolloid designed specifically for this purpose enables beverages to remain stable with no signs of age gelation for more than six months.”
In other dairy beverages, most notably chocolate milk, carrageenan long has been the hydrocolloid of choice as it provides optimal suspension of cocoa particles. This is paramount for chocolate milk packaged in clear bottles as the carrageenan prevents solids from separating and settling to the bottom of the container.
Gellan gum is another option. It forms an adjustable gel that aids in suspension and prevention of separation of cocoa particles.