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.
Some hydrocolloids form thermoreversible gels, where gelation occurs after the hydrocolloid dissolves in solution and is cooled. When heat is applied, the gel melts or dissolves. This is best exemplified by gelatin dessert, which melts in the mouth at body temperature. Gelation temperature and melting point vary by hydrocolloid.
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.”