Photo courtesy ARS USDA.
Product developers typically stabilize dairy systems in order to provide thickness, thus increasing viscosity; retard or prevent separation of dispersed components such as cocoa powder, fruit puree, etc; inhibit crystallization; and/or form gels. Food-grade gums are capable of all this, among other functions.
Gums are classified by source, such as seaweed (i.e., alginate and carrageenan), plant seeds (i.e., guar and locust bean), plant extracts and exudates (i.e., pectin), microbial (i.e., xanthan) and various cellulose derivatives. Though most have application in dairy systems, some are more commonly used than others.
Gums belong to the broad ingredient category called hydrocolloids. The primary function of all hydrocolloids is alluded to in its name, where the prefix "hydro" means water and "colloid" means a gelatinous substance. Some hydrocolloids form thermoreversible gels where gelation occurs on cooling or heating. Others form nonthermoreversible gels, also called thermally irreversible gels. And some gums do not form any type of gel at all on their own.
Often used in dairy foods
One of the most commonly used gums in dairy foods, particularly highly viscous cultured products, is locust bean (LBG). LBG is extracted from the seeds of the carob pod, which grows on the carob tree. The seeds contain the highly functional carbohydrate galactomannan, which is what makes LBG such a prized ingredient.Considered an all-natural stabilizer and a source of soluble fiber, this long-chain polysaccharide is capable of binding large amounts of water as it hydrates. Unlike guar gum, also a galactomannan, LBG requires heat in order to fully hydrate. Heating provides the additional energy required to activate the long-chain molecules and allows these molecules to sweep through the surrounding water molecules promoting hydration.
Because LBG only develops viscosity after heating, it is readily dispersible in aqueous systems without excessive viscosity build up. Being non-ionic, LBG is not affected by ionic strength or pH but will degrade at pH extremes at higher temperatures.
In ice cream, LBG, which is hydrophilic, is very effective in preventing syneresis and for controlling the formation of ice crystals as the finished product goes through freeze-thaw cycles. LBG is also often used in dairy systems with other gums for synergistic functionalities. For example, on its own, LBG does not form a gel, but when combined and heated with xanthan gum at a 1:1 ratio, it will form an elastic gel, much like gelatin. The heat provides the energy to promote cross-linking between the xanthan molecules and LBG, thus creating the gel. Typical applications include cream cheese, refrigerated dairy desserts, ice cream and the fruit preps that go into these products. LBG will also form a true gel with kappa-carrageenan. Such synergistic blends are often used in gelled desserts.
Like LBG, xanthan gum is a non-gelling hydrocolloid. However, it does differ in the fact that it hydrates rapidly in cold water to give a reliable viscosity. The consistent water-holding ability may be used for the control of syneresis and to retard ice crystallization. Xanthan gum is often used in ice cream, particularly lower-fat formulations since it functions as a fat substitute by adding the mouthfeel of fat without the calories.
Xanthan develops a very high viscosity, even when very little is used. When mixed with guar gum or LBG, the viscosity is more than when either one is used alone, so less of each can be used.
Guar gum, too, disperses and swells almost completely in cold water to form a highly viscous solution. It has an extremely high water-binding capacity, providing very high viscosity in water-based systems even at low dosage levels.
Powdered guar gum ingredients disperse and hydrate in cold or hot water, with the rate of hydration directly proportional to the water temperature, particle size of the powder and the rate of agitation. Guar gum solutions are thixotropic, which means viscosity reduces as agitation or pressure is increased at a constant temperature, and then returns to the same thickness when it is still. This feature is not too important in the dairy industry, except in the formulation of cheese sauces, dips, dairy-based dressings and spreads.
In cream cheese spreads and some dips, guar gum is often used in combination with LBG. The two have a synergistic effect in keeping water bound. As one cuts through cream cheese or breaks into a dip, some of the hydrated LBG molecules are broken. The guar gum's job is to pick up the water, preventing syneresis.
Carrageenan, which is produced from red seaweed, is available in three different forms: kappa, iota and lambda. All forms must be heated to dissolve. Each form has unique characteristics. For example, kappa-carrageenan forms a gel on cooling in the presence of potassium ions or proteins, whereas iota carrageenan requires the presence of calcium ions to form a gel. Lambda carrageenan is incapable of forming gels, but can be used to control viscosity.
Carrageenan is used in a variety of dairy applications. One of its most common applications is chocolate milk, where it keeps cocoa particles in suspension.
Pectin is derived from the peel of citrus fruits or from apple pomace. The word "pectin" is derived from the Greek word "pektos," which means firm and hard, reflecting the ability of pectin to form gels. Pectin is commonly used in fruit-based products, including fruit preps for yogurt and ice cream. Pectin is also used to adjust the mouthfeel of fruit- and dairy-based beverages and as a protein stabilizer in cultured milk products.
Brown seaweed contains alginic acid, which is the basic raw material used in the production of alginate. One of the most distinctive characteristics of alginate is its ability to form gels in the presence of calcium. Fully gelled alginate systems are neither shear-reversible nor heat-reversible. Alginate is used in fruit preps and a variety of dairy-based desserts.
In nature, cellulose provides structure to plants and their fruits. There are many types of cellulose ingredients, and they vary by functionality, price and application. Carboxymethylcellulose (CMC), also sometimes simply called cellulose gum, is known for providing a wide range of viscosities. Solutions are pseudoplastic, which means viscosity changes when various physical forces are applied. For example, when shear stress is increased, viscosity decreases. This viscosity change is completely and instantly reversible, and the original viscosity is regained when the shear terminates.
Because of this pseudoplastic attribute, viscosity can only be measured for CMC solutions at a defined shear rate. Thus, viscosity for CMC is often discussed in terms of "apparent viscosity," which denotes a definite value only under specified conditions. Pseudplasticity is not to be confused with thixotrophy, where viscosity reversal is time dependant. Some cellulose ingredients, such as microcrystalline cellulose (MCC), are thixotropic in solution.
CMC and MCC are both used in ice cream, where it helps prevent and retard ice crystal growth. In milk and yogurt drinks, cellulose ingredients assist with keeping other ingredients in suspension.
Photo courtesy ARS USDA.
Troubleshooting tips
The most common problem food formulators and manufacturers encounter when working with gum systems is improper hydration. Whenever possible, suppliers advise exposing the gum to water for a sufficient time to allow for initial hydration before acids and salts are added. Other processing conditions such as high temperatures or mechanical stress must be accounted for when selecting a gum usage level.For the most part, gums have a tendency to form lumps, also referred to as fish eyes, when added to water. To prevent this from happening, many suppliers offer hydrated versions of select gums. Though they tend to cost more, and usage levels might be a bit higher, hydrated gums are easier to work with as they eliminate the creation of lumps that can occur when regular gums are added too fast to water.
If you are determined to use regular gums, the best way to prevent lumping is to mix the gum with another dry ingredient that is part of the formula, such as sugar. A ratio of one part gum to 10 parts sugar is often recommended. Then sprinkle this dry blend into water using constant agitation. If another dry ingredient is not available in sufficient quantities, the gum can be mixed into an organic solvent such as soybean oil or propylene glycol, again, if it is part of the formula. To create this slurry, it is often recommended to blend one part gum with five parts organic solvent. This slurry is then blended into rapidly mixing water.
