Understanding stabilizer functionality in frozen desserts helps provide insight that can easily be transferred to other foods and beverages.
Stabilizers modify the mobility of water and, thus, affect textural properties (e.g., rheology, uniformity of appearance and mouthfeel); physical functionality (e.g., machinability); and/or physical stability of foods and beverages during manufacturing, distribution and ultimate consumption. Stabilizers manage large amounts of water relative to their own weight. Therefore, they are used at ultra-low levels that do not significantly affect any nutritional property of the food to which they are added.
Terminology and General Function
Stabilizers are also known as hydrocolloid gums, because they form colloidal dispersions in water. Their effects on water mobility are derived from a high molecular weight and complex, highly branched structure. Individual molecules or particulates of any given stabilizer interact with water and change the behavior of that water. Interaction with other food components sometimes increases stabilizer effects.Differences in structure between various stabilizers produce a wide variety of water-management properties. In some cases, the effect is simply one of increasing viscosity. Adding further structural complexity can change the behavior of water from a material that flows normally and easily to behavior where flow occurs only with the application of shear. In the extreme, gels or gel-like structures that maintain shape are formed. This range of rheological effects can produce profound behavioral effects during processing and/or consumption.
Secondary influences that further affect acceptability of any given food or beverage include crystallization of other components of foods (e.g., sugars), flavor release (good or bad), viscosity/thickness and retention of sensory characteristics (texture) through the entire intended shelflife of the food or beverage.
Stabilizers in Frozen Desserts
Considering stabilizer functionality in ice cream and similar frozen desserts, such as sherbets and sorbets, offers insight that can easily be transferred to other foods and beverages.Unlike other foods, ice cream is designed to be manufactured, distributed and consumed in the frozen state. As a result, management of the number and size of ice crystals is a critical element of the perception of both smoothness (a key quality attribute of ice cream) and the coldness that is part of its refreshing appeal. Ice cream's eating quality also includes the perception of body (bite, chew), in which the organization of ice crystals can play an important role. Besides texture, the amount and structure of ice and the number and size of ice crystals in ice cream also directly influence appearance, aroma (modification of chemistry and physics of aromatic components) and taste (sweet, salty, bitter, sour, umami, etc.). Ultimately, all affect the flavor of the finished food.
Stabilizer functionality in ice cream is further complicated by the fact that it is a complex food containing fat, proteins and salts, whose chemical and physical behavior is affected by the amount and physical presence of water/ice. In addition, some of those components combine with the stabilizer ingredients to provide a further influence on water's mobility.
Thus, managing water and its behavior takes on an added dimension in ice cream. As in other foods, the influence of stabilizers on rheology plays an important role in the eating quality related to the perception of creaminess and richness. Beyond that is the maintenance of smoothness by keeping ice crystal size well below the perception threshold by reducing water mobility. Stabilizers minimize the effects of the recrystallization and ripening phenomena that inexorably cause ice crystals to grow. That functionality is a key element of delivering smooth ice cream to the consumer.
Given the low usage level of stabilizers, they play only a minor role in affecting the properties of the liquid mix before freezing. Their primary influence there is to add a small degree of viscosity, with little distinction between the effects of the various stabilizers used. However, when water is frozen into ice, the effective concentration of stabilizer increases, due to the influence of freeze concentration. When water is frozen, it ceases to be a solvent. As a result, the original solutes (sugars, salts, proteins, etc.) and suspended materials (proteins, fat, stabilizers, etc.) are concentrated in the unfrozen water. At very low storage temperatures, 85% or more of the water is frozen, producing as much as a five-fold or greater increase of the concentration of stabilizer in the water of the unfrozen phase. At such levels, stabilizers become highly effective in managing ice-to-water-to-ice transition and water mobility, thus imparting individual gum functionality to the rheology of the unfrozen phase and, therefore, the eating quality of the product.
Popular Stabilizers
A description of some of the most frequently used frozen dessert stabilizers are as follows.- Guar gum and locust bean gum (a.k.a. carob bean gum) are referred to as galactomannans, in that their molecular configuration involves a central backbone of mannose with branched structures made up of galactose units. Differences in the details of that structure account for differences in their functionality. The cryo-gelling capability of locust bean gum helps make it the most effective of stabilizing gums in controlling ice crystal size. In addition, it shows useful degrees of synergism with other stabilizers, such as carrageenan and xanthan gum. Guar gum, while less effective than locust bean gum, is used extensively because of its relatively low cost. The variability in performance between locust bean gum and guar gum is the result of differences in the galactose-to-mannose ratio in their molecular structure–1:2 in guar and 1:4 in locust bean gum.
- Tara gum is another galactomannan that has recently found application in ice cream as a low-cost alternative to locust bean gum. Its galactose-to-mannose ratio is 1:3, which makes it intermediate between locust bean gum and guar gum in its functionality.
- Cellulosic gums represent various modifications of cellulose. The molecular configuration of cellulose involves very long, unbranched chains of dextrose units. It has no intrinsic water-immobilizing effects but can be chemically modified into a branched form that attracts water in a way similar to that of the natural gums. The branches are formed by interacting various organic entities with reactive elements of the dextrose chain. The identity of the specific structures used for the branching gives the names to these materials. Thus, the addition of carboxymethyl groups forms carboxymethyl cellulose, the most commonly used cellulosic gum in ice cream, often referred to as “CMC,” or by the usual name accepted for ingredient labeling — “cellulose gum.” CMC is often preferred because of the desirably chewy body associated with its presence. A broad range of functional CMC properties is possible by controlling the degree of substitution and the length of the cellulose backbone.
Other cellulosic gums have specialized applications in frozen desserts. For example, hydroxypropyl methyl cellulose (HPMC) provides whippability and shape retention properties to water ices and sorbets that are useful in producing extruded forms of those products. Hydroxypropyl cellulose (HPC) provides whippability and water mobility control that shows promise for useful functionality in ice cream.
- Microcrystalline cellulose (cellulose gel, MCC) is a cellulose derivative formed by physically interacting crystalline cellulose with colloids, particularly CMC, to form minute particles that form a gel in water under the influence of shear. The control of water mobility associated with MCC is based on that gel-forming ability, rather than an intimate interaction with water at the molecular level. MCC gels are valuable in ice cream, not only because of the control of water they provide, but because of their foam-stabilizing ability. This makes them useful in maintaining the integrity of small air cells that provide a desirable perception of creaminess and, thus, a fat-sparing effect. MCC is also effective in increasing the amount of air that can be incorporated without imparting a light, fluffy body.
- Carrageenans are extracted from seaweed and are available in several forms that vary in their rheological effects, primarily with regard to the presence or absence of gel-forming capability. In dairy applications, some carrageenans function via an interaction with milk protein that produces very high viscosity or gelling at low carrageenan levels. In ice cream, that interaction also has the desirable effect of protecting the protein system against destabilizing influences to which it is exposed.
- Xanthan gum is a microbial polysaccharide that provides stable rheological properties under a variety of formulation and processing conditions. It has become a useful stabilizer in a broad range of food products, but it is infrequently used in ice cream, primarily due to the availability of more cost-effective options.
- Alginates are salts of alginic acid extracted from kelp, in which variable properties are associated with variable proportions of D-mannuronic and L-guluronic acids. Alginates are widely used in foods. Their rheological effects include the formation of gels in the presence of calcium. The use of sodium alginate in ice cream in the U.S. has declined, but it is still popular in other parts of the world.
- Pectic substances are found in most fruits and vegetables. They vary in the amount and location of methoxy groups on polygalacturonic acid. High- and low-methoxyl pectins are available that differ in their ability to attract, immobilize and eventually gel in the presence of acid, sugar and/or multivalent cations. Typically, pectins can be found in highly sugared, low-pH frozen desserts, such as sherbets, water ices and sorbets.
Protein-based Stabilizers
Gelatin differs from other stabilizer materials in that it is a protein. Amino acids, not simple sugars, are the basic units of its structure. Like other proteins, gelatin owes its functional effects to complexities due to amount, type, arrangement of amino acids and tertiary structure of the protein. It was one of the earliest stabilizers used in ice cream. Its use has declined because of kosher considerations, high cost, special processing requirements and the necessity to age ice cream mix to achieve full functionality. In some food applications, the unique gelling properties of gelatin may be critical to success with no alternatives readily available.Dairy proteins (casein, caseinates, whey proteins and their concentrates), like gelatin, are capable of affecting the mobility of water, but to a lesser degree than that of gelatin and the carbohydrate stabilizers. Nevertheless, they can provide useful effects. In milk, the 20 amino acids available combine to provide a broad range of differing protein chemistries, structures and, therefore, functionalities. Their water interaction effects are enhanced by a slight and controlled degree of denaturation, such as would result from treatment with heat, acid or enzymes. Since those effects are less than those of carbohydrate hydrocolloids or gelatin, they cannot meet the total stabilization requirements of most frozen desserts. If they are used at high levels to enhance their effects, proteins can negatively affect other functional or sensory characteristics, such as flavor release.
Ice structuring proteins are naturally occurring materials that protect living materials from the consequences of exposure to temperatures below the freezing point of fluids in their systems. They do so by achieving a slight reduction in freezing point in a non-colligative manner, and/or controlling size of ice crystals below the lethal level. Their functionality does not have a direct effect on water mobility per se; therefore, they are not stabilizers in the usual sense. However, they show great potential for useful effects in ice cream focused only on control of ice crystal size. Two types show the greatest potential. One is a protein produced by yeast through genetic manipulation modeled after that which occurs in arctic fish. The other is extracted directly from the grass of over-wintering plants such as winter wheat.
Soy, egg and other proteins are not typically used in frozen desserts for a variety of reasons. However, they can generally offer a variety of water-management and even water-binding properties to foods. Of course, this depends on the individual chemistry of the protein and the chemical environment of the application.
Starches and Stabilizer Blends
Starch products are widely used for water control in foods. Native starches from various sources were among the early water-control ingredients used in ice cream. They were supplanted first by gelatin and then by the hydrocolloid gums primarily for reasons related to economy and eating quality. The functional properties of starches have since been expanded considerably by chemical and physical modifications and the development of new varieties of the parent grains. These provide a broad range of effects in a wide variety of food products. Some of these modified starches are now being promoted as alternatives to traditional stabilizers in ice cream.Blends of stabilizers may be considered when individual properties of any one type are not desirable, when unique symbiotic or synergistic properties of any given blend may be needed and/or when cost, availability or both must be considered.
The Bottom Line
Stabilizers function in ice cream in a variety of ways. These functions translate well to other foods and beverages. Consider the following:Since effects vary greatly with the amount, type and composition of stabilizer systems, it is always best to have a specific stabilizer system engineered to match the specific functional need in any given food.
Sidebar: Polydextrose: Becoming a Fiber
FOR MANY INTENTS AND PURPOSES, AN INGREDIENT DOES NOT “EXIST” UNTIL IT CAN BE ANALYTICALLY DETERMINED. TAKE POLYDEXTROSE, FOR EXAMPLE. THIS HIGHLY BRANCHED OLIGOSACCHARIDE IS USED AS A BULKING AGENT AND STABILIZER IN MANY PRODUCTS TO REPLACE THE BULK, WHILE REDUCING THE CALORIC CONTENT OF SUGARS.GENERALLY, IT CONSISTS OF 12 GLUCOSE UNITS RANDOMLY BONDED WITH 1,6 LINKAGES. POLYDEXTROSE HAS NO SWEETENING ABILITY OF ITS OWN. IT IS EXTREMELY WATER-SOLUBLE, BUT MINIMALLY DIGESTED IN THE GASTROINTESTINAL TRACT. ALTHOUGH IT HAS BEEN RECOGNIZED AS A DIETARY FIBER IN JAPAN AND SOME OTHER COUNTRIES FOR SOME TIME, A COMMONLY ACCEPTED ANALYTICAL METHOD TO MEASURE POLYDEXTROSE IN FOODS DID NOT EXIST IN THE U.S. UNTIL RECENTLY (WWW1.DIONEX.COM/EN-US/WEBDOCS/5048_AN147_V19.PDF).
AT THE BEGINNING OF THIS DECADE, A COLLABORATIVE STUDY AMONG SEVERAL RESEARCHERS VALIDATED A NEW PROCEDURE TO MEASURE POLYDEXTROSE CONTENT THAT WAS ACCEPTED BY THE ASSOCIATION OF OFFICIAL ANALYTICAL CHEMISTS (AOAC). IT BECAME AOAC METHOD 2000.11, WHICH, WHEN USED IN CONJUNCTION WITH AOAC ENZYME-GRAVIMETRIC METHODS, ALLOWS FOR THE DETERMINATION OF POLYDEXTROSE AS A DIETARY FIBER.
POLYDEXTROSE HAS FOUND GREAT USE IN FROZEN DAIRY DESSERTS, AS WELL AS IN MANY OTHER APPLICATIONS. IN JUST THE LAST FEW MONTHS, A NUMBER OF NEW POLYDEXTROSE-CONTAINING PRODUCTS HAVE BEEN LAUNCHED, INCLUDING CONFECTIONERY ITEMS, ENGLISH MUFFINS, COOKIES AND A SUGAR REPLACER FOR BAKING AND SNACK BARS; THE LATTER WAS INCLUDED IN KELLOGG'S ALL-BRAN STRAWBERRY DRIZZLE FIBER BAR, A VARIETY PACK OF NABISCO 100 CALORIE PACKS CHEWY GRANOLA BARS AND WEIGHT WATCHERS DOUBLE CHOCOLATE DELIGHT SNACK BARS.
—CLAUDIA D. O’DONNELL, CHIEF EDITOR
Sidebar Two
IN FROZEN DESSERTS, PECTINS GENERALLY ARE FOUND IN HIGHLY SUGARED, LOW-PH FROZEN PRODUCTS SUCH AS SHERBETS, WATER ICES AND SORBETS. HOWEVER, THEIR ABILITY TO GEL IN THE PRESENCE OF ACID, SUGAR AND/OR MULTIVALENT CATIONS MAKES THEM USEFUL IN FRUIT-BASED APPLICATIONS, AS WELL. JELLIES ARE A TRADITIONAL USE, BUT FRUIT-BASED DRINKS ALSO MAY BENEFIT. FOR EXAMPLE, MINTEL'S GNPD REPORTS THAT SOUTH BEACH BEVERAGES’ NEW SOBE ENERGY ESSENTIAL JUICE + ENERGY — FEATURING GRAPE, POMEGRANATE AND RASPBERRY JUICE CONCENTRATE, AS WELL AS CITRIC AND ASCORBIC ACID AND SEVERAL BOTANICAL EXTRACTS — CONTAINS PECTIN.< BR>—PFEDITORSFor more on stabilizers and other technical aspects of ice cream science and technology, join Dr. Bruce Tharp and Dr. Steven Young at “Tharp & Young on Ice Cream Technical Short Course, Workshops, & Clinics,” December 3-5, 2008, Las Vegas. For more information and registration, go to www.onicecream.com or call 610-975-4424 or 281-596-9603.
