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March 26, 2008
Legend has it that the Roman Emperor Nero created the first frozen desserts when he set up a chain of people to deliver snow from the mountains directly to his dining hall for blending with wine and honey. Chinese sweets-seekers blended snow with combinations of fruit juices, fruit pulp and honey. Marco Polo eventually brought these recipes back to Italy from his travels to the Far East. It is believed that Catherine de Medici then brought the frozen delights from Italy to France. By the 17th century, the French were enjoying sorbet, a term derived from the Arabic word arba, pronounced "shar-ba," referring not to a frozen product, but a chilled beverage.
Frozen fruit confections have remained popular through the ages, especially with the focus on fruits healthful properties. Plus, growing demand for convenience and fun has given rise to a niche within the frozen confections arena that is perfect for fruit: frozen novelties. Characterized by ease of consumption and single-serving sizes, novelty items are considered value-added, because of their configuration, taste, appearance and texture, or some combination thereof. These items can deliver even greater added value in the form of reduced-sugar and low-fat versions.
Fruit-based frozen treats come in many shapes, sizes, colors and flavors. At their simplest, there are the "quiescently frozen confections," fruit or fruit-flavored ices, like the popular Popsicle. But sorbet and sherbet also fall into the category. Differences in these products are, however, more than cosmetic or organoleptic.
FDA has distinct guidelines for sherbets, described in Title 21 of the Code of Federal Regulations (CFR), Part 135, Section 140. Sherbets are defined as frozen products containing at least one dairy ingredient at no less than 1% and no more than 2%, with nonfat-milk-derived solids content not less than 1%, and the total milk or milk-derived solids content is not less than 2% and not more than 5% by weight of the finished food. Sherbet characterized by a fruit ingredient has a titratable acidity (as lactic acid) of not less than 0.35%. Fruit sherbets must contain appropriate levels of the designated fruit or fruit juice: 2% for citrus fruits; 6% for berry fruits; and 10% for other fruits (based on finished product weight).
Sorbets, on the other hand, are considered water-ices and are unregulated beyond noting the absence of dairy and egg yolk (21 CFR 135.160).
Another member of the water-ice family is granita. Italian in origin, granita is thought to have been discovered by a sherbet maker who over-iced his product, resulting in a flaky, granular flavored ice. Although sometimes frozen solid for shaving, granita should not be confused with shaved-ice products. Granitas incorporate flavors before freezing. Shaved ice is made by pouring flavor over ice shaved from a frozen block.
That frozen feelin
Fruit- and/or water-based items exhibit a range of textures. Controlling finished-product texture is crucial for a pleasant, appropriate mouthfeel. Ices, as the name suggests, have a hard, icy texture compared to sherbets smooth, creamy texture. Sorbets are in the middle, exhibiting varying degrees of coarseness.
Sherbets texture is, in part, a function of milk or cream. Modifying ices texture is not impossible, though. Slower freezing promotes formation of larger ice crystals, yielding a harder, icier texture. Conversely, more-rapid freezing produces fewer large crystals and a smoother texture. Modern granita obtains its characteristic texture from stirring hourly instead of continuously (as is done for the more-smooth sherbets and sorbets).
Gums are commonly used to control ice-crystal size, stabilize the product during freeze/thaw cycles, provide a softer texture and add suspension. "Gums such as xanthan, guar, konjac and carrageenan are used in conjunction with bulking agents to increase the solids content and control the freezing point," says Aida Prenzo, laboratory director, Gum Technology Corporation, Tucson, AZ. "Fruit sorbets often include blends of natural gums to help provide excellent texture and melting characteristics." Typical usage levels range from 0.2% to 0.4%.
Beyond controlling freezing parameters, gums can maintain finished-products characteristics. Combining locust bean gum and guar gum provides stability during temperature fluctuationsa more-urgent concern for smaller items such as novelties, pops, etc., since small changes in temperature affect them more dramatically.
One commonality among the various frozen confections is sweetness; however, one might take many turns on that road. Bill Shazer, director, dairy laboratory applications, Tate & Lyle, Decatur, IL, suggests product category as a point of departure. "An organic product would utilize evaporated cane juicebasically unrefined sugar," he says. "If the goal is all natural, then youre looking at sucrose."
Increased availability of crystalline fructose has expanded its application in frozen fruit products. "Its a good, clean, sweet flavor that can enhance fruit flavors," says Shazer. "It will provide economic benefits and still allow for all-natural labeling. If the processor is trying to be more economical, they could use a combination of high-fructose corn syrup (HFCS) and sugar."
The level of sugar, solids in particular, affects more than flavor. According to Shazer, a minimum sugar level ensures that freezing is appropriate for processing needs and consumer demands. "You cant achieve it with 100% fruit solids, as it would be very costly, and it wouldnt be sweet enough," he notes. "There is a definite need for sugarssucrose, fructose, the corn syruptype products."
Sweetness is achieved by incorporating a given amount of sweetener(s), which adds a corresponding amount of solidsin frozen desserts, typically 20% to 30% sucrose solids. These solids lower the freezing point of the mixture, known as freezing-point depression. Generally speaking, increasing the number of molecules decreases the freezing point. Higher-weight molecules, however, have a lesser effect on freezing point than lower-weight ones.
"Freezing point depression control is a function of the number average molecular weight (Mn) in solution, and it is a critical factor to consider" when selecting a sweetener system in ice cream and frozen fruit desserts, notes YoungSoo Song, food applications associate project coordinator, Roquette America, Inc., Keokuk, IA. "Freezing-point depression has a direct effect on the overall texture and bulking qualities in ice cream blends," she says. "Excellent texture and taste, as the primary hurdles, are at the top of the list of successful criteria, regardless of the claims that are made with sugar and fat replacement."
Freezing point affects finished product hardness by determining how completely the mix is frozen. At a given freezing point, a product may have some unfrozen water, which is what allows consumers to scoop and chew the product. If it is depressed too low, however, the finished product will be too hard to handle and consume. "The targeted scoopable temperature at which a desirable dipping texture is obtained in ice cream or a frozen dessert system is related to normal home freezers5 to 10°F," says Song.
Freezing point also affects a products ability to withstand heat shock, such as the temperature fluctuations that occur during distribution. Thawing and refreezing promotes increased ice-crystal formation and subsequent grainy texture. A higher freezing temperature provides greater stability to products likely to see such conditions. Developers must also understand how to manipulate the freezing point to meet the demands of their processing systems.
Corn syrups are specified by dextrose equivalent (DE), the number of reducing sugars present after hydrolysis of corn starch into dextrose and dextrins. A DE of 100 indicates pure dextrose. Corn syrups DEs range from 25 to 63. Higher-DE syrups exhibit lower viscosity and greater freezing-point depression. Formulators commonly combine 42 DE corn syrup with sucrose to set freezing point while capitalizing on functionality: the sweetness of sucrose and the viscosity and freezing-point depression of corn syrup.
HFCS contains 42% to 55% fructose (the rest is glucose), which is similar to the 50% fructose, 50% glucose makeup of sucrose. It provides sweetness on par with sucrose at reduced cost, but it is rarely used alone in frozen products, as its effect on freezing-point depression is twice that of sucrose. Combined with other sweeteners, HFCS can complement overall flavor without dramatically reducing the freezing-point temperature.
In no-sugar products, polyols such as sorbitol and lactitol can provide 30% to 100% the sweetness of sucrose. Hydroxyl-group substitution for an aldehyde group gives polyols their sweetness and leaves them only partially metabolized upon consumption. It is this same hydroxyl group that leads to the misnomer "sugar alcohols," despite polyols being neither sugar nor alcohol. Lactitol and maltitol are polyols suited for use in frozen products, as their effect on freezing point, solubility and hygroscopicity is very similar to sucrose.
"The polyols that deliver the closest properties and performance to these sugar-based systems will give the best results," explains Song. "Crystalline maltitol is the most sugar-like bulk sugar replacer available on the market today." However, it does depend on the original sweetener system.
"Crystalline maltitol is the polyol that most closely mimics the freezing-point depression and sweetness characteristics of sucrose," Song continues. "HFCS, on the other hand, contains about half of the molecular weight of sucrose, so has a stronger effect on freezing-point depression. For a direct replacement of HFCS on a one-to-one basis, a lower-molecular-weight polyol-based sweetener system is recommended. For this purpose, the use of sorbitol would be more appropriate. However, an analysis of the different components of the formula should be considered, as other ingredients may be affecting the equivalent freezing depression point of the ice cream blend. Also, since the digestive tolerance of sorbitol is significantly less than that of most other polyols, its use should be minimized."
Quite often, polyols are combined with high-intensity sweeteners to match sugars sweetness levels. One that is frequently used is sucralose, a carbohydrate whose structural changes yield 600 times the sweetness of sugar in a nondigestible form. It delivers a taste profile similar to sugar. "Sucralose also provides a cleaner flavor than other no-calorie sweeteners," says Michelle Schwenk, applications scientist, Tate & Lyle. "The clean flavor works well with fruit flavors."
Some sweeteners exhibit taste synergy. Fructose is about 17% sweeter than sugar. You might expect a 50:50 blend of sugar and fructose to yield 8% to 9% increased sweetness, but it is approximately 28% more sweet. So, adding fructose could reduce sugar by as much as 28%. A "reduced-sugar" claim requires a 25% reduction from the original formulation.
Replacing sweetness is only the beginning. With greater sweetening power comes reduced usage levels. "You have to functionally replace the sugar in those products so that the product still eats the same and freezes the same way it would with sugar," notes Tammy Reinhart, dairy applications scientist, Tate & Lyle.
Maltodextrins often replace necessary solids and provide the bulking and viscosifying characteristics of sugar without affecting flavor. In dairy and non-dairy frozen products, maltodextrins act as cryoprotectants, inhibiting lactose (when present) and water from forming crystals that would create icy texture and poor scoopability. Their high molecular weight means they have little effect on freezing point.
Polydextrose, a digestion-resistant polysaccharide made from glucose, has virtually no sweetness of its own; therefore, it can be used with high-intensity sweeteners, providing bulk to replace the removed sugars. "With an average molecular weight slightly greater than sugar," notes Schwenk, "freezing point depression will be slightly less." Polydextrose is also a prebiotic fermented by "friendly" Lactobacillus and Bifidobacterium bacteria in the gut. Supporting the growth of these bacteria leads to the production of short-chain fatty acids shown to aid in the prevention of colon cancer.
With physical characteristics similar to those of corn syrup, soluble corn fiber can compensate for lost solids with a heat- and acid-stable material that brings beneficial fiber and probiotic effects. "Usage will depend on the processors desired label claim," notes Shazer. "You can achieve a good or excellent source2.5 grams and 5.0 grams of fiber, respectivelywith a physical effect on the product similar to that of a high-DE maltodextrin or a low-DE corn syrup." Soluble corn fibers effect on freezing point, for example, will be similar to that of a 20 to 30 DE corn syrup. And, because soluble corn fiber has functional properties similar to maltodextrin, he suggests replacing a portion of a formulations maltodextrin with it.
With virtually no effects on flavor, clarity or viscosity, soluble corn fiber is an excellent choice for the growing area of so-called combination products. "Were seeing a lot of interest in blending sherbet and frozen yogurt, or ice-cream with a fruit-based sherbet inside, where people can get real fruit with an added benefit of fiber," Reinhart says.
According to Song, Roquette also offers "an advanced fiber-containing bulk sugar-replacement ingredient (that) facilitates the formulation of frozen-fruit-type desserts by delivering desirable physical and sensory properties in only a single mixing step, to give increased fiber, reduced glycemic index and lower calories."
In good taste
Fruit flavor can be derived from a number of sources. Fruit-juice concentrates provide a natural, aqueous flavoring system. Often a measure of quality, fruit juice is used at levels from 10% to 90%. Typical products fall between 25% and 50%.
Actual fruit can be added as a purée or as pieces with varying degrees of pulp and seeds to create a more-authentic-looking product. Formulators should bear in mind that fruits are 80% to 90% water, which dilutes sugars, and will affect sweetness and freezing point. They may add other components, too. And these might vary, depending on the ingredient used. For example, blueberries, a fruit with quickly rising popularity, "contain pectin, and the pectin level can vary with the ripeness of the fruit, with higher levels at an underripe stage," according to Tom Payne, industry consultant for the U. S. Highbush Blueberry Council, Folsom, CA.
As always, the type of fruit follows the trends. Antioxidants are all the rage across the board in foods. "Pomegranate is very strong these days," Reinhart says.
In frozen desserts, flavors balance with sweetness and acidity to create the taste perceived by the consumer. This balance is affected by certain components. Dairy fat and/or protein in a sherbet will tend to mask some flavor. This is not the case, however, for ices and sorbets with no fat or protein.
Some stabilizers can also mask flavor. Despite its higher cost than many alternatives, pectin is a common choice for sorbets and ices where a bright, fruity flavor profile is crucial. Labeling "fruit pectin" lends itself to the ever-increasing number of all-natural products.
Acid is key to the way a frozen fruit products flavor is perceived. However, dairy proteins present the challenge of protecting said proteins from acid denaturation. Milk proteins isoelectric point is 4.6, while fruit preparation pHs can be as low as 3.5. Freezing immediately after fruit addition can help prevent adverse interactions between acid and proteins. Additional precautions include buffering the acid with phosphates or stabilizers, or using a pectin to protect the proteins. Still another option is to allow some denaturation of the proteins, as it can create a slightly creamier texture.
Water ices and other nonprotein applications are free of such concerns. Acids are added to complement the taste of fruit in the system. "Typically, you would use citric acid with citrus fruits, and malic acid with othersgrape or strawberry, for example," says Schwenk. "Acid selection may also relate to flavor release of the acid vs. that of the fruit. Citric acid is an immediate onset, so it will not be competing with the flavors of citrus fruits whose flavor release is later. Sometimes, a blend of citric and malic can give a better flavor profile with high-intensity sweeteners such as sucralose." Generally, however, citrics low cost (relative to other acids) and ease of use make it the primary acidifier in these applications.
As in most industries, convenience is king. Del Monte Foods, San Francisco, recently introduced Del Monte Fruit Chillers, fruit sorbet that can be stored at room temperature. Made with fruit purée, the product freezes overnight to yield a pleasantly soft, scoopable texture. "The costs in terms of manufacture, transportation, freezing and storage are significantly less than that of traditional sorbet products, which need to be kept in frozen state throughout the distribution chain," says Michelle Faist, corporate communications, Del Monte Foods.
MolliCoolz, Redlands, CA, recently announced the application of a stabilizer blend from Cargill Texturizing Solutions, Wayzata, MN, to its cryogenically frozen ice cream and sherbet products, which include tiny beads produced at temperatures far below the products actual freezing point. The stabilizer, a proprietary blend of carob bean gum, guar gum, mono- and diglycerides, sodium alginate, and agar, keeps the beads from fusing together during distribution and storage.
In this market sector, something cool is around every corner.
R. J. Foster is a wordsmith with a B.S. in food science from the University of Wisconsin-Madison and over 15 years of experience in the food industry. He can be reached by e-mail at [email protected].
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