July 1, 1994
All sweeteners are not created equal. Each has particular functional benefits that go well beyond sweetening. In the January, 1992 issue, Food Product Design reviewed the many types of sweetener ingredients and their general properties. This feature will further detail sweetener functionality and how to use functional properties to help assemble a sweetener system that provides specific effects in the finished product.
A foundation in structure
To understand sweetener functionality requires understanding a little about the chemical properties of saccharides. All sweeteners comprise one or more saccharides. Because each saccharide possesses certain properties, the various saccharide combinations found in sweeteners offer diverse functional properties.
"In general, the functional properties come from the saccharide content," says Mark Hanover, director of food ingredient technical service, A.E. Staley, Decatur, IL. "The functional properties are directly related to the chemical structure."
Simple sugars, or monosaccharides, are the building blocks from which all carbohydrates are made. They include dextrose (glucose), fructose (levulose) and galactose. Monosaccharides can combine together chemically to form complex sugars such as disaccharides which consist of two monosaccharides bonded together. The disaccharides most familiar as food ingredients include: lactose (dextrose + galactose), maltose (dextrose + glucose) and, of course, sucrose (dextrose + fructose).
These disaccharides, along with the monosaccharides dextrose and fructose, are all available in high purity crystalline forms for use as food ingredients. As such, their functional properties follow a relatively predictable pattern. On the other hand, corn syrups, malt syrups and alternative sweeteners such as honey are combinations of various mono and disaccharides as well as other components such as polysaccharides and water. Corn syrups, in particular, are challenging to specify because different production methods can give corn syrups different functional compositions even if their dextrose equivalents (D.E.) are identical.
"The D.E. does not tell the story it did 20 years ago," says Larry Hobbs, director of technical services, Cargill Corn Milling, Minneapolis. "Things aren't straightforward with corn syrup production anymore. Acid conversion, enzyme conversion, absorption technology all make the D.E. mean something different."
A high-maltose corn syrup, for example, may have D.E. of 48, but will have a functional performance that is very different from that of a 48 D.E. acid converted corn syrup.
"It's something that the technologist has to be aware of," says Hobbs. "They have to use caution when specifying an ingredient based on D.E."
In addition to carbohydrate sweeteners, designers can achieve specific functional effects with the contributions of polyols, or sugar alcohols. These are made by hydrogenating sugars to convert the reducing end of the molecule to a hydroxyl (-OH) group. Sorbitol, for example, is hydrogenated dextrose. While polyols do retain some of the functional characteristics of their source sugar, the hydrogenation process does cause changes.
"The first way is that they're noncariogenic; the mouth microflora don't really ferment the sugar alcohols," says Laura Przybylski, technical specialist, Roquette America, Inc. Gurnee, IL. "They also don't brown because they don't undergo Maillard browning reactions, nor do they caramelize. So generally they're very heat stable."
Such features are common among the various polyols. With respect to sweetness, freezing point depression, heat of dissolution, etc., however, the individual polyols will vary as do their source sugars.
The functional spectrum
Of all the functional properties sweeteners provide to foods, the most commonly discussed include such things as sweetness, caramelization and texture. What is, perhaps, most important to a sweetener's performance, however, is its solubility. Sweeteners are highly soluble in water and it is this affinity along with their colligative properties in solution which determine a large share of their functional performance.
"If there's a reduced amount of water you will have a generally different rate of chemical reactions, such as browning reactions," says Hanover. "All of this will be affected by the water activity and the water mobility of a system upon which sweeteners have a definite impact."
The strength of a sweetener's affinity for water will be a function of the size and weight of its molecules - lower molecular weight saccharides tend to have a greater affinity for water. For sweeteners such as corn syrup that aren't high-purity single saccharides, the other components also will affect the water affinity. This is one reason the dextrose equivalent isn't as meaningful for sweetener selection as it once was.
"The lower D.E. corn syrup solids tend not to be as hygroscopic as, say, dextrose or 42 D.E. corn syrup," says Dan Putnam, applications scientist, Grain Processing Corp. "However, the long-chain polymers in a low D.E. corn syrup solid can actually help entrap water."
After discussing sweeteners' affinity for water, the first thing that may come to mind is how this attribute contributes to preservation. In foods, water is found in one three form: free and unbound; free, but immobilized; and chemically bound. Extending the shelf life of foods typically requires immobilizing and/or chemically binding the water. Being effective solutes, sweeteners can help achieve both and thus aid in preservation.
Water activity is the equilibrium vapor pressure of water in a food. The lower it is, the greater the degree to which water is chemically bound and unavailable for microbial growth, enzyme activity and other degrading reactions. Sucrose has a relatively small molecular size (molecular weight 342) and is an effective solute for reducing water activity.
Monosaccharides, such as dextrose and fructose, have still smaller molecules (molecular weight 180 for both) and can reduce the water activity to an even greater degree. In certain high sugar products, such as jams and jellies, the osmotic pressure is so great that if certain microorganisms come into contact with the product surface, the water is drawn out of them and they are inactivated.
Again, because corn syrups are made up of a variety of saccharides and other substances, their molecular weights - and, subsequently, their effect on water activity - will vary.
"Corn syrups will have an average molecular weight ranging from that of dextrose to those of certain long chain saccharides," says Hanover. "An intermediate D.E. corn syrup with have a molecular weight similar to that of sucrose. A 50 D.E. corn syrup will contribute properties - osmotic pressure, etc. - similar to sucrose. If you go with a lower D.E. and a higher molecular weight, you'll have lower osmotic pressure. With high D.E. and a lower molecular weight, then you have a correspondingly higher osmotic pressure."
Water mobility, while not contributing to chemical/microbial stability, also is important to preserving quality. The longer chain saccharides of regular corn syrups, for example, don't have the ability to bind water chemically. They can, nevertheless, physically entrap water. This property is useful for adding softness to candies and for long shelf life soft cookies. Immobilizing water also helps reduce ice crystal formation in frozen desserts.
"Unlike fructose and dextrose- the monosaccharides -it's a looser association of water," says Hanover. "Still, it all adds up to a definite effect on the preservation qualities of the food."
Like sugars, the polyols have an affinity for water which varies depending on not only the polyol, but the form of the polyol. Sorbitol, for example acts as a very good humectant in solution, but isn't very hygroscopic in crystalline form. One difference between sorbitol and carbohydrate sweeteners is that it tends to maintain its holding properties rather than giving up moisture as temperature varies.
"Sorbitol is an excellent humectant," says Przybylski. "Other polyols are less hygroscopic. Maltitol is a little less hygroscopic than sucrose, but has similar properties. Mannitol isn't hygroscopic, but it makes a good carrier because it stays dry and flowable."
Ups and downs
The colligative properties of sweeteners don't end with water immobilization and water activity reduction. Also important to the quality of many foods is how sweeteners can depress the freezing point or raise the boiling point of a system.
As is the case with all of sweeteners' colligative properties, the effect increases as the concentration of molecules in solution becomes higher. Again, the effectiveness of the various saccharides improves as the molecular weights become smaller.
Freezing point depression is important for many frozen products, but is especially critical for frozen, dairy-based desserts such as ice cream. As ice cream passes through marketing channels - manufacturer to distribution center to warehouse to grocery store to consumer's home - it has the opportunity to experience many fluctuations in storage temperature. If the freezing point of the product is depressed far enough, seemingly minor elevations in storage temperature can have a profound cumulative effect because the product will pass through several freeze/thaw cycles. Such repeated cycles promote the formation of ice crystals which create a grainy texture in the ice cream and shorten its shelf life. Ideally, a particular freezing point should be targeted that is high enough to minimize the number of freeze/thaw cycles during distribution and the sweetener system designed to achieve it.
Such a balance is especially necessary in low-fat frozen desserts. A frozen dessert base typically requires a level of solids around 35%. Some of these solids are provided by fat which has no effect on the freezing point. Once the fat is reduced, however, a designer might be tempted to reestablish the solids level with a combination of sucrose and corn syrups. While this does build solids, it can lower the freezing point too much. A better choice would be to select maltodextrin (low-D.E. corn syrup solids) because they will help maintain a high solids level without affecting the freezing point.
Again, because they are modified sugar molecules, polyols affect the freezing point much like their corresponding sugars.
"Sorbitol decreases the freezing point more than sucrose, but not enough to make a big difference in texture," says Przybylski. "The resulting improvements in freeze/thaw stability are one reason sorbitol is used in surimi."
Boiling point elevation will primarily affect candies. In hard candies, for example, the required 98% solids to 2% moisture ratio requires cooking to 315°F. Lower molecular weight sweeteners would only increase the cooking temperature. Higher cooking temperatures are not only undesirable from a time and energy standpoint, they can make delivering on the product concept difficult. Caramels, for example, contain milk and other dairy ingredients which have a tendency to scorch. Increasing the boiling point of the system only increases the difficulty of this challenge unless vacuum cooking is employed.
Polyols will tend to hold water more readily than sucrose and, like monosaccharide sweeteners, will increase the cooking temperature.
"Because polyols are heat stable, though, you can cook them 10 to 15 degrees higher than a normal confection," says Przybylski. "But, it won't cause a problem with the confection as far as discoloration.
Moving into macro
With the discussion of sweetener solution behavior over, the focus now broadens to look at the more easily perceived effects that sweeteners have on food systems. Be forewarned, though, the colligative properties of sweeteners may pop up unexpectedly.
Flavor and flavor enhancement. Of all the many functions of sweeteners, they are most known for providing sweetness. Not all sweeteners possess the same degree of sweetness. But, the flavor of sweeteners goes beyond just sweetness.
"Most people don't realize that sucrose has a flavor," says Putnam. "Rock candy, for example, is pure sucrose. It has sweetness, but it also has flavor. Aspartame tastes different from sucrose because it has sweetness, but no flavor."
In premium products, high levels of sweetener are common. Because of the flavor contributions, though, the effect on the finished product might turn out to be negative. At certain levels in a premium vanilla ice cream, the flavor of the sucrose can overpower the creamy, dairy flavors. At the same time, certain products - such as rock candy and donut glazes - a strong sucrose flavor is appropriate.
One way to avoid any overpowering sweetener flavors is to blend different types of sweeteners. Keep in mind, though, that they have flavor contributions of their own. According to Putnam, if the corn syrup solids content in ice cream is over 25%, the taste of the syrup is detectable in the mix. Corn sweeteners can affect the flavor profile in other ways, too.
"Corn syrups can actually mask flavors," says Hanover. "I believe it is caused by the blockage of taste receptor sites due to the long-chain structure of the saccharides."
While flavor masking can be problematic, this quality also can be used to smooth out undesirable harsh flavors such as the vinegar bite in more mildly seasoned salad dressings. On the other hand, certain sweeteners - particularly fructose - rapidly release flavors and fade whereas the flavor of sucrose comes on slower and lasts longer.
"Because of this difference in timing, certain flavors come through better with fructose such as some fruit flavors, some spice flavors and some acid flavors," says Hanover. "Fructose allows these flavors to come through with more impact. I've seen people reduce the acid in their products by as much as 5%."
Keep in mind also that various sweeteners have heats of dissolution that differ from sucrose. Dextrose, in particular, has a significant negative heat of dissolution which can enhance the cooling effects of flavors such as peppermint.
Polyols all have clean, sweet flavors. The degree of sweetness compared with sucrose will vary with the type. Xylitol is the sweetest with about the same as sweetness character as sucrose, while mannitol is 50% as sweet as sucrose.
"Polyols are used where you want the sucrose-like sweetness, but you don't want it as sweet as sugar," says Przybylski. "You get many of the same functional/bulking properties of sugar, but less of the sweetness."
Texturization. Sweeteners not only contribute to a product's texture, they affect how that product maintains its texture. Sweeteners build texture in several ways:
Bulking. In addition to sweetness, the volume of space a sweetener occupies in a product contributes to the fullness and richness of the product. Because different sweeteners have different levels of sweetness intensity, designers can create different levels of richness in a product by balancing different types of sweeteners, or even differently manufactured sweeteners in the same category. This is again related to molecular size.
"If you're talking about a 20 D.E. versus a higher D.E. corn syrup, you're going to get a lot more sweetness in a higher conversion product," says Putnam. "You can't get as much into the formula before you reach or exceed the desired level of sweetness."
The presence of non-saccharide components in lower D.E. corn syrups also will affect the bulking properties.
"All the corn syrups really have an effect on texture, depending on their saccharide distribution," says Hanover. "The higher saccharides of corn syrups makes them more cohesive with longer textures that can give fullness and richness to certain products. The higher D.E. products have a lower amount of these saccharides and have less of an impact in this way. They can, however, contribute to fullness through their water holding capacity."
In yeast-raised bakery foods, sugars compete with gluten for water in the formula. By doing so, they slow the development of the gluten during mixing. This affects the finished product texture by making it more tender.
Body/viscosity. A sweetener's affinity for water also allows it to increase the viscosity of a system - often perceived as body. In the case of corn syrups, their very presence will affect the viscosity of fluid products such as sauces and salad dressings. Yet again, this is related to the saccharide profile of the syrup because lower D.E. products have a greater amount of long-chain saccharides which are good viscosity contributors.
"There are some extremely heavy-bodied syrups in the low D.E. range. When they're cold, you could literally walk on them," says Hanover. "High fructose corn syrup (HFCS), on the other hand, is on the other end of the spectrum. It's a little heavier than water, but even at room temperature is only 1,000 centipoise."
Polyols, for the most part, will build texture similarly to sucrose. This will, however, depend on the polyol being used and how it interacts with water.
"Say you're looking at a baked product," says Przybylski. "While xylitol and maltitol will be like sucrose, sorbitol, being a good humectant, will change the texture and you will see a softening effect because of the moisture. The dough will be stickier and the finished baked product will have a different texture. If you're looking for crispness, that could be a negative effect. If you're looking for softness, it's a positive effect."
Crystal inhibition. The humectant properties of all sweeteners not only control water activity and help build the initial texture, they maintain good eating qualities, too. This function is a combination of softness, water holding and crystal inhibition. This latter function is particularly well-executed by corn sweeteners because their longer-chain saccharides will actually inhibit crystal growth.
"All the corn syrups control crystallization of other sugars," says Hanover. "Some of this is just a physical inhibition of the crystallization process; a certain amount of it has to do with controlling the water mobility."
With respect to the monosaccharide content, crystallization potential is related to dextrose equivalent.
"As you go toward pure dextrose, the greater the potential for crystallization," says Hobbs. "Now, though, there are some very high fructose syrups - products well in the nineties - that are not very crystallizable."
Like sucrose, polyols will crystallize over time depending on the polyol and the temperature to which the product is exposed.
"The temperature of crystallization varies with different polyols," says Przybylski. "It's related to the solubility of the polyol in water. Mannitol isn't very soluble and will tend to crystallize. Sorbitol crystallizes out of a water solution, generally will do so more slowly than sucrose."
Appearance/color. How a product looks is as important as how it tastes and sweetener selection can significantly modify how a product looks. The color a sweetener contributes will be the result of two different thermal reactions.
Caramelization. After passing its melting point, sucrose swiftly decomposes to dextrose and fructosan. These decompose further into a variety of compounds which form caramel. Depending on the degree of decomposition, caramelization can transform sweet, colorless sugars into anything from a pale yellow, mildly caramel-flavored substance to a dark brown burnt-tasting mess. For corn sweeteners, the more converted they are, the more easily they are caramelized and/or scorched.
Obviously, this reaction contributes significantly to the flavor and color of caramel candies and caramel ice cream toppings. It also is important to the flavor and color development of baked products.
Maillard reactions. These reactions do not occur with sucrose because it is a reducing reaction and sucrose is not a reducing sugar.
Dextrose, fructose and others, however, have aldehyde and ketone reducing groups which allow them to react with proteins and amino acids to yield a wide variety of brown-colored reaction products called melanoidins as well as flavorful, odorous volatiles. Maillard reactions form the basis for the flavors, aromas and color of cooked foods. At the same time, however, Maillard reactions aren't appropriate for every product category. In an aseptically packaged, shelf-stable vanilla pudding, for example, crystalline fructose could undergo a Maillard reaction and produce undesirable caramel-like flavor notes. This can be corrected by selecting a different sweetener, or by modifying the formula in other ways.
"pH is a factor in the rate of the browning reaction - 4 to 4.5 is where it happens," says Hanover. "Many products happen to be at pH 4.5 or lower so this will become less of a factor."
Unlike saccharides, polyols neither caramelize, nor undergo Maillard reactions.
Fermentation. Sugars provide food for many biological processes ranging from human metabolism through the commercial production of food ingredients such as lactic acid and citric acid. Product designers will be most familiar with yeast fermentation wherein sugars are converted to alcohol and carbon dioxide gas.
In bakery foods the gas from this reaction acts as a leavener while the alcohol is volatilized off during the baking process. Different strains of yeast are used for beverage fermentation in which, of course, the alcohol is retained and the carbon dioxide sometimes released. No matter what the product, fermentation can be controlled by the amount and type of sweetener used in the formula.
Sucrose is not directly fermentable and must first be broken down into its constituent monosaccharides. In yeast-fermented systems, invertase enzymes naturally present in the yeast will take care of this. The resulting glucose and fructose will tend to be used at different rates. This is why, for example, that residual fructose will be at a higher level in baked products than residual glucose.
Among the monosaccharides, fermentability is yet another quality that is related to the molecular weight: The lower the molecular weight, the easier it is to ferment. For corn sweeteners, this translates into greater fermentability as the dextrose equivalent becomes higher. As has been mentioned previously, though, corn syrups, etc., not only have varying degrees of conversion, but varying proportions of other components. Depending on how they're made, a corn sweetener can actually be designed for a particular fermentation system.
"If you're inoculating the system, the nutrient that you use has to be specific for that particular culture," says Putnam. That would be one reason to use a corn syrup, because they can be fairly specific."
A brewer, for example, may choose to have residual saccharides left for sweetness in a product, or they may want all the sugars to convert to alcohol and carbon dioxide.
"Generally - particularly for high fructose corn syrup - there are certain ingredients used for specific fermentation media," says Hanover. "There are, for example, syrups with specific saccharide profiles that are more compatible with brewing. These allow the brewers to obtain specific alcohol percentages."
Some brewers opt to use sweeteners that are more completely fermentable to give less residual saccharides. This approach is useful when creating light beers because the calorie content is reduced when there are no residual sugars. Reducing the sugar in the finished product is also useful when creating the less sweet "dry" beers.
Fermentation is one area in which polyols differ dramatically from other sweeteners because they are non-fermentable. This is, however, the reason they are noncariogenic since the microflora in the human mouth won't use them, either. Still, polyols could be used to help control a fermentation process while contributing sweetness, but this isn't very common.
Assembling the system
When selecting sweeteners, product designers have to achieve a delicate balance between taste and the many functional properties. This isn't always easy. In ice cream alone, the designer will be trying to control the freezing point, flavor, the total solids content, etc. In many cases, the sweetener that gives the right flavor and solids may alter the freezing point negatively. This is one reason why sweetener blending is becoming increasingly common.
"There is no magic bullet," says Hobbs. "What you gain in one area, you have to sacrifice in another, in terms of functional characteristics."
Hobbs suggests making a list of the effects desired in the finished product and identifying the necessary physical properties. The designer should then prioritize these based on the importance of their contribution to the product. This will then help determine which sweetener's contributions are most critical to the product. With the primary sweetener selected, the designer can then select other sweeteners to fulfill the secondary properties in appropriately lower proportions.
Yes, using sweeteners has come a long way from simply determining how sweet a product will taste. If designers learn how to work with the various functional properties of sweeteners, however, they will find that they have a greater degree of control over the product's appearance, eating quality, shelf life and processability. In the end, this capability can help product designers achieve another sweet taste - the sweet taste of success.
Alternative sweeteners: Fruitful functionality
Although scientific research may indicate otherwise, market research shows that many consumers believe there are benefits from so-called "natural" sweeteners such as honey and fruit juice concentrates. Consequently, designers are required to formulate products with such alternative sweeteners.
This is not much of a challenge when using honey. It is, after all, a fairly standard ingredients composed of approximately 41% fructose, 34% dextrose, 18% water and 2% sucrose. It is similar to, and can used in formulas much like invert sugar. Fruit juice concentrates are a little more challenging for three primary reasons:
Variability. Crops vary from year to year so the fruits available in abundance for fruit juice concentrates will change. If a processor simply stays with the same fruit, the cost can vary widely from year to year. If, on the other hand, that same processor simply chooses the least expensive, highest Brix concentrate available at the time, the finished product itself with vary because the saccharide profiles differ among the various fruits.
Other components. Fruit juice concentrates will possess flavoring compounds characteristic of the source fruit - a problem if the product being designed is not fruit-flavored. For concentrates from certain source fruits, this is true even after extensive purification and decolorization. Still, some nonsaccharide fruit juice concentrate components can actually be beneficial.
"Concentrates serve as a source of minerals not found in other sweeteners," says Scott Summers, manager of technical services for Tree Top, Selah, WA. "They also have naturally occurring fruit acids that can have preserving properties.
Cost. In a perfect product development universe, cost wouldn't be a factor, but it is a reality that real-world product designers must face. The plain truth is that sucrose, high-fructose corn syrup and all the other sweeteners are more economical than using fruit juice concentrate, no matter what the year's crop brings. Still, designers can, at least, formulate with less expensive concentrates. As of this writing, pear concentrates are the least expensive, according to Summers.
Once the decision is made to use a fruit juice concentrate, the actual formulation presents few challenges because they tend to perform like any sweetener with a similar saccharide profile. How much sweetener can he replaced with fruit juice concentrate will depend on the product.
"On yeast doughs, you can replace 4% to 6% of the sugar based on flour weight," says Summers. "In chemically leavened dough we'd usually recommend replacing 25% to 50% of the normal sugar weight. On pie fillings about 8% to 12%."
In addition to calculating how much of the sugar to replace, designers also will have to compensate for the additional water contributed by the concentrate. In general, for every pound of sugar replaced, 1.4 pounds of concentrate should he added and 0.4 pounds of water reduced from the formula.
"When using this replacement, you should make an analysis of flavor and texture," says Summers. "These are guidelines. By no means is sweetening with fruit juice concentrates as simple as replacing the dry sugar and adjusting the water."
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