August 1, 1997
Describing maltodextrins, a colleague once commented: "We're not talking rocket science here."
But these deceptively simple compounds are evolving beyond the basics by playing an increasingly important role in the design of food products. In addition to their traditional role as bulking agents and carriers, maltodextrins have taken on roles as fat replacers, nutrition supplements and high-tech film-formers in a multitude of applications.
The U.S. Food and Drug Administration has defined maltodextrins as a "nonsweet nutritive saccharide polymer that consists of D-glucose units linked primarily by (alpha)-1,4 bonds and that has a dextrose equivalent (DE) of less than 20. It is prepared as a white powder or concentrated solution by partial hydrolysis of corn starch or potato starch with safe and suitable acids and enzymes." (21 Code of Federal Regulations Sec. 184.1444.)
The food industry usually refers to corn-based products when referring to maltodextrins. But in addition to the legally defined corn and potato versions, some ingredient manufacturers also produce "maltodextrins" from other starchy sources, such as rice and tapioca. The current labeling status of these products is unresolved, so they might require the term "hydrolyzed ... (starch/source)."
For these non-corn or non-potato products, too, manufacturers typically keep the DE under 20. However, depending on the starting material, these also may contain compounds other than glucose polymers. For example, one rice maltodextrin manufactured from hydrolyzed rice flour starts out with 5% to 7% protein. Another company offers a rice maltodextrin hydrolyzed from mechanically (rather than chemically) derived rice starch, and this ingredient contains approximately 3% protein.
"A rice maltodextrin that contains protein behaves differently from a corn maltodextrin, or even from a rice product manufactured without that protein," says Mohamed Obanni, Ph.D., research manager, California Natural Products, Lathrop, CA. "The protein has some added effects in terms of structure and water-binding."
The chemical structure of maltodextrins falls somewhere between the complex polysaccharide chains of starch and the simpler molecules of corn syrup solids or sugars. They do consist of a mixture of different saccharide polymers by virtue of the hydrolysis process. A starch molecule undergoes enzymatic or acid hydrolysis or a combination of the two. This cleaves the molecule into smaller, random-length chains.
Even those products with the same DE may contain a different distribution of molecules - more medium-range molecules, and fewer larger molecules, for example. The process, its conditions, and the type of starch used as the starting material, affect the exact composition and structure of the resulting chains. This, in turn, affects the functionality.
Most starch consists of two major polymers with different structures. Amylose exhibits mainly a linear structure, consisting of glucose linked by (1-4) bonds, while amylopectin is highly branched. These branches are attached by (1-6) linkages. Starch composition varies with the source. For example, starch from waxy maize consists almost entirely of amylopectin, while common yellow dent has 72%, potato starch about 79%, wheat approximately 72% and tapioca about 17%. Along with some chemical differences, the amylose:amylopectin ratio impacts the properties of the gelatinized forms.
"Because of these differences in properties of various starch sources, maltodextrins from them can be expected to have slightly different characteristics," says Henry Nonaka, manager of technical customer support, Corn Products, Summit-Argo, IL. "If you were to make a maltodextrin from waxy maize, the solubility and solution clarity would be greater than that made from dent corn, especially at low DE, less than 10. This is due to the lack of linear molecules that can reassociate.
"If you were to derive maltodextrin from potato starch - besides a higher amylopectin content - it would have a higher level of phosphate than other starch sources. These properties confer on it some unique attributes, such as the starch doesn't set up into a firm gel. To some extent, potato starch can be viewed as a derivatized starch," he says.
Maltodextrins from sources other than corn might not only exhibit functional differences, they often display other differences, such as flavor. Since they are generally more expensive than corn maltodextrins, any benefits they confer must outweigh the cost. But other considerations besides functionality exist.
"Rice is used in cases where, for reasons of allergy or marketing strategies, people want to use something else," says Joseph Hall, technical sales manager, at California Natural Products. "There are sulfite issues for some products, and that is something often used in processing corn and potato products. It can even be used for rice internationally, so if that's a concern, you have to be careful."
In addition, the process affects the types of molecules that result. In acid hydrolysis, controlling pH, time and temperature influences the outcome.
"We do a very fast hydrolysis; it takes minutes instead of days," says Neil Hammond, director, new product development, Pacific Grain Products, Inc., Woodland, CA. "That gives us several advantages. There is almost no caramelization, no side reactions. Because we use a rice with some amylopectin, we get different functionalities than you would from rice grown in the South."
According to Obanni, rice maltodextrins made from non-chemical (mechanical and enzymatic) processes resist retrogradation to a greater degree.
With enzymatic hydrolysis, process factors come into play, but the specific enzyme used also impacts the end result. For example, alpha-amylase attacks the (1-4) linkages of starch (the main chain of amylopectin or amylose). Other enzymes, such as isoamylase, catalyze the hydrolysis of the (1-6) bonds and act as "debranching" enzymes. In general, acid hydrolysis tends to produce more sugars, such as dextrose and maltose, which means they will promote browning. The acid/enzyme process usually results in a lower dextrose content.
Dealing with DE
By controlling the various factors, manufacturers control the degree of hydrolysis, and obtain a consistent product. Still, most commercial maltodextrins are a mixture of different carbohydrate polymers. The disaccharide profile that is created influences the properties of the maltodextrin. However, maltodextrins are usually classified by DE. The DE offers the food designer a guide to the properties these ingredients exhibit.
"Probably the most important measurement we do is dextrose equivalent," says Tonya Armstrong, applications scientist, Grain Processing Corporation (GPC), Muscatine, IA. "It's a wet-chemistry method that indicates the amount of hydrolysis done on a starch molecule. The analysis is a measurement of the average reducing power compared to a dextrose standard."
DE indicates the degree of polymerization (DP) of the starch molecule - the number of monosaccharide units in the molecules. DE is derived from the formula DE = 100 ÷ DP. The higher the DE, the higher the level of monosaccharides and short chain polymers. Glucose (dextrose) possesses a 100 DE; starch is approximately zero. Because maltodextrins and other hydrolyzed starches consist of a mixture of polymer lengths, the DE is an average value.
"There's a misconception that DE refers to the amount of glucose," notes Hammond. "But what DE is referring to is that glucose at the end of the molecule. So, 5 DE doesn't mean 5% glucose. In a maltodextrin, it may only be one-tenth of that."
Since a maltodextrin with a low DE contains a larger amount of longer straight- and branched-chain units, it tends to exhibit characteristics more in line with those of starch, such as viscosity. As the DE increases and the level of lower molecular weight products increases, the maltodextrin tends to act more like a corn syrup solid. This means that a number of characteristics of maltodextrins are related to the DE.
"For each product, there is going to be a range of DE," observes Armstrong. "For example, a 5 DE maltodextrin generally ranges from 4 to 7 DE; a 10 DE may range from 8 to 12."
Within these ranges, the ingredients will not show significant differences in functionality. Armstrong notes that while it's difficult to find any differences with a small shift in DE, larger differences indicate greatly different polymer lengths. The characteristics of a 5 DE are vastly different from those of an 18 DE. As DE increases, so do the following characteristics:
Browning (due to the increased level of reducing sugars);
As DE decreases, the following characteristics increase:
Prevention of large sugar-crystal formation.
Function follows form
Most commercial maltodextrins are spray-dried and sold as powders, although some liquid maltodextrins are available.
"Nearly all maltodextrins are sold as spray-dried - or spray-dried and agglomerated," notes Nonaka. "There are reasons that this is, in a sense, almost required; the instability in solution to microbial growth, for example. If you buy it as a liquid product in most cases, it's partially formulated - by that I mean that the final use is going to be in a product that requires preservatives or acid in the end product. This way, the preservatives and/or acids can be pre-added to the maltodextrose solution to increase its stability and shelf life."
The spray-drying procedure and one additional process - agglomeration - also influence the characteristics of a particular maltodextrin product. The method and conditions of spray-drying will affect the particle size and shape, and the resulting surface area. Typical bulk densities of standard spray-dried maltodextrins range from approximately 0.45 to 0.65 grams/cc.
"One of the things that occurs as the result of the spray-drying process is that the product tends to be fairly porous; there's a lot of interstitial void volume in spray-dried material," Nonaka explains. "That helps in applications where you are using it as a carrier for flavors or other ingredients, because it gives you a lot of surface area. And since some of that surface area is interstitial, if you get colors and flavors there, they're more protected."
For agglomeration, the surface of the individual particles are moistened to provide tackiness, and processed so they fuse together. The process, along with more details on spray-drying, is explained in "Spray-Drying - Innovative Use of an Old Process" (May 1997 Food Product Design).
Agglomerating the particles reduces the bulk density from approximately 0.05 to 0.30 gram/cc, and increases the particle size. The larger, more porous structure increases the void volume, and creates a lower surface-to-volume ratio. It improves flowability, dispersion and wettability, and also decreases dusting. Tests performed at GPC show that the flowability of agglomerated maltodextrins, measured in cc/seconds, compares to that of sucrose. Standard maltodextrin product would not flow under the same test conditions.
"Everyone uses a different process for agglomeration - some people have continuous agglomerators, some have batch agglomerators - and that will lead to different bulk densities," Armstrong says.
Agglomeration of maltodextrins also provides a means to develop unique ingredients.
"Using fluid-bed technology - a method of agglomeration first used in the pharmaceutical industry - flavors, colors and other functional ingredients can also be incorporated with the bulking-agent matrix development during the agglomeration process taking place in the dryer," says Eugene H. Sander, president, Zumbro Inc., Hayfield, MN. "Colored and/or flavored low-density agglomerates can be generated to match the food item to which they are added. Acids can be sprayed on during the fluid bed process to match or modify the pH of the final solution."
Co-agglomerating other ingredients with maltodextrins helps ensure uniform distribution of small amounts of ingredients in the final mix. It also can modify viscosity, and aid in the effective hydration of gums and other viscosifiers.
"Co-agglomeration also replaces dry-blending of the hydrocolloid gum with a soluble carrier," Sander continues. "Typically, the source carrier disperses more rapidly than the gum, leaving it behind to form fish eyes. Co-agglomerated, both gum and carrier disperse simultaneously."
Maltodextrins act as dispersing aids, flavor carriers, bulking agents, humectants, viscosifiers and other functional ingredients. They can work in a wide variety of applications - from dry mixes to fillings and sauces to beverages. Due to their osmolality, they can be a valuable source of nutritive carbohydrates.
The functional characteristics related to DE help determine the applications where maltodextrins are used.
"There are two ways of looking at using maltodextrins," says Nonaka. "One is in a liquid system and the other is in a dry. There are different types of functionalities you are looking for in each of these systems."
For example, bulk density is extremely important in a dry mix. In a liquid, the major consideration might be solubility or viscosity. For a powdered drink mix, these all become critical. Each application has its own requirements.
Because maltodextrins fall in the lower DE range, they supply little or no sweetness. They are fairly bland, although they sometimes provide a low level of flavor. They are relatively inert to heat, pH and other process conditions, such as shear.
Maltodextrins aid in moisture control. Soluble sugar molecules with a low molecular weight lower water activity and considerably depress freezing points. The higher molecular-weight chains - represented by the low DE maltodextrins - bind water and add solids without these effects. In addition, some of the long-chain polymers do not dissolve, and may actually physically bind water by forming a gel. Since these do not go into solution, they appear cloudy. As mentioned, the degree of these characteristics depends on the product's DE. However, during storage, maltodextrins, like starch, will retrograde, releasing water and resulting in syneresis.
These ingredients contribute to viscosity by adding solids, and in some cases, especially with lower DE products, by forming a gel. They also can absorb oils in non-aqueous systems.
As mentioned, these properties vary, depending on the type of maltodextrin used. For example, a rice maltodextrin derived from amylopectin-containing rice flour gives a creamy texture and opaque appearance.
"Many people look at a rice maltodextrin, and think that it will act like a corn maltodextrin, but it really doesn't," Hammond says. "In a product like a sauce, or in a pudding, you get a much smoother, creamier texture. The protein can also give some additional functionality to the maltodextrins."
Carriers and bulking
The bland flavor and inert character of maltodextrins have historically given them a significant presence as an economical carrier or bulking agent. They act as an extender for more expensive ingredients, and as a diluent for microingredients, so they may be more accurately handled and packaged. Mixing maltodextrins with gums and other hydrocolloids aids in dispersion, wetting without clumping, and proper hydration.
They are particularly valuable in the flavor industry, where they supply a matrix for spray-drying or plating oil-based flavors or emulsions. Maltodextrins allow these liquids to be converted into a free-flowing powder without changing or masking the flavor.
In plating, oil-based ingredients are coated on the surface of the maltodextrin particle by using a fine spray. This process can be used for flavors or to help distribute small quantities of oil in products like coffee whiteners.
"If you are plating flavors, you may want a large particle size," Armstrong says. "It's not going to be as easy to blend as a spray-dried flavor, and you want as much surface as possible to plate on so the product remains free-flowing. Agglomerated products would give you a more irregular surface, which can help in a plating application."
Maltodextrins are ideal for spray-drying applications, because the high solubility allows a high level to be incorporated into the dryer feed solution, therefore requiring less water removal. In addition, because of their low hygroscopicity, the products are more easily dried.
"The typical DE that is used for spray-drying and agglomeration is 10 or 15," Armstrong says. "It's less hygroscopic than higher DEs because it has a little longer chain length. It's high glass transition temperature provides good product stability."
Often, a maltodextrin is used in combination with gum arabic and modified starch, especially for spray-drying/encapsulation of high-oil products. For these, Armstrong recommends a lipophilic starch or gum arabic that has an affinity for both oil and water. "It helps emulsify the oil, while the maltodextrin aids in encapsulation and drying."
Spray-drying flavors not only turns liquids into solids, it provides some protection to the flavors themselves. Some of this occurs in normal spray-drying operations when the flavor is partially surrounded by the maltodextrin matrix. However, maltodextrins often are used in true encapsulation systems by taking advantage of their film-forming characteristics to form a protective coating for flavors and other sensitive ingredients. In this month's cover story, "Getting a Reaction: The Complex World of Flavors," we discuss flavor encapsulation in greater depth. Since the encapsulant is a carbohydrate, the release mechanism is moisture, so it would only protect the encapsulate in dry mixes.
"The reason that maltodextrins work well in this application is their film-forming properties," Nonaka says. "You need it to form a cohesive film around the material you are trying to protect. Also, the ability for maltodextrins to efficiently encapsulate a material can sometimes be determined by how well it emulsifies the product. What you are really doing is emulsifying the mixture, then spray-drying it."
Maltodextrins also can be used as a bulking agent for a wide variety of dry mixes. As with flavors, they allow more even dispersion of microingredients, such as flavors, colors and vitamins. Products used for this application require certain attributes. In most cases, the finished product needs to be a free-flowing powder. Low DE maltodextrins maintain this characteristic even when allowed to equilibrate at a relative humidity of almost 70%. A 20 DE maltodextrin will form a solid cake at this point.
"The higher the DE, the stickier the maltodextrin will be, and this can be a factor in dry mixes. Bulk density is also very important in this area," Armstrong says. "You want to match the bulk density of the maltodextrin with that of the other ingredients, because you don't want segregation of the dry blend mixture."
In higher moisture, fat-reduced food systems - such as meats, dressings, sauces, and bakery and dairy products - maltodextrins provide some of the characteristics of fat. They retain moisture, and add viscosity and texture, without contributing sweetness. By increasing viscosity, they improve mouthfeel, and aid in aeration for baked goods and frozen desserts. Because they have a low reducing-sugar content, they can be used in high-temperature applications, where excessive browning from caramelization, or the Maillard reaction from higher DE carbohydrates, would be undesirable.
Maltodextrins and maltodextrin-based fat-replacement systems can replace 9 kcal/gram fats in an aqueous system by forming a carbohydrate and water gel that, on a weight basis (depending on the exact carbohydrate:water ratio), only contributes 1 kcal/gram. Depending on the ingredient used, these gels typically contain 15% to 40% maltodextrin. The maltodextrin can be added directly to a formulation, or first mixed with water, if required for a particular application. The texture of the gel tends toward short and creamy. And, when used in conjunction with gums, they can reduce stringiness in the finished product.
Some of the same characteristics can be used in full-fat products, offering the following advantages: controlling viscosity and texture; sparing of more expensive stabilizers; and improving cling and similar functions.
"You can use maltodextrins, in combination with other stabilizers, and it will improve the stability of the system," Armstrong says. "Maltodextrins complement other stabilizers and can often be synergistic with starches and gums."
Low-moisture products, such as peanut butter, cheese or fat-based fillings, also can utilize maltodextrins to replace solids when fat is removed. The particle size should be very fine in these applications, or it will promote a gritty mouthfeel.
Maltodextrins act as cryoprotectants in frozen products and desserts. Because of their higher molecular weight, they do not lower the freezing point as much as sugars on an equivalent weight basis.
For ice cream and other frozen desserts, a decrease in freezing point can result in several negative effects. A lower melt point imparts an undesirable icy mouthfeel and makes the product difficult to scoop; it also negatively affects aeration and requires more energy to freeze solidly.
Maltodextrins also inhibit lactose and ice-crystal formation and prevent the resultant graininess and loss of quality. They help improve the melt characteristics of the product.
Sports and nutrition
For sports, infant and medical beverages - such as oral rehydration and low-residue liquid feeding products - maltodextrins provide complex carbohydrates and allow the formulation of a product that matches the osmolality of bodily fluids (280 to 300 mOsm/Kg). This can eliminate cramping and other undesirable side effects caused by rehydration with water.
To provide a balance of caloric concentration and osmolality, maltodextrins can be used as part of the carbohydrate source. The lower DE/higher molecular weight products provide lower osmolality on a weight basis than sugars, such as dextrose, fructose or glucose. If the goal is to deliver a certain level of calories, much higher levels of maltodextrins can be used, while still maintaining the body's osmotic balance. Because maltodextrins do not contribute sweetness, they are typically combined with sugars for flavor.
"In most sports beverages, you balance the sweeteners, such as fructose, sucrose and dextrose, with maltodextrins to try and optimize the carbohydrate profile and osmolality," Armstrong says. "If you just added maltodextrins, even an 18 DE, it would only be slightly sweet, but not as sweet as you'd want it to be. If you used only other sweeteners, such as fructose or sucrose, at the same level as the maltodextrins, it would probably be too sweet, and the osmolality would be too high."
Maltodextrins can help out in the process, too. "For liquid beverages, you normally want to preblend some of the gums and other hard-to-disperse ingredients, such as vitamins, with maltodextrin," Armstrong recommends.
Some old, some new
In addition to these general application categories, maltodextrins find use in more specific applications. For example, they can be used for a number of different confectionery products: as a binder in tablets, a drying agent and binder in pan coating. Adding maltodextrins to candy can help modify sugar crystallization and prevent sugar bloom. In soft confections, such as fruit rolls, they can act as a humectant and increase flexibility.
When added to extruded snacks, they contribute lubricity and help control expansion. They can serve as binders for seasonings and coatings for nuts, breakfast cereals or snacks, especially nonfried.
"Maltodextrins act as secondary film-formers when used in combination with starches and gums," Armstrong says. "They've been used as coatings for candies or on pizza crusts, where they act as a moisture barrier between the crust and the sauce to resist moisture migration. The lower DE products will be better film-formers, but if you are looking for clarity and sheen, like for a cereal coating, a 15 or 18 DE will provide that."
Maltodextrins have been approved by the U.S. Department of Agriculture for use in meat products as binders. They absorb excess water and reduce purge during storage.
The film-forming characteristics of maltodextrins can improve the adherence of icings to baked products, without increasing sweetness.
While most of these ingredients may not be subject to sophisticated processing to enhance these properties, it's not beyond the realm of possibility. Princeton, NJ-based Avebe America, Inc. offers potato maltodextrins that have long been a staple for fat-replacement applications.
Many food companies are seeking maltodextrins or maltodextrin-based ingredients that perform a specific function - fat replacement in a specific application, solubility under certain conditions, for example. These almost certainly will require new technologies to develop ingredients that meet these needs.
Other manufacturers are looking at different raw material sources and trying to discover if these have applications or functional characteristics that are different and more valuable than the norm. In the future, scientists may manipulate the hydrolysis to obtain certain carbohydrate profiles that provide specific benefits to food designers.
Another possibility is using different raw materials, such as modified starches. No one is currently doing this because it drives costs up. "Would we get some unique products from that?" questions Nonaka. "That could well be. There are a lot of modified starches out there, and it could be technically very interesting to see what happens, but you would have to be able to recover the added cost."
While high-tech maltodextrins might not be practical, or even technically feasible, at this time, why not in the future? After all, if rocket science can put robots on Mars, food science can improve the simple maltodextrin.
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