October 1, 2007
The average consumer, seeing natural on food labels, perceives it as a positive factor, mainly because it is typically associated with food safety and significant health benefits. In formulating natural food products, gums and starches isolated from plant sources are widely used as stabilizers.
Chemical modification of gums and starches is widely performed to improve functionality and enhance stabilizing properties. However, the modified compounds can no longer be claimed as natural. U.S. definitions of the term are sketchy, especially as applied to stabilizers, but USDAs Food Safety and Inspection Service (FSIS) requires the following for natural products: It cannot contain any artificial flavor or flavoring, coloring agent, or chemical preservative or any other artificial or synthetic ingredient. The product and its ingredients are not more than minimally processed. The policy also refers to the National Organic Program for acceptable ingredients allowed for all natural claims.
Natural gums and starches are not chemically modi- fied, just isolated from the plant to obtain a concentrated, more commercially viable food ingredient. For centuries, we have derived hydrocolloids from products biosynthesized naturally by plants. Typically, after isolating and elucidating the chemical structure of specific components, such as alkaloids, colors and flavoring agents, from the natural source, processors develop methods to synthesize chemically identical compounds in vitro. However, for starch and gum polysaccharides, it is more economical to isolate and purify the high-molecular-weight polymers from the original plant sources made available to man by Mother Nature typically from plants and seaweeds.
Hydrocolloids, commonly known as water-soluble gums and starches, are high-molecular-weight plant polysaccharides. After isolation from the plant, gums and starches are converted to powders with low (10% to 12%) moisture content, so they dont require preservatives if stored under proper conditions.
Naturally occurring water-soluble gums exhibit a wide variety of functions: thickening, film-forming, water-binding and/or gelling properties, given specific conditions. Gums can also help mimic fat, due to their gelling and texturizing properties. The properties of these complex carbohydrates are affected by many factors: functional groups as constituents; molecular size; orientation and molecular association; water-binding and swelling; concentration; particle size; and degree of dispersion. (See Table 1 for details on some hydrocolloids derived from natural plant sources, including their chemical nature and functional properties.) Natural hydrocolloid gums can serve as good sources of soluble dietary fiber (about 85% on a dry basis). The soluble fiber has been reported to lower serum cholesterol and improve gastrointestinal function and glucose tolerance.
Gums are also virtually free of fat or oil, contain very little protein and have low moisture content. They consist primarily of complex carbohydrates derived from plants or from the biosynthesis of end products by microorganisms (e.g., xanthan gum). Seaweed extracts also contain an appreciable level of ash, which may naturally occur with the gum or may result from processing.
Natural gum stabilizers include hydrocolloids that come from natural sources and are processed by natural means, such as mechanical or heat extraction, water extraction and not by chemically reactive processes, says Janelle Wilt, Gum Technology Corporation, Tucson, AZ. Such natural hydrocolloids include agar, sodium alginate, carrageenans, guar, konjac, tragacanth, locust bean gum, psyllium, tara gum, fenugreek gum and xanthan gum.
Conventional wisdom says hydrocolloids that are merely extracted from natural sources, like plants, and purified should be considered natural. But because the FDA gives little guidance, the interpretation of the definition is up to the end user. For example, xanthan gum is produced by the fermentative action of a bacteria, Xanthamonas campestris, and is considered by many to be natural in this form, observes Joe Klemaszewski, senior food scientist, Cargill, Minneapolis. Commercial processing of some xanthan gums involves precipitation with isopropyl alcohol. This step is considered by some as a nonnatural processing step even though the hydrocolloid itself has not undergone a chemical change, as is the case of chemically substituted starch.
Starches are generally considered natural ingredients, except when the plant is genetically modified or the starch itself is chemically altered. Processors use wet milling to extract and liberate the starch by grinding aqueous slurries of the raw material. Purification of natural starches is achieved by nonchemical procedures, as specified in the U.S. Food Chemicals Codex. The extracted starch may be pregelatinized by heat treatment in the presence of water to make it cold-water soluble.
Starch is a polymer of glucose (dextrose) and is produced in the plant by a biosynthetic process. Two polysaccharide types occur in most starches: Amylose, a linear polymer, has the tendency to retrograde, and amylopectin, a highly branched polymer, does not easily undergo retrogradation. However, at freezing conditions, amylopectins clarity decreases and its water-holding capacity is reduced.
Food-grade starches come from corn, tapioca, potato, rice, sorghum, wheat and other cereals, and from roots, e.g., potato and tapioca (see Table 2 for more on unmodified starches). Potato and tapioca starches have relatively higher molecular weight than cereal starches and, at low temperature, have less of a tendency to undergo retrogradation (e.g., crystallization, which results from the alignment, association and precipitation of the unbranched amylose chains).
Unmodified starches have a maximum limit of 0.5% protein, except in high-amylose starches, and crude fat must not exceed 0.15%. Moisture content of cereal starches cannot exceed 15%, and tapioca and sago starch cannot exceed 18%.
Much of the starch used in foods today is chemically modified to enhance functionality, says Klemaszewski. The Code of Federal Regulations allows for the addition of specific chemicals to starch for crosslinking, bleaching, acid treatment, and/or substitution.
Some chemicals used in starch modification are naturally occurring, such as hydrochloric acid, enzymes and hydrogen peroxide, while others, such as epichlorohydrin, have stronger chemical connotations. These modifications change the starches properties. This means if a product designer were to work with native starches, which the industry generally considers as natural ingredients, the starch would have less acid stability, heat stability and freeze/thaw stability than its chemically modified counterpart, he continues.
Gums and starches are highly functional ingredients in snack foods, beverages, cereal products and other food systems mainly due to viscosity, water-binding and gelling properties. Viscosity ranges of hydrocolloids can vary significantly (from 10 cps to 4,000 cps at 1% gum level) due to their chemical nature, degree of branching and polymerization.
Hydrocolloid gums, when combined with unmodi- fied starches, can help increase moisture retention, reduce ice crystal growth, act as suspending and adhesive agents, inhibit weeping (syneresis), stabilize foam and emulsions, and improve freeze/thaw stability. Some seaweed extracts, such as agar, carrageenan, pectins and alginates, work as gelling agents in pie fillings, icings and glazes. As a source of fiber, gums such as gum acacia, pectin and guar gum can be used at levels compatible with the end product.
Unmodified starches, with and without pregelatinization, do not have maximum limits of usage. However, the Code of Federal Regulations specifies the maximum use level of gums by various product categories (e.g., bakery, snack foods, salad dressings, confections, etc.). The gum is usually mixed in with the flour in dry mixes. In beverages, sauces and dressings, the gum is allowed to hydrate at the required conditions of temperature, pH, ionic requirements and other cofactors, based on supplier recommendations. The sequence of incorporation, synergy, particle size and chemical nature of the polysaccharide also affect the hydration rate.
When some specific gums are used in combination, it significantly enhances or modifies the functional properties due to synergistic action. For example, a combination of xanthan gum and locust bean gum forms a heat-reversible flexible gel, whereas the individual gums are not gel-forming. The reaction of locust bean gum with kappa carrageenan to yield heat-reversible rigid gels works as a gelling agent in baked goods, desserts and confections. Gums and starches are typically combined in a formulation, since the gums generally help reduce retrogradation problems involved with high-amylose starches.
While all the natural gums share general functionalities in stabilizing foods and beverages, the specifics vary widely. The product designer needs to consider the strengthsand weaknessesof each when choosing the appropriate gum or blend.
Agar, derived from red seaweeds, consists of two repeating units of polysaccharides: alpha-D-galactopyranosyl and 3,6-anhydro-alpha-L-galactopyranosyl alternating segments. The gelling component is known as agarose. Traditional agar can bind about 100 times its weight of water and, when boiled to 212°F and cooled, forms a strong gel. It is one of the most-potent gel-forming gums known and is unique among gums in that the gelation temperature is far below the gel-melting temperature. A solution of agar (1.5%) congeals in the range of 32° to 39°C (89.6° to 102.2°F) but does not melt below 85°C (185°F). This temperature difference between gelation and liquefaction is important for many food applications. For example, the high melting point of agar is important in icing formulations for bakery products and gelled confections stored and/or transported at high temperatures.
A more-recent type of agar does not require boiling, unlike traditional agar. The seaweed sources (Gelidium, Gelidiella or Gracilaria species) are subjected to a series of manufacturing procedures that yield a natural product that can be hydrated at 170° to 180°F, instead of 212°F. This is a desirable feature, considering the expense of boiler operations. A gum system with nonboiling agar and other hydrocolloids has been developed to replace gelatin as the gelling agent in yogurt and other dairy products.
Carrageenan, a water-soluble gum, is isolated from red seaweeds like Eucheuma, Gigartina and Chondrus, among others. Consisting of sulfated linear polysaccharides of D-galactose and 3,6-anhydro-D-galactose, carrageenans act as anionic polyelectrolytes. Due to the presence of the half-ester sulfate groups, a reaction occurs with charged amino-acid chains of proteins to form stable gels or to act as thickeners. The three common types of carrageenanskappa, iota and lambdadiffer in degree and location of sulfated ester groups and the linkage of the repeating units.
An important property of kappa carrageenan is its ability to form gels in the presence of potassium ions, and also to form rigid gels with locust bean gum. This gel-forming ability is beneficial in preparing piping gels, bakery jellies and similar products. Meat injection with brine mixed with semi-refined, natural carrageenan plus starch can reduce cooking losses in poultry and meat. Lambda carrageenan, a nongelling type, binds or retains moisture, and helps suspend cocoa solids in beverages. Iota carrageenan, which requires calcium ions to form a pliable gel, finds use in many fruit applications.
Alginates contain alginic acid, a high-molecularweight linear polysaccharide, that consists of homo- and heteropolymers with polymannuronic and polyguluronic acid units. The guluronic and mannuronic acid content of the seaweed affects the nature of the gel formed. Sodium alginate, in the presence of calcium ions, yields gels that are not thermally reversible. The method of addition and type of calcium salt added will affect the properties of the final gel. A calcium sequestrant can weaken the gel or delay its gelling time.
Sodium alginates, in combination with xanthan, help increase batter viscosity and increase cake volume. They also act as a cold-water gel base for instant bakery jellies and instant lemon-pie fillings. Freeze/thaw stability of the fillings has been reported to improve in samples treated with alginates. In icings, alginates reduce stickiness and cracking.
Gum acacia, also known as gum arabic, is a heteropolysaccharide consisting of an arabinogalactan complex (about 88.0%), an arabinogalactan-protein complex (10.4%) and a glycoprotein fraction (about 1.2%). It also consists of rhamnose and glucuronic acid, in addition to arabinose and galactose. It has excellent emulsifying properties and is unique among other polysaccharides due to its unusually low viscosity (15 cps at 10% solution). The highly branched, compact structure may account for its low viscosity, which can allow a higher percentage of soluble dietary fiber in beverages. Gum acacia is widely used in the food industry for its emulsifying properties, low viscosity, high fiber content, water-binding capacity, and adhesive and film-forming properties.
Unweighted beverage emulsions (e.g., cola drinks) make use of gum acacia as an emulsifying agent. It is also used as a flavor carrier in spray-dried flavors. Due to its low viscosity, 30% to 40% solutions can be prepared, and flavor oils can be encapsulated to form stable dry powders. Gum acacia is a main component in glazing agents, due to its adhesive properties; it also yields a pliable and stable icing base. As a surfactant and foam stabilizer, it can be used in whipped cream or toppings. Since gum acacia is high in dietary fiber, it can also be used as a texturizer and bulking agent in powdered bakery mixes. It is widely used by the confection industry, as it forms coacervates with gelatin.
Guar gums structural building blocks are the sugars mannose and galactose at a ratio of 2:1. The protein content ranges from 3% to 6%. It swells in cold water and is one of the most highly efficient water-thickening agents in the food industry. It also has a high percentage soluble dietary fiber (80% to 85%). It is a low-cost thickening and stabilizing agent in dressings and sauces. When added to cake mixes, it helps improve moisture retention in the finished product. It is a thickening agent and stabilizer for baked goods. Guar also helps to increase volume in yellow cake, probably by aiding in air entrapment. In combination with other hydrocolloids, guar can increase soluble-dietary-fiber content in bread without negatively impacting grain, mouthfeel, crumb body and taste aroma.
Locust bean gum, a natural polysaccharide, is isolated from the pods of a tree, Ceratonia species, of the legume family. It consists of mannose and galactose sugar units at a ratio of 4:1. Unlike guar, which hydrates rapidly in cold water, locust bean gum has to be heated to 80°C (176°F) for full hydration. Food-grade locust bean gum should have a protein content not exceeding 8%, as specified in the Code of Federal Regulations. FDA classi- fies locust bean gum as a direct food additive.
Solutions of locust bean gum are non-Newtonian and have zero yield value; thus, they flow as soon as slight shear is applied. When combined with xanthan, locust bean gum yields pliable gels. It also acts synergistically with kappa carrageenan to form strong, rigid gels. It is shown to have water-binding properties when used in bread doughs. When used at 0.1% to 0.2% in fruitpie fillings, it prevents the water from boiling out. In gel desserts, locust bean gum retards syneresis, or weeping.
Pectins occur in nature mainly in citrus fruits and apple and can form gels at varying suitable conditions. The main component of pectin is D-galacturonic acid partly esterified with methoxyl groups. Pectins can be classified into high methoxy (HM), low methoxy (LM) and amidated pectins. HM pectins require more than 60% solids and low pH to gel, while LM pectins require calcium and may gel at 25% to 35% solids given the proper gelling conditions. Amidated pectins are usually not considered natural. Heat-reversible bakery jellies may be prepared with HM pectins at 55% to 65% solids. Pectins, in combination with other gums, also inhibit syneresis of pie fillings and glazes. In protein beverages, combining pectin with thickeners like guar gum and xanthan gum can help provide suspension and stability.
Xanthan gum, a highly branched polysaccharide, is a biosynthetic product of a bacteria, Xanthomonas campestris. Hence, it is considered natural by the food industry, and has been allowed for food use by many countries, including the United States and Canada. It consists of repeating units of D-glucose, D-mannose and D-glucuronic acid. Food-grade xanthan is an acid-resistant thickener and stabilizer and has an ash content that does not exceed 9.0%. Xanthan gum solutions are extremely pseudoplastic and exceed most common gums in this aspect. Viscosity is reduced with increasing shear; viscosity is regained after shear is released. This property is an advantage when pumping gum-treated liquids.
Xanthan gum is an excellent emulsion stabilizer in salad dressings and sauces. In bakery fillings, the gum prevents water migration from the filling to the pastry due to its water-binding property. It appears to inhibit starch retrogradation and improves shelf life of the finished product.
A natural outlook
According to Greg Andon, president of TIC Gums, Inc., Belcamp, MD, the company offers a variety of certified organic products which qualify for natural labeling. These include guar gum, inulin, locust bean gum and gum acacia. Other natural gums used as stabilizers include carrageenans, agar, pectins, tara gum and konjac. The organic gums may also be offered in combination with other nonorganic gums based on the customer applications that may satisfy a 95% organic claim. Prototype formulations for various food categories, including salad dressings, bakery products, beverages, etc., are available upon request.
The increased demand for organic products has most likely added to the fervor over healthy, natural products since consumers equate organic with being natural as well, says Wilt. Since customers can find almost any product on the shelf which is made of natural ingredients, from cookies, cakes, beverages, baby foods, soup, gravies, dressings and more, they would expect that stabilizers used in the industry would be equally available in any application.
Florian M. Ward earned her Ph.D. in food science from the University of Washington, Seattle, as well as an M.S. in pharmaceutical chemistry, a B.S. in processing technology and a B.S. Pharmacy from the University of the Philippines. Her company, FMWard Consulting LLC, Chadds Ford, PA, offers technical assistance on the use of hydrocolloid systems. She can be reached at [email protected].
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