Aspartame is an artificial sweetener used in reduced calorie foods. It is derived primarily from two naturally occurring amino acids chemically combined and designated by the chemical name N-L-aaspartyl-L-phenylalanine-l-methyl ester (APM). Discovered inadvertently in 1965, it was later patented and is currently the most utilized artificial sweetener in the United States.
Aspartame is a white, odorless, crystalline powder. It is about 200 times sweeter than sugar and is readily dissolvable in water. It has a sweet taste without the bitter chemical or metallic aftertaste reported in other artificial sweeteners. These properties make it a good ingredient to use as a sugar replacement in many food recipes. However, aspartame does tend to interact with other food flavors, so it cannot perfectly replace sugar. Recipes for baked goods, candies, and other products must be modified if aspartame is utilized. Although aspartame can be used in microwave recipes, it is sensitive to extensive heating, which makes it unsuitable for baking.
The fact that aspartame provides sweetness and flavor without imparting other physical characteristics such as bulk or calories like other sweeteners makes it unique. Another useful trait is that it has a synergistic effect with other sweeteners, making it possible to use less total sweetener. In addition to sweetening foods, aspartame is used to reduce calories, and intensify and extend fruit flavors.
Humans have desired foods with a sweet taste for thousands of years. Ancient cave paintings at Arana in Spain show a neolithic man taking honey from a wild bee's nest. It has been suggested that early humans might have used the sweet taste of foods to tell them which ones would be safe to eat. It is even thought that the desire for sweet taste might be an innate human trait. Unfortunately, many of the foods that are naturally sweet contain relatively large amounts of calories and carbohydrates.
Alternative sweeteners were developed to provide the sweet taste without the unnecessary calories. They also provide the additional benefits of enhancing the palatability of pharmaceuticals, aiding in the management of diabetes, and providing a cost-effective source where sugar is not available. The first one, saccharin, was discovered in 1879 and has been used in products such as toothpaste, mouthwash, and sugarless gum.
The sugarlike taste of aspartame was discovered accidentally by James Schlatter, an American drug researcher at G.D. Searle and Co. in 1965. While working on an antiulcer drug, he inadvertently spilled some APM on his hand. Figuring that the material was not toxic, he went about his work without washing it off. He discovered APM's sweet taste when he licked his finger to pick up a piece of weighing paper. This initial breakthrough then led the company to screen hundreds of modified versions of APM. However, none of these materials offered all of the advantages found in the original compound, including economical manufacturing, excellent taste quality and potency, natural metabolic pathways for digestion, excellent stability, and very low toxicity. Consequently, the company pursued and was granted United States patent 3,492,131 and various international patents, and the initial discovery was commercialized. The U.S. patent expired in 1992, and the technology is now available to any company who wants to use it.
After many years of toxicity testing, the FDA initially approved aspartame's use as a sweetener in 1980. However, a hallmark of synthetic chemicals used in food products is that their safety is under constant scrutiny. Aspartame is no exception and has been surrounded by some controversy concerning its safety since its introduction. Most of these concerns were put to rest in late 1984, when after investigating various aspartame-related complaints, the FDA and the Centers for Disease Control concluded that the substance is safe and does not represent a widespread health risk. This conclusion was further supported by the American Medical Association in 1985, and aspartame has been gaining market share ever since. In addition to its use in the United States, aspartame has also been approved for use in over 93 foreign countries.
Aspartame has been marketed since 1983 by Searle under the brand names NutraSweet' and Equal'. Currently, NutraSweet' is a very popular ingredient and is used in more than 4,000 products, including chewing gum, yogurt, diet soft drinks, fruit-juices, puddings, cereals, and powdered beverage mixes. In the U.S. alone, NutraSweet®'s sales topped $705 million in 1993, according to the company.
Aspartame is primarily derived from compounds called amino acids. These are chemicals which are used by plants and animals to create proteins that are essential for life. Of the 20 naturally occurring amino acids, two of them, aspartic acid and phenylalanine, are used in the manufacture of aspartame.
All amino acids molecules have some common characteristics. They are composed of an amino group, a carboxyl group, and a side chain. The chemical nature of the side chain is what differentiates the various amino acids. Another characteristic of amino acids is the ability to form different molecular configurations known as isomers. These isomers are designated by the letters L and D. Aspartame is composed of only L, L isomers; none of the other isomer combinations taste sweet. The sweet taste of aspartame could not have been predicted by looking at the two amino acids that it is derived from. L-aspartic acid has a flat taste and L-phenylalanine tastes bitter. However, when the two compounds are chemically combined and the L-phenylalanine is slightly modified, a sweet taste is achieved.
Aspartic acid is one of five amino acids that have a "charged" side group. The charged side group on aspartic acid is (-CH 2 -COOH). When put in water, this material ionizes and becomes negatively charged. Phenylalanine has a nonpolar, hydrophobic side group which is not compatible with water. It is made up of a six carbon ring and is attached to the main amino acid backbone via a methyl (-CH 2 ) group. Prior to synthesis into aspartame, it is reacted with methanol. This adds a methyl group which is linked to the molecule by an oxygen, and the compound is converted to a methyl ester. The methanol required for the synthesis of aspartame has the chemical structure (CH 3 -OH). This is a very common material and is used extensively by organic chemists for various chemical syntheses.
Although its components—aspartic acid, phenylalanine, and methanol—occur naturally in foods, aspartame itself does not and must be manufactured. NutraSweet' (aspartame) is made through fermentation and synthesis processes.
Direct fermentation produces the starting amino acids needed for the manufacture of aspartame. In this process, specific types of bacteria which have the ability to produce certain amino acids are raised in large quantities. Over the course of about three days, the amino acids are harvested and the bacteria are destroyed.
Aspartame can be made by various synthetic chemical pathways. In general, phenylalanine is modified by a reaction with methanol and then combined with a slightly modified aspartic acid which eventually forms aspartame.
The quality of the compounds is checked regularly during the manufacturing process. Of particular importance are frequent checks of the bacterial culture during fermentation. Also, various physical and chemical properties of the finished product are checked, such as pH level, melting point, and moisture content.
Currently, there are only three alternative sweeteners in the United States that can be used in food products. While aspartame is perhaps one of the best available, scientists are looking for new ways to make these sweeteners taste as much like sugar as possible. Their research has been focused in three areas, including finding new derivatives, blending sweeteners, and enhancing the efficiency of aspartame.
Most of the chemical derivative work has centered on finding compounds which will fit into the taste bud receptors better than traditional aspartame. Using aspartame as the model, researchers believe they will be able to improve various characteristics by making slight modifications. For example, they have found that when L-aspartic acid alone is modified in a certain way, it gives products that have a sweet taste. Future research
Another area of research focuses on improving the heat stability of aspartame. Using encapsulation technology, aspartame has been developed which can be used in baked goods and baking mixes. Initial test results are positive, and FDA approval has been granted for bakery applications.
Since only three synthetic sugar substitutes are currently approved for use in food in the U.S., combining artificial sweeteners in products is becoming an important technological advance. Here, scientists combine two or three sweeteners in an effort to make the product taste more sugarlike.
Nabors, Lyn, and Robert Gelardi. Alternative Sweeteners. Marcel Dekker, Inc., 1986.
Best, Daniel and Lisa Nelson. "Low-calorie foods and sweeteners." Prepared Foods, June 1993, p. 47.
Tomasula, Dean. "Sweet as sugar: artificial sweetener producers are blending products, in search of a market winning combination." Chemical Marketing Reporter, June 27, 1994, p. S22.
— Perry Romanowski