aspartame

aspartame

[uh-spahr-teym, a-spahr-, as-per-teym]
aspartame: see sweetener, artificial.

Aspartame (or APM) (or /əˈspɑrteɪm/) is the name for an artificial, non-saccharide sweetener, aspartyl-phenylalanine-1-methyl ester; i.e., a methyl ester of the dipeptide of the amino acids aspartic acid and phenylalanine.

This sweetener is marketed under a number of trademark names, including Tropicana Slim, Equal, NutraSweet, and Canderel, and is an ingredient of approximately 6,000 consumer foods and beverages sold worldwide. It is commonly used in diet soft drinks, and is provided as a table condiment in some countries. It is also used in some brands of chewable vitamin supplements and common in many sugar-free chewing gums and has now been found in some chewing gums that are not sugar free. However, aspartame is not always suitable for baking because it often breaks down when heated and loses much of its sweetness. In the European Union, it is also known under the E number (additive code) E951. Aspartame is also one of the sugar substitutes used by people with diabetes.

Because sucralose, unlike aspartame, retains its sweetness after being heated, it has become more popular as an ingredient. This, along with differences in marketing and changing consumer preferences, has caused aspartame to lose market share to sucralose.

Chemistry

Aspartame is the methyl ester of the dipeptide of the natural amino acids L-aspartic acid and L-phenylalanine. Under strongly acidic or alkaline conditions, aspartame may generate methanol by hydrolysis. Under more severe conditions, the peptide bonds are also hydrolyzed, resulting in the free amino acids.

Properties and use

Aspartame is an artificial sweetener. It is 180 times as sweet as sugar in typical concentrations, without the high energy value of sugar. While aspartame, like other peptides, has a caloric value of 4 kilocalories (17 kilojoules) per gram, the quantity of aspartame needed to produce a sweet taste is so small that its caloric contribution is negligible, which makes it a popular sweetener for those trying to avoid calories from sugar. The taste of aspartame is not identical to that of sugar: the sweetness of aspartame has a slower onset and longer duration than that of sugar. Blends of aspartame with acesulfame potassium—usually listed in ingredients as acesulfame K—are alleged to taste more like sugar, and to be sweeter than either substitute used alone.

Like many other peptides, aspartame may hydrolyze (break down) into its constituent amino acids under conditions of elevated temperature or high pH. This makes aspartame undesirable as a baking sweetener, and prone to degradation in products hosting a high-pH, as required for a long shelf life. The stability of aspartame under heating can be improved to some extent by encasing it in fats or in maltodextrin. The stability when dissolved in water depends markedly on pH. At room temperature, it is most stable at pH 4.3, where its half-life is nearly 300 days. At pH 7, however, its half-life is only a few days. Most soft-drinks have a pH between 3 and 5, where aspartame is reasonably stable. In products that may require a longer shelf life, such as syrups for fountain beverages, aspartame is sometimes blended with a more stable sweetener, such as saccharin.

In products such as powdered beverages, the amine in aspartame can undergo a Maillard reaction with the aldehyde groups present in certain aroma compounds. The ensuing loss of both flavor and sweetness can be prevented by protecting the aldehyde as an acetal.

Public opinion is that aspartame creates an odd aftertaste to some people, many describe it as a non-flavor or something such as a watery aftertaste.

Discovery and approval

Aspartame was discovered in 1965 by James M. Schlatter, a chemist working for G.D. Searle & Company. Schlatter had synthesized aspartame in the course of producing an anti-ulcer drug candidate. He discovered its sweet taste serendipitously when he licked his finger, which had accidentally become contaminated with aspartame.

Following initial safety testing, there was debate as to whether these tests had indicated that aspartame may cause cancer in rats; as a result, the U.S. Food and Drug Administration (FDA) did not approve its use as a food additive in the United States for many years. In 1980, the FDA convened a Public Board of Inquiry (PBOI) consisting of independent advisors charged with examining the purported relationship between aspartame and brain cancer. The PBOI concluded that aspartame does not cause brain damage, but it recommended against approving aspartame at that time, citing unanswered questions about cancer in laboratory rats. Two U.S. FDA Task Force teams investigated the pre-approval research conducted by the manufacturer and found missing raw data, errors, discrepancies in available data, and "a pattern of conduct which compromises the scientific integrity of the studies." The PBOI chose to ignore the FDA Task Force reports. At that point in time, there was no requirement in place in FDA regulations to include brain research in the approval process, only cancer research. Searle's Chief Operating Officer, Donald Rumsfeld, reapplied for FDA certification immediately after U.S. President Ronald Reagan took office. In 1981, Reagan appointed Arthur Hull Hayes as FDA commissioner. Citing data from a Japanese study that had not been available to the members of the PBOI, Hayes approved aspartame for use in dry goods. In 1983, the FDA further approved aspartame for use in carbonated beverages, and for use in other beverages, baked goods, and confections in 1993. In 1996, the FDA removed all restrictions from aspartame allowing it to be used in all foods.

In 1985, Monsanto bought G.D. Searle—and the aspartame business became a separate Monsanto subsidiary, the NutraSweet Company. On May 25 2000 Monsanto sold it to J.W. Childs Equity Partners II L.P. The U.S. patent on aspartame expired in 1992. Since then the company has faced hot competition in market for aspartame from other manufacturers, including Ajinomoto, Merisant and the Holland Sweetener Company, which stopped making the chemical in late 2006 because "global aspartame markets are facing structural oversupply, which has caused worldwide strong price erosion over the last 5 years" making the business "persistently unprofitable”.

Several European Union countries approved aspartame in the 1980s, with EU-wide approval in 1994. The European Commission Scientific Committee on Food reviewed subsequent safety studies and reaffirmed the approval in 2002. The European Food Safety Authority reported in 2006 that the previously established Adequate Daily Intake was appropriate, after reviewing yet another set of studies.

Metabolism

Upon ingestion, aspartame breaks down into several residual chemicals, including aspartic acid, phenylalanine, methanol, and further breakdown products including formaldehyde, formic acid, and a diketopiperazine. There is controversy surrounding the rate of breakdown into these various products and the effects that they have on those that consume aspartame-sweetened foods.

The naturally-occurring essential amino acid phenylalanine is a health hazard to those born with phenylketonuria (PKU), a rare inherited disease that prevents phenylalanine from being properly metabolized. Since individuals with PKU must consider aspartame as an additional source of phenylalanine, foods containing aspartame sold in the United States must state "Phenylketonurics: Contains Phenylalanine" on their product labels.

In the UK, foods that contain aspartame must list the chemical among the product's ingredients and carry the warning "Contains a source of phenylalanine" – this is usually at the foot of the list of ingredients. Manufacturers should print '"with sweetener(s)" on the label close to the main product name' on foods that contain "sweeteners such as aspartame" or "with sugar and sweetener(s)" on "foods that contain both sugar and sweetener". "This labelling is a legal requirement", says the country's Food Standards Agency.

Controversy

Health concerns

Aspartame has been the subject of controversy regarding its safety and the circumstances of its approval by the American FDA and European FSA. Aspartic acid, into which aspartame is metabolized, is a known NMDA receptor agonist. Aspartame itself has been shown to have antinociceptive properties through affecting NMDA receptors in mice. Some studies have also recommended further investigation into possible connections between aspartame and negative effects such as headaches, brain tumors, brain lesions, and lymphoma. These findings, combined with possible conflicts of interest involving HHS employees in the approval process, have engendered vocal activism regarding the possible risks of aspartame.

References

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