Aspartame: The Amino Acid-Based Sweetener
Aspartame is a popular non-nutritive sweetener composed of two amino acids: L-aspartic acid and L-phenylalanine. These amino acids are esterified to form the dipeptide, which possesses an intense sweetness that is around 200 times greater than sucrose (table sugar). Because of its high potency, only a small amount is needed to sweeten food and drinks, making its caloric contribution negligible.
Unlike many other intense sweeteners, aspartame is metabolized by the body into its constituent amino acids, similar to how proteins from common foods like meat and dairy are broken down. However, it is not heat-stable and loses its sweetness when exposed to high temperatures, which limits its use in baked goods. This characteristic makes it ideal for use in products like diet sodas, chewing gum, and certain desserts that do not undergo high-heat processing.
The Synthesis of Aspartame
The creation of aspartame involves a synthesis process that combines the two specific amino acids. First, L-aspartic acid and L-phenylalanine are produced, often through microbial fermentation. In the past, acid hydrolysis of gluten was used, but modern methods utilize bacteria like Corynebacterium glutamicum to excrete the necessary amino acids. Once isolated, the two amino acids are chemically bonded together in a process that forms a peptide bond, followed by the esterification of the phenylalanine component with a methyl group to create the final aspartame molecule.
Safety and Metabolism
The safety of aspartame has been extensively reviewed by regulatory bodies worldwide, including the U.S. Food and Drug Administration (FDA) and the Joint Expert Committee on Food Additives (JECFA). These reviews have consistently concluded that aspartame is safe for the general population when consumed within approved limits. A key consideration for aspartame consumption is for individuals with the rare genetic disorder phenylketonuria (PKU), who cannot properly metabolize phenylalanine. For this reason, foods containing aspartame must include a label warning for those with PKU.
Once ingested, aspartame is broken down in the gastrointestinal tract into aspartic acid, phenylalanine, and a small amount of methanol, all of which are handled by the body without concern for most people.
Other Sweetening Amino Acids and Sweet Proteins
While aspartame is the most prominent amino acid-derived sweetener, other amino acids and related protein compounds also possess sweet properties or act as flavor enhancers.
Glycine
- Mild Sweetness and Flavor Profile: Glycine is the simplest amino acid and has a naturally sweet taste, which gives it its name from the Greek word for "sweet" (glykys).
- Uses: It is used in food applications not just for its mild sweetness but also for its ability to temper the bitterness, saltiness, and sourness of other ingredients. It can be found in protein shakes and certain food products.
Sweet Proteins
Several tropical plants produce intensely sweet proteins that are composed of amino acid chains, though they are not single amino acids themselves.
- Thaumatin: Extracted from the katemfe fruit (Thaumatococcus daniellii), this protein is up to 3,000 times sweeter than sucrose. It is approved in some regions as both a sweetener and a flavor enhancer.
- Monellin: A sweet protein from the serendipity berry (Dioscoreophyllum cumminsii). While it has not received widespread approval as a general-purpose sweetener in the U.S. due to its sensitivity to heat and pH, it is approved in Japan.
- Brazzein: Another sweet protein from the West African plant Pentadiplandra brazzeana. It is extremely sweet and more heat-stable than monellin.
Amino Acid Comparison Table
| Feature | Aspartame | Glycine | Thaumatin | Monellin |
|---|---|---|---|---|
| Sweetness (vs. Sucrose) | ~200x | Mildly Sweet | 2,000-3,000x | 100-1,000x |
| Source | Synthetic dipeptide from Aspartic Acid and Phenylalanine | Found in all living cells; industrially produced | Tropical Katemfe fruit | Tropical Serendipity berry |
| Heat Stability | Not heat stable; loses sweetness when heated | Stable | Heat stable | Not heat stable |
| Primary Use | Diet sodas, chewing gum, instant foods | Seasoning, flavor enhancement, supplement | Flavor enhancer and sweetener | Flavor modifier, chewing gum |
| Caloric Content | 4 calories per gram; negligible in use amounts | Yes, but used in small quantities | Caloric; used in such small amounts that it's negligible | Caloric; used in such small amounts that it's negligible |
Conclusion: The Amino Acid Sweetener Landscape
In summary, while several amino acids have sweet or flavor-enhancing properties, the most widely recognized and utilized amino acid-based sweetener is aspartame. It is created from two fundamental amino acids, aspartic acid and phenylalanine, and provides a sugar-like sweetness with minimal calories. Other amino acid derivatives and sweet proteins, like glycine and thaumatin, also play distinct roles in the food industry due to their unique flavor profiles and properties. The choice of sweetener depends on the specific application, from diet beverages sweetened with aspartame to the use of glycine for flavor modification in certain savory foods. All these compounds demonstrate the versatility of amino acids beyond their role as protein building blocks, contributing to the flavor complexities of the modern food supply. For more information on aspartame's regulation, visit the FDA website.
