All About Sweeteners: Aspartame

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All About Sweeteners
by D. Eric Walters, Ph.D.

Artice of the week:

Aspartame

Other names:
NutraSweet®
Equal®
Canderel®
L-aspartyl-L-phenylalanine methyl ester
N-L-alpha-Aspartyl-L-phenylalanine 1-methyl ester
3-Amino-N-(alpha-carboxyphenethyl)succinamic acid N-methyl ester
APM
SC-18862
E 951 (European registry number)

Taste:

Aspartame has a sweet taste with minimal bitterness for most people. Its onset of sweetness may be slightly slower than sucrose, and the sweetness may linger. The sweetness potency relative to sucrose is about 180, but depends upon the concentration of sucrose which is being matched. The concentration vs. response relationship in water is shown below (results in food systems will vary). This graph is based on data from DuBois, Walters, Schiffman, Warwick, Booth, Pecore, Gibes, Carr & Brands in "Sweeteners: Discovery, Molecular Design, and Chemoreception," D.E. Walters et al., Eds., American Chemical Society, 1991. The equation allows you to calculate sweetness response (R) for any concentration (C). The units of R are percent sucrose equivalent; the units of C are parts per million (ppm).

Aspartame sweetness concentration-response curve

Calories:
Aspartame is composed of two amino acids which are building blocks of proteins; like proteins, it provides about 4 calories per gram. The high potency, relative to sucrose, means that you don't need to use very much, so the the calorie contribution in food systems is typically 0-2 calories.

Safety:
Aspartame is digested in the body. The safety of aspartame has recently been extensively reviewed by the FDA, the Scientific Committee on Food of the European Commission, and several other regulatory agencies around the world. On the basis of hundreds of scientific studies, these agencies all conclude that aspartame is safe. The exception is for people with the rare genetic disorder phenylketonuria (PKU); these people must carefully monitor their consumption of the essential amino acid phenylalanine, which is a component of aspartame.
I have written an essay on the metabolism of aspartame.

Chemistry:

Molecular formula: C14H18N2O5

Molecular weight: 294.31

Aspartame chemical structure

Properties:
The stability of aspartame in the dry state is very good. In food systems its stability is pH-dependent. It is most stable at pH 4.3, in the pH range of many soft drinks. Its stability is also temperature-dependent, breaking down faster at higher temperatures. This limits aspartame's use in baked goods.

Discovery:

It was December, 1965. Jim Schlatter, a chemist at G.D. Searle, was working on a project to discover new treatments for gastric ulcers. To test new anti-ulcer drugs, the biologists used a tetrapeptide (four amino acids) normally produced in the stomach; Schlatter was synthesizing this tetrapeptide in the lab, and one of the steps in the process was to make a dipeptide intermediate, aspartyl-phenylalanine methyl ester.

In the course of his work, Schlatter accidentally got a small amount of the compound on his hands without noticing it. Later that morning, he licked his finger as he reached for a piece of paper, and noticed a sweet taste. His curiosity drove him to ask "Where did that sweet taste come from?" His first thought was of the doughnut he had eaten during his coffee break, but he realized that he had been to the bathroom and had washed his hands since then. It could only be the aspartyl-phenylalanine methyl ester he had worked with. He knew that aspartic acid and phenylalanine, which make up this product, are natural amino acids present in all proteins, so he felt it would be safe to taste the material. It was sweet! He and his lab partner, Harman Lowrie, both tasted the material in 10 milliliters of black coffee, noting the sweet taste as well as the absence of any bitter aftertaste, and recorded the results in Schlatter's laboratory notebook. His boss, Bob Mazur, convinced the company of the potential value of this discovery. Twenty years later, Schlatter's curiosity had produced a billion dollar per year sweetener.