Aspartame A white, crystalline compound, 1-aspartyl-1-phenylalanine methyl ester (APM), with formula as shown in the figure. It is slightly soluble in water. Its sweetening pro­perties were discovered accidentally in 1965 when the compound, a dipeptide, was produced as an intermediate in the synthesis of the C-terminal tetrapeptide of gastrin. Aspartame is the L,L-diastereoisomer; the three other possible diastereoiso­mers are not sweet. The taste of aspartame would not have been predictable based on its component amino acids, aspartic acid and phenylalanine.

The sweetness of aspartame relative to sucrose is a function of the latter’s concen­tration, and is also dependent upon the presence of other flavors and materials. In a number of applications, such as chewing gum and various fruit-flavored products, aspartame favorably extends and enhances the flavor perception, and it shows synergy with other sweeteners. The sweetness perception may also last longer with aspartame than with sucrose or other sweeteners. See SUCROSE.

Aspartame is metabolized to its component amino acids, which are further metab­olized by the usual metabolic pathways. Under certain conditions of heat and pH in aqueous solution, aspartame is transformed into its diketopiperazine derivative, 3,6- dioxo-5-benzyl-2-piperazineacetic acid (2), which is tasteless.

This property limits the use of aspartame when it is exposed to high temperatures, such as in baking. The stability of aspartame in aqueous solution is pH-dependent; it is most stable at a pH of approximately 4. The rate of conversion (its half-life is 262 days at 77°F or 25°C) is sufficiently slow under the conditions of normal use that aspartame has found an increasing number of applications in various food products, and is particularly successful in soft drinks. The safety of aspartame has been established by studies in animals and human beings. Aspartame has been approved in many countries for uses in both dry and wet applications.