What Are The Uses And Properties Of Aspartame?
The E number of aspartame in France and Europe is E 951. It was first marketed by NutraSweet AG and more recently by Ajinomoto and Holland Sweetener Company. This sweetener is incorporated into a number of foodstuffs (drinks, desserts, sweets, etc.) and in table sweeteners, under the name Canderel, Pouss-suc and into some 600 medicines; this report does not consider the possible intake (very limited compared with dietary intake) of aspartame from this later source. Its sweetening power is 180 to 200 times greater than that of saccharose.
Aspartame is a dipeptide methyl ester of L-aspartyl-L-phenylalanine. It is a white, odourless, crystalline powder. Its molecular weight is 294.3 Daltons and its rotatory power [a]D22 = 2.3° in 1M HCl.
Its main impurity (approximately 2%) is diketopiperazine, a degradation product of aspartame which has no sweetening properties.
The solubility of aspartame in water is dependent on pH and temperature, the maximum solubility is reached at pH 2.2 (20 mg/ml at 25°C) and the minimum solubility at pH 5.2 (pHi) is 13.5 mg/ml at 25°C.
The stability of aspartame is dependent on time, temperature, pH and water activity (Dziezak, 1986; Bell et al., 1991; Tsoubeli et al., 1991; Homler, 1984; Graves et al., 1987; Huang et al., 1987; Neiderauer, 1998).
Aspartame is very stable in the dry state: at 105°C a loss of approximately 5% (formation of diketopiperazine) is observed after 100 hours of treatment. At 120°C, a 50% loss is obtained after 80 hours of treatment.
In solution, when stored at temperatures ranging from 30 to 80°C, aspartame is progressively degraded into diketopiperazine (Pattanaargson et al., 2000). It is therefore not usable in foods heated at higher temperature (cooking, sterilisation, etc.). At room temperature its stability is good at pH values of between 3.4 and 5 and it is maximum at pH 4.3. At pH below 3.4 the dipeptide is hydrolysed and at a pH greater than 5, cyclisation occurs with the formation of diketopiperazine. In both cases, this transformation results in the loss of sweetness.
In foods with a low or moderate water content (water activities between 0.34 and 0.66), the maximum stability is observed at pH 5.0.
Aspartame has good stability in deep frozen products.