For the product developer involved in the beverage industry, aspartame is still a respected high intensity sweetener, to be used to replace bulk sweeteners to achieve amongst other effects reduced calorie products. I say ‘still’ because the ingredient continues to flit across the media airwaves as reports, mostly conflicting, assess its toxicology and impact on health. My aspartame issues tend to revolve around its degradation over shelf-life  especially in low acid to neutral products. The ingredient is about 120 to 220 times sweeter than sucrose (Homler, 1984).

To understand  aspartame performance more fully, means to appreciate its chemical structure. It is a dipeptide, N-L-or-aspartyl-Lphenylalanine-l-methyl ester, (α-APM) which is regulated by both the FDA and EU legislation (Mortensen, 2006) in terms of the amounts that can be used in foodstuffs. It’s E-number is E 951 and has an ADI of up to 40 mg  per kg body weight per day.  It is used extensively in a variety of dry foods, confectionary, and dairy and fruit beverages as well as a typical tabletop sweetener.  It is perceived to enhance acid fruitiness.

Aspartame is determined by a variety of methods – reaction with N-bromo succinamide (Viplava Prasad et al., 1988) yields a coloured solution measured by spectrophotometry. HPLC and reverse phase HPLC are more commonplace because of the better levels of accuracy with small quantities of analyte and lower levels of interference from competing substances (Prodolliet and Bruelhart, 1993). More advanced methods of use coupled fluorescence and ultraviolet detection  in two-dimensional HPLC (Cheng and Wu, 2011).

Studies on its stability abound and the mechanisms of degradation were largely worked out in the 70’s and 80’s in a variety of food systems-  (Mazur, 1976; Schertz et al., 1983; Homler,1984; Prudel et al., 1986; Bell and Wetzel, 1995). The levels of degradation depends on the pH, buffering capacity and temperature of the food in which it resides. It degrades at temperatures above 150 °C which makes it unsuitable for most baked products.  A recent examination of this phenomenon using isothermal thermogravimetry  and HPLC was made (Conceicao et al., 2005).

Aspartame degradation follows acid-base catalysis in solution with the formation of 3,6-dioxo-5-phenylmethyl-2-piperazineatic acid (DKP) which is the major decomposition product (Furda et al., 1975). All the degradation products are non-sweet so there is a slow loss of this sweetness over shelf-life. The mechanism of decomposition in acid  to neutral pH solutions involves an intramolecular cyclization with the loss of methanol. As well as DKP formation, L-aspartic acid, L-phenylalanine, L-phenylalanine-l-methyl ester (Schertz et. al., 1983; Prudel et al, 1986; Stamp and Labuza,1989) and the structural isomer of aspartame P-APM (Stamp and Labuza, 1989) are all produced.

The main suppliers of aspartame are Ajinomoto through its AminoSweet® brand although a number of sources can be found in China such as Nuitang and Heifei TNJ.

References

Bell, L.N., Wetzel, C.R. (1995) Aspartame degradation in solution as impacted by buffer type and concentration. J Agri Food Chem 43(10)  pp. 2608-2612

Cheng, C., Wu, S.C. (2011) Simultaneous analysis of aspartame and its hydrolysis products of Coca-Cola Zero by on-line postcolumn derivation fluorescence detection and ultraviolet detection coupled two-dimensional high-performance liquid chromatography. J Chromatogr A. 1218  pp. 2976-83.

Conceicao, M.M., Fernandes Jr., V.J., Souza, A.G., Nascimento, T.G., Aragao, C.F.S., and Macedo, R.O. (2005). Study of thermal degradation of aspartame and its products of conversion in sweetener using isothermal thermogravimetry and HPLC. Thermochimica Acta433  pp. 163–169.

Furda, I., Malizia, P.D., Kolor, M.G., Vernieri, P.J. (1975). Decomposition products of L-aspartyl-L-phenylalanine methyl ester and their identification by gas-liquid.chromatography. J. Agr. Food Chem. 23(2) pp. 340.

Homler, B.E. (1984). Properties and stability of aspartame. Food Technol. 38 pp. 50

Mazur, R.H. (1976). Aspartame-A sweet  surprise. J. Toxicol. Environ. Health. 2  pp. 243

Mortensen, A. (2006). Sweeteners permitted in the European Union: safety aspects. Scand. J. Food Nutrition, 50, pp. 104–116.

Prodolliet, J., Bruelhart, M. (1993). Determination of aspartame and its major decomposition products in foods. JAOAC Int., 76, pp.  275–282

Prudel, M., Davidcova, E., Davidek, J., Kminek, M. (1986). Kinetic decomposition of aspartame hydrochloride (USAL) in aqueous solutions. J. Food Sci. 51(6): pp.1393

Schertz, J., Monti, J.C., Jost, R. (1983) Analysis of the peptide sweetener aspartame by liquid chromatography. Lebensm. Untersforsch und Technol . 177  pp.124.

Stamp, J.A., Labuza, T.P. (1989). An ion-pair high performance liquid chromatographic method for the determination of aspartame and its decomposition  products. J. Food Sci. 54(4)  pp. 1043.

Viplava Prasad, U., Divakar, T.E., Sastry, C.S.P., Rao V. & Kapur, O.P. (1988). New methods for determination of aspartame. Food Chem., 28, pp. 269–276