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Aspartame

Aspartame is an artificial sweetener, also known as E951. An artificial sweetener is matter which is not a sugar, but which, just like sugars, stimulates the sense for sweet taste. Nowadays, in many products sugar is replaced by these artificial sweeteners.
Aspartame is one of the intensive sweeteners. This means the sweetening strength of aspartame is 150 to 200 times larger than sugar. Therefore smaller quantities need to be added resulting in less energy supplied by the sweetener. The taste of aspartame is very similar to the taste of sugar. Aspartame also enhances the taste of other sweeteners, fruit and fruit aromas and has no unwanted additional flavour or after-taste.
Chemically, aspartame is a combination of the amino acids, aspartic acid and L-phenylalanine, with a methanol-group at the phenylalanine-part.  This combination is very common in nature, but the matter is artificial due to the methyl ester. Because of the presence of phenylalanine, the warning ‘contains a source of phenylalanine’ must be mentioned on the container.

Aspartame is very stable in sour products, but falls apart during heating, loosing its sweet taste. Therefore aspartame is mainly used for light soft drinks and other foods which are prepared without heating.

Production aspartame

Fermentation

The amino acids L-aspartic acid and L-phenylalanine are formed by direct fermentation by means of the bacteria Brevibacterium flavum and Corynebacterium glutamicum. The fermentation process starts with a pure culture of a bacteria, which multiplies in the presence of the necessary nutrients.
When a sufficient amount of bacteria is formed, it is transported to a tank in which all the nutrients are presents which ensure the formation of even more bacteria. Carbon and nitrogen sources are also presents, as they are needed for the production of large amounts of amino acids in a later stadium of the production process. A mixer is used to keep the whole moving and a pump is used to supply filtered, compressed air.
The bacteria start to produce large amounts of amino acids in a fermentation tank with the same nutrients. The whole is kept at the desired pH by means of ammoniac water. 

Isolation

When the right amount of amino acids are formed, the desired acids must be isolated. A large part of the amino acids is separated from the bacteria by means of a centrifuge. An ion exchanger is then used to purify and separate the desired amino acids again. The separated amino acids are pumped to a crystallizing tank, after which the formed crystals are separated by means of a centrifuge. The amino acids are then dried and prepared for the synthesis of aspartame.

Modification

In general, the synthesis of aspartame starts with the modification of aspartic acid and phenylalanine.
The aspartic acid is modified in such a manner that certain parts of the molecule are protected, by for example benzene rings, in order for other chemical reactions to effect only the right parts of the aspartic acid.

L-phenylalanine with a methyl ester is created due to a reaction of phenylalanine with methanol. The chemical equation below shows this reaction.

Synthesis

The modified amino acids are pumped to a reactor, where they are mixed at room temperature for 24 hours. The temperature is then raised to 65°C, after which the whole is kept at this temperature for another 24 hours. After this period of time, the mixture is cooled to room temperature, diluted with a solvent and cooled to -18°C, in order for crystallisation to start. The formed crystals are then isolated by means of filtration and dried.

Modification

In a big tank, a reaction with acetic aid is used to convert the formed crystals into aspartame. The whole of crystals, acetic acid solution, palladium catalyst and hydrogen in this tank, is intensively mixed for 12 hours, in order for the matter in the mixture to have enough time to react with each other.

Purification

After a reaction time of 12 hours, the catalyst is removed by means of filtration and the solvent by means of distillation. The remaining solid residue is dissolved in ethanol and crystallised again. Finally, the aspartame crystals are filtered and dried.

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User comments

2017-11-30 08:14:57

Name: dorine coenen
fijn voor in de klas te gebruiken als achtergrond informatie

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