Aspartame is 200
times as sweeter as sucrose. It is commonly used as sweetener in dry products
like sachet dry suspension and chewable tablet. Aspartame is combination of 2
amino acids; Phenylalanine, that is essential amino acid, and aspartic acid,
that is non-essential amino acid.
It has three
major sites for reaction:
- ü
Ester
linkage that undergoes trans-esterification reaction,
- ü
Primary
and secondary anime that undergo Maillard reaction, and
- ü Dipeptide that undergoes reaction with magnesium.
Aspartame is
used as sweetener in dry products. Some formulations of syrup contain aspartame
in some industries due to lack of preformulation studies. Aspartame is
hydrolyzed in presence of water in syrup and is converted to l-aspartyl-l-phenylalanine.
It is derivative of amino acid phenylalanine and has physiological properties
same as phenylalanine. It is toxic to the patient with genetic disease of
phenylketonuria. Phenylketonuria is the genetic disease in which person has
small head, tilted eyes, and behavioral and intellectual problem. Such patients
are unable to metabolize phenylalanine. Aspartame, when incorporated in syrup,
can exacerbate the condition of such patients. This incidence of this disease
is 1 in 12000 people hence its patients in Pakistan are 18000 that cannot use
product with aspartame. Not only in syrup, but it is also converted to
phenylalanine in intestine in any dosage form. Phenylalanine still retains
sweetness but if pH is above 5, it is converted to diketopiperazine derivative
and loses its sweetness.
Aspartame when
used as sweetener along with flavors, it undergoes Maillard reaction which
results in a combined molecule of flavor and aspartame having stronger binding
property with taste buds and giving enhanced flavor property. But it undergoes
such reaction only with the flavors having aldehyde group, this reaction does
not exist with other classes of flavors.
It also has Maillard reaction with lactose which has no effect on product efficacy, but it results in browning of tablet during shelf life after few months. But if aspartame is used as sweetener in chewable tablet containing iron then browning property of this reaction will also be covered.
Aspartame also undergo trans-esterification reaction with sorbitol in syrup and with mannitol in tablet. In this reaction, sorbitol may lose its sweetening and thickening property, but aspartame will retain its sweetness due to availability of active sites.
Aspartame is
also unstable with magnesium stearate. Magnesium attacks on dipeptide bonds and
the resulting product will lose its sweetness. So chewable tablets containing
aspartame should be directly mixed or slugged to prevent it from moisture that
will promote these 3 reactions and use of magnesium stearate as lubricant
should be avoided, it should be replaced with other lubricants i.e., talcum, Aerosil
(Fumed Silica). Magnesium present in talcum is not free for this reaction and
is involved in its internal strong bondings.
Written by: Mudasir Abbas
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