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What's in
a sweetener? patch ita swat 3 ee
The chemicals below are
all artificial sweeteners i.e. sugar substitutes. Some of
them are available as tablets as a sugar substitute and
others appear as ingredients in many food products, not
just in 'diet' foods.
In America alone the
market for sweeteners is worth over $1 billion. The
market leader is aspartame, which was approved for use in
the USA in 1981 and Nutrasweet's patent expired in 1992.
The chemical name for aspartame is N-L-à-aspartyl-L-phenylalanine
1-methyl ester so its easy to see why the name aspartame
has stuck! It is metabolised in the body but because it
is 180 times as sweet as sucrose it is essentially
non-caloric. It is marketed under the brand name
NutraSweet. One of the drawbacks of aspartame is its
instability to heat and acid.
Exercise: Bring in a variety of food labels and
find out how many products contain artificial sweeteners
and which sweeteners are in use.
Acesulfame-K ( potassium salt of
6-methyl-1,2,3-oxathazin-4(3H)-one 2,2 dioxide) is a
sweetener which was approved by the FDA in 1988 for dry
mixes, table uses and chewing gum. It is 200 times as
sweet as sugar and it is not metabolised and in thus
noncaloric.
Food products often contain a mixture of sweeteners. This
is because it has been found that they have a synergistic
effect whereby the sweetness of a mixture is greater than
that of the individual components. This means less can be
used to get the same apparent sweetness.
Sucralose (1,6-dichloro-1,6-dideoxy-á-D-fructofuranosyl-4-chloro-4-deoxy-à-D-galactopyranoside)
which is the only non-nutritive sweetener based on
sucrose. It is selectively chlorinated and the glycosidic
link between the two rings is resistant to hydrolysis by
acid or enzymes, so it is not metabolised. It is 400-800
times the sweetness of sucrose, it is very soluble in
water and it is stable to heat.
It has been developed by Tate and Lyle (who else?) and
McNeil Speciality Products in the USA.
How does one measure sweetness? As far as I know no-one
has yet invented a sweetness meter since it is
essentially a physiological sensation. Sweetness thus has
to be tested by human testers: the sweetness of solutions
of different concentrations are compared to that of
standard sugar solutions until they appear the same. The
ratio of concentrations then gives the sweetness ratio.
Alitame (L-à-aspartyl-N-(2,2,4,4-tetramethyl-3-thietanyl)-D-alaninamide)
is a sweetener based on an amino acid. like aspartame. It
is 2000 times as sweet as sugar and although it is
metabolised,so little is needed that it is noncaloric.
Imagine, 1 g can replace 2 kg of sucrose! Alitame has
been developed by Pfizer and has a 'sweet, clean taste'.
The oldest artificial sweetener is, of course, saccharin
(the calcium or sodium salt of
1,2-benzisothiazol-3(2H)-one 1,1-dioxide) which has been
marketed for over a century. It is 300 times as sweet as
sucrose, but many people don't like its bitter
aftertaste. It is also controversial as some animal
studies showed that massive doses of saccharin produced
cancer. However, it was not banned as the evidence of
harm to humans wasn't there and the levels fed to rats
were so high that almost anything would have produced
cancer. It is widely used in a variety of products and
the health risk, compared to the risk of over-consumption
of sucrose, appear slight.
Another controversial
sweetener is cyclamate (sodium cyclohexylsulphamate),
produced by Abbott Laboratories. This was banned by the
FDA in 1970. It is not banned in the EU. It is only 30
times as sweet as sucrose, which doesn't give it a strong
competitive advantage.
Several possible
sweeteners are under evaluation which are derived from
natural sources: stevioside from a South American plant;
glycyrrhizin from licorice root; thaumatin, a mixture of
proteins from a West African fruit.
The most interesting
potential sweetener from a chemical point-of-view is
left-handed sucrose! Sucrose is optically active, as are
many biologically active molecules, and natural sucrose
is right-handed. The other optical isomer would be sweet
but would not be recognised in the boy and would thus not
be metabolised. However, the synthesis of this alien form
of sucrose (it does not occur naturally) would be very
difficult and it is hard to see it being produced (even
if it were possible) at a cost to compete with other
artificial sweeteners. It is, however, an excellent
example of the importance of optical activity or the
having the correct handedness in biology.
Not all sugars are sucrose
Commonly when we talk of 'sugar' we are thinking of
sucrose, a particular disaccharide produced by sugar cane
and sugar beet. But sucrose is only one member of a
family of sugars: they are related chemically but have
different structures and different sweetnesses. Some
sugars have one sugar molecule - they are monosaccharides
e.g. glucose; others have two sugar units joined, like
sucrose, and are disaccharides. Starch and cellulose
contain many sugar units linked together - they are
polysaccharides. However, starch and cellulose they
aren't sweet and only mono- or disaccharides have small
enough molecules to register as sweet on the tongue. If
you chew a piece of bread and then allow it to stay in
the mouth it starts to taste sweet as the enzyme in
saliva breaks up the starch molecules into simple sugars.
What is invert sugar?
We are more familiar with 'invert sugar' as honey or
golden syrup. Invert sugar is sucrose which has been
hydrolysed to split the disaccharide into its component
sugars: fructose and glucose, the same process that
happens in the mouth and in digestion. It is called
invert sugar because hydrolysis of sucrose causes the
solution to alter the rotation of polarised light, an
effect known as the inversion of sucrose.
Typical artificial
sweetener:
Note the warning "Contains a source of
phenylalanine"
The table below shows the sweetness of several common
sugars relative to sucrose:
| Name |
Sweetness |
| Fructose |
1.73 |
| Invert sugar |
1.30 |
| Sucrose |
1 |
| Glucose |
0.74 |
| Maltose |
0.32 |
| Lactose |
0.16 |
There is an excellent
account of the chemistry of sweeteners in John Emsley's
prize-winning book The Good Chemical Guide Freeman 1995
(ch. 2 "Sweetness and Light").
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