Les Jones

Science > So Sweet, So Fake

Wired has an article about the pursuit of the perfect artificial sweetener. Most of the candidates are enantiomers: mirror-images of a substance with an identical chemical formula.

Louis Pasteur discovered enantiomers in his studies of tartaric acid, which produces two different crystals. Pasteur separated the crystals by hand under a microscope, dissolved them in solution, and passed a light through the solution. One set of crystals rotated light to the left (the laevus, or L- enantiomer), while the other rotated light to the right (the dexter, or D- enantiomer). The different forms are said to be chiral versions of one another.

Either enantiomer typically works equally well in chemical reactions, but not necessairly in biological reactions. Biological reactions are mediated by enzymes, and enzymes have evolved so that their folded structures only interact with the common enantiomer found in nature. Luckily for food scientists, the taste buds are generally non-specific, and will detect the chiral form as sweet. Most natural sugars are the D- version, while the artificial sweeteners are the L- version.

One new sweetener is the D- version of tagatose. Tagatose is one of the rare sugars that occurs in nature in the L- form. The human body only metabolizes about 25% of the calories in the D- version of tagatose. The taste buds respond to tagatose because it is similar to L- fructose.

Two interesting points from the article. One, saccharin was discovered a long time ago, in 1879. Two, most of the discoveries of artificial sweeteners happened because a chemist spilled a chemical in his hand and later stuck his finger in his mouth. Now that's good chemistry!