The July 9 issue of Chemical & Engineering News (alas, behind a paywall -- but worth checking to see if your library has an institutional subscription) has an interesting piece  on the recently-settled trial in which the makers of Equal (an artificial sweetener based on aspartame) sued the makers of Splenda (an artificial sweetener based on sucralose) over their claim in advertisements, "Splenda is made from sugar, so it tastes like sugar." The makers of Equal (a company called Merisant) asserted that this claim was deceptive.
Most of the C&E News piece focuses on the ways the two sides deployed their scientific experts in the courtroom to explain the dispute (and build the case for their way of seeing things, naturally) to a jury of non-scientists.
The sucralose molecule differs from sucrose (table sugar) by three chlorine atoms. One of the central questions in the trial was whether this structural similarity to sucrose is what makes sucralose taste sweet. To examine this question, the jurors couldn't just ponder structural similarities between the two molecules in isolation, but were asked to consider similarities in the ways the two molecules bind to the sweet taste receptors on the tongue.
McNeil Nutritionals (the company that makes Splenda) hoped to persuade the jury with the testimony of Steven Munger, associate professor at the University of Maryland School of Medicine. From the article:
Munger explained that sucralose attaches to two subunits of the sweet receptor, T1R2 and T1R3, in the same way that sugar does. Furthermore, he said, when bound to the receptor, sucralose brings about the same kind of cellular changes as sucrose. The only difference is that sucralose binds far more tightly than sucrose, making it 600 times sweeter, he said.
Munger backed up his argument with data from experiments he had performed. One study employed fluorescence spectroscopy to measure the binding affinity of sucrose and sucralose for T1R2 and T1R3, while another used a synchrotron to measure the conformational change the receptor undergoes when sucrose or sucralose binds to it.
The gist of the argument seems to be that if a molecule that's structurally similar to sucrose binds to the sweet taste receptor in a way that's similar to how sucrose binds to that taste receptor, the similarity in binding ("tastes like sugar") can be attributed to the similarity in structure ("made from sugar").
Of course, Merisant's scientific expert, Eric Walters, a medicinal chemist from Rosalind Franklin University of Medicine & Science, didn't see it that way:
He had three key talking points: First, sucralose's sugarlike taste is not due to any origins from sugar; second, sucralose has off-tastes that sucrose doesn't have, suggesting it binds to taste receptors beyond the sweet taste receptor; and finally, contrary to Munger's findings, sucralose does not bind to the sweet taste receptor in the same place or in the same way as sucrose does.
Walters illustrated his points with data from human taste tests; with an analysis of the three-dimensional structures of sucrose and sucralose; and with a comparison of the stereochemistry of galactosucrose, which is not sweet, with that of sucralose.
This first point is actually the one that makes me question Splenda's slogan. While it isn't made clear in the article, I find myself a little dubious of the claim that sucralose is actually made from sucrose. Is sucrose actually the cheapest staring material to use to synthesize this artificial sweetener? Maybe it is, but given the price of sugar at the store, it would surprise me if there weren't some cheaper material to start with. Also, it's pretty clear to me that starting with sucrose is no guarantee of ending up with something sweet. Burn some sugar -- really burn it -- and taste what you're left with. It isn't sweet.
So, were I a juror, I'd certainly be asking:
- Is it actually made from sugar?
- Does being made from sugar necessarily imply that the product of the synthesis will taste like sugar?
If the answer to either of these questions is "no" then the slogan-writers overreached. And, no matter what the answer to the first question, I know that there is no "conservation of sweetness" in chemical reactions, so the answer to the second question has to be "no".
That seems to be the direction the jury was leaning when the case was settled (though the article speculates that the jurors might have been swayed as much by the relative age and experience of the dueling expert witnesses; the article doesn't speculate as to whether a jury might also have been predisposed to favor the testimony of a chemist over that of a biologist).
Deceptive advertising! Who'd've thunk it?