Diet Pepsi's how sweet it is?

Aspartame, which is more commonly known as Equal, is 200 times sweeter than table sugar, or sucrose. And sucralose — the stuff found in Splenda packets that will now be used to sweeten Diet Pepsi — is even sweeter than that. On average, sucralose is 600 times sweeter than table sugar, according to the Calorie Control Council, a non-profit organization that disseminates information about low-calorie foods and beverages.

But peoples' ability to distinguish between the two artificial sweeteners doesn't necessarily have anything to do with sucralose's extreme sweetness, said Stuart McCaughey, an assistant professor of neuroscience at Ball State University in Indiana, who studies taste perception. People can tell the difference between artificial sweeteners because they are sensitive to the "nonsweet tastes" associated with these substances, McCaughey told Live Science in an email.

"All sweeteners also have other aspects of their tastes, which affect how much people like them, and these other sensitivities might differ between people for a variety of reasons," said McCaughey, who added that bitterness is one of the tastes that might turn people off from artificial sweeteners.

People have different gene sequences that affect the way they perceive bitter tastes, according to McCaughey. There are also lots of different taste receptors (cells inside of taste buds) for bitterness in the mouth, and these taste receptors differ in every individual. So, it makes sense that one person might perceive the taste of a certain artificial sweetener as bitter while someone else does not, he said. It also makes sense that some Diet Pepsi drinkers might like the soda sweetened with aspartame, but not with sucralose, and vice versa.

There are also other preferences not related to taste receptors that affect whether or not a person will like a particular sweetener, McCaughey said. One of these is "mouth-feel," or the tactile sensations and textures that a food or beverage imparts in the mouth. Milk, for example, can be described as having a creamy mouth-feel and wine aficionados frequently describe the different mouth-feels imparted by their preferred vintages.

In news reports about Pepsi's new diet drink formula, PepsiCo vice president Seth Kaufman has been reported as saying that the company's new diet soda will have a "slightly different mouth-feel" than its aspartame-sweetened counterpart. It remains to be seen how die-hard Diet Pepsi fans will react to the new formula's mouth-feel, which could perhaps be slightly less (or slightly more) "syrupy" than Diet Pepsi sweetened with aspartame, according to McCaughey. [The 7 Other Flavors Humans May Taste]