Diet Pepsi drinkers only have a few more days to enjoy their favorite aspartame-sweetened beverage fresh from the soda fountain. Starting in August, the popular diet soda will get its sugary taste from a different, and less controversial, artificial sugar called sucralose (popularly known as Splenda). However, PepsiCo recently announced that fans of the old diet soda recipe will still be able to buy the aspartame-flavored drink online.

The company's decision to sell two versions of the same drink suggests that some Diet Pepsi fans aren't thrilled about the switch to sucralose. And it makes sense that there are dissenters. Despite the controversy over aspartame's safety as a food ingredient (a debate that goes back decades), many people really like the way the fake sugar tastes.

But will people really be able to tell the difference between a diet soda sweetened with aspartame and one sweetened with sucralose? Experts say yes. [9 Snack Foods: Healthy or Not?]

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]

Vintage taste

While people may have their own preferred artificial sweeteners, it's not likely that Diet Pepsi drinkers who like aspartame best will really buy the old version of the drink online. The people who will really care about Diet Pepsi's change in taste are the "superusers" who drink "a six pack a day, at least" of Diet Pepsi, said Brian Wansink, a food psychologist and director of the Food and Brand Lab at Cornell University in Ithaca, New York, and author of "Slim By Design: Mindless Eating Solutions for Everyday Life" (William Morrow, 2014).

PepsiCo's decision to keep stocking the aspartame-sweetened version of its diet soda online probably has a lot to do with its superusers' devotion to the old recipe, Wansink told Live Science. But this isn't the only group the company is catering to: PepsiCo is almost certainly trying to appease the "truists" as well, he said.

Truists are people who just don't like the products they use to change, Wansink said. They tend to have a vision of the way things should be, and they like when brands stick to that vision, he added.

"It's not just [a] sweetener. It's any ingredient or attribute associated with the brand," Wansink said, "The same thing happens every time there's a new upgrade to a Mac or Windows operating system. Even if it's better, there are a lot of people out there saying, 'Why, oh why?'"

Companies have been keeping old-school products around to appeal to this group of nostalgic naysayers (as well as superusers) for years. For instance, Coca Cola continues to sell Tab Cola decades after it replaced the soda with Diet Coke. And if you look closely, you may find that old-school products most notably, candies line the shelves of a few, select establishments in the United States.

In fact, on your next trip to a Cracker Barrel or the movie theater, keep your eyes peeled for candies you haven't seen since your youth. Necco wafers (those crispy little sugar wafers wrapped in wax paper), Good & Plenty (little pill-shaped licorice blobs), the original Dubble Bubble (that rock-hard pink chewing gum) these vintage treats are still manufactured in limited quantities. The fact that they're still on shelves has a little something to do with the truists and a little something to do with the fact that, in the ever-evolving chemistry lab of processed foods, some people refuse to ditch the old ingredients for the new.

Follow Elizabeth Palermo @techEpalermo. Follow Live Science @livescience, Facebook& Google+. Original article on Live Science.

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