Fans of Diet Pepsi may notice something different: the soft drink beverage is quietly changing its sweetener as part of a major rebranding set for next month.

The change comes as PepsiCo Inc. looks to reinvigorate its namesake brands after losing market share to Coca-Cola co. in recent years. Yet the sweetener change will not be explicitly communicated in the ads, which will feature actress Sofia Vergara.

Cans of Diet Pepsi around the country now list a mix of two artificial sweeteners, a pairing that is commonly found in newer diet sodas. Previously, Diet Pepsi only used aspartame, which is sensitive to heat and breaks down more easily.

This summer, PepsiCo declined to say whether it would go ahead with such a change after reports surfaced that it was testing new sweeteners. Although the switch is only intended to help prevent the taste from degrading over time, companies are often sensitive to public perceptions that they might be tinkering with major brands. PepsiCo executives likely don’t want to call any attention to the use of artificial sweeteners in the drink either.

“It’s not like a light switch. It’ll start appearing as shelf space clears,” said PepsiCo spokeswoman Andrea Canabal, who also noted the new mix will be more widely available in the coming weeks. Canabal said the company is planning a major ad campaign that will include a new logo with a heart and the theme “Love Every Sip.”

In addition to aspartame, cans of Diet Pepsi found in New York, Omaha, Neb., and the Bay Area now list acesulfame potassium as an ingredient. The ingredient is often used in combination with other artificial sweeteners and can be found in a wide range of foods including baked goods, chewing gum and gelatin desserts.

John Sicher, editor and publisher of the industry tracker Beverage Digest, said the synergistic effect of mixing the two sweeteners is intended to help keep the drink's sweetening power at a constant level, making it taste fresh longer.

"A change in sweetener does not change the flavor," he noted.

PepsiCo said in a statement Sunday that it was adding a "very small amount" of acesulfame potassium "to ensure consistency with every sip." The sweeteners used in Diet Pepsi vary depending on the region of the world.

For now, Diet Pepsi remains the No. 7 carbonated soft drink with 4.9 percent of the market, according to Beverage Digest. That's down from 5.3 percent in 2000. Coke remains No. 1 and Pepsi is No. 3. Still, Diet Pepsi rakes in roughly $5 billion in a year in revenue and remains one of PepsiCo's biggest moneymakers.

According to the Centers for Disease Control and Prevention (CDC), only 14 percent Hispanic adults consume diet drinks. However, diet drink consumption increased for both women (up to 21 percent in 2010) and men ( up to 19 percent in the same period).

Based on reporting by The Associated Press.

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