The purpose of aspartame in food is to reduce sugar and calories intake. And you may find it in many food, and here is a common food list that may with it:

Carbonated soft drinks
Powdered drink
Instant coffee and tea beverages
Fruit juice
Tabletop sweeteners
Dairy products
Frozen desserts, puddings
Yogurts
Chewing gum
Breath mints
Candy
Cereals
However, it cannot be used in cooking or baking as aspartame is not stable and will hydrolyze (break down) into amino acids in heating temperature above 80 degree. Other artificial sweeteners (e.g. sucralose, acesulfame k, sodium cyclamate, sodium saccharin, neotame) and more stable and so that they can be used in this field.

Sugar is often used as the sweetener in the traditional food, but with the disadvantages of causing obesity, cardiovascular diseases, dental caries, harmful to diabetics and other health problems. Having realized such side effects, many people are very sensitive to the sucrose content in foods, and thus turn to sugar free and low-calorie foods.

The function of aspartame is as a sugar substitute. It is about 200 times sweeter than sugar. And its calories can be ignored as the amount needed to make people feel sweet is so small, although one gram of aspartame has about 16.72 kJ calories.

Carbonated soft drinks
The uses of aspartame in carbonated beverages are in the first place of its total applications since first introduced in the early 1980s. Sucrose and high fructose corn syrup are the primary sweeteners used in traditional carbonated soft drinks.

Pepsico
Coca-Cola and Pepsi both use Aspartame in their diet coke, but Diet Pepsi was aspartame-free in the U.S. market in 2015 and used sucralose and stevia as replacements per some customers’ claimed that aspartame was not safe in 2015 (2). However, it relaunched Diet Pepsi with aspartame due to the sales sharp decline in 2016. (3)

And now we can see sucralose and acesulfame k are the primary artificial sweeteners than aspartame in its beverages. (4)

Aspartame is also used in Diet Mountain Dew. (5)

Coca-Cola
The purpose of aspartame in Coca-Cola’s drinks is to provide less sugar and fewer calories, while offering great tasting beverages.

The following common drinks contain aspartame except Coca-Cola Classic taste which is sweetened with either high fructose corn syrup or cane sugar (6):

Coke Zero Sugar
Diet Coke
Fanta Zero
Sprite Zero
The stability of aspartame in water is mainly determined by the pH value. It is most stable when the pH is 4.3 at room temperature. Since the pH of most beverages is between 3 and 5, so aspartame in beverages is very stable.