I think , Sucrose, under appropriate condition is hydrolysed to glucose and fructose which are reducing sugars. This is effected by a strong acid (HCI) and may be from carbonic acid . This acid incorporate water into the, disaccharide and causes its hydrolysis into its constituent monosaccharide .

I took from this research entitled:

ESTIMATION OF SUGAR IN SOFT DRINKS

Article ESTIMATION OF SUGAR IN SOFT DRINKS

Phelan Apostol

It's not that odd to find some Fructose/Glucose in your carbonated drink as the pH of these products is mostly below 3. But for a more certain answer you can perform the experiments over a timelapse to find out whether the hydrolyzates are increasing or not.

Best.

It is well-established that sucrose in carbonated beverages hydrolyzes to glucose and fructose. As mentioned by Goetze, above, the pH is typically very low. The pH is low only in small part to the dissolved carbon dioxide. There is a significant amount of phosphoric acid in many carbonated drinks.

Also, most carbonated drinks are shipped without temperature control. Depending upon how the beverage is shipped and stored, the hydrolysis can be significantly accelerated by heat.

See Figure 5 in Monsivais, Pablo, Martine M. Perrigue, and Adam Drewnowski. "Sugars and satiety: does the type of sweetener make a difference?." The American journal of clinical nutrition 86, no. 1 (2007): 116-123. (freely available on Google Scholar) to see a time course analysis of sucrose hydrolysis.