Cats cannot perceive sweetness.

No wonder they can be so bitter. Studies have shown that domesticated cats are neither attracted to nor show avoidance of the taste of sweet carbohydrates and high-intensity sweeteners. Recordings from cat taste cells have shown no response to sucrose and several other sugars.

Other than this, a cat’s sense of taste is similar to most other mammals’. Dogs on the other hand prefer natural sugars, e.g. sucrose, glucose, etc. This of course may serious implications for the biological community, but all it means for you is that you shouldn’t buy your cats’ treats based on sweetness, because as with most things, cats are indifferent to it. 

(Source)