From the Super Mario Wiki
Donkey Kong 64
During the opening sequence, King K. Rool orders the Kremlings to steal the Golden Bananas and kidnap the other four Kongs (who are later freed) in an attempt to distract Donkey Kong while they repair the Blast-o-Matic. B. Locker is assigned by K. Rool to block the Kongs from entering the other worlds; however, B. Locker allows them to enter if they have at least a minimum of a certain number of Golden Bananas (the requirement is different for each world).
During their adventure, Donkey Kong and the four other Kongs (Diddy Kong, Tiny Kong, Lanky Kong, and Chunky Kong) must collect Golden Bananas in every world, by completing various tasks and challenges. There are 25 Golden Bananas in every world, five for each Kong to obtain. There are a total of 200 Golden Bananas to collect in the seven worlds and the hub location, DK Isles.
Tiny can obtain a 201st Golden Banana from the Banana Fairy Princess when she and the Kongs have captured every Banana Fairy. This Golden Banana is hidden behind a door, which the Banana Fairy Princess opens if the Kongs have recovered every Banana Fairy. This Golden Banana is different from other ones because of its larger size, and it has the Rareware logo on it. All 201 Golden Bananas are required to achieve a 100% completion rating and to unlock the secret ending.
Donkey Kong Country Returns
In Donkey Kong Country Returns, a single Golden Banana makes an appearance. While leaving Cranky Kong's Shop, Cranky Kong can sometime ramble about finding a Golden Banana that transports one to another dimension. After accessing the Golden Temple via the Rare Orbs, Donkey Kong and Diddy Kong are surprised to see the giant Golden Banana, held by two golden DK-like statues. Peeling its skin and tasting it does indeed transport them to another world.
Mario Kart Arcade GP DX
Donkey Kong Country television series
The animated series features a single Golden Banana of a different type in the episode "Raiders of the Lost Banana". This Golden Banana is found by DK in Inka Dinka Doo's Temple, and he decides to give it to Candy Kong as a present. As a result, however, DK sets off a curse that befalls anyone nearby the beholder. K. Rool later kidnaps Candy and demands she hand over the banana, but DK shows up to rescue her and returns the Banana to Inka Dinka Doo. However, Polly Roger then steals the banana back, but now only K. Rool is affected by the curse.