Hi everybody,
Finally, i 've collected a branch from the tree and i get advice from a botanical expert. We have checked from the IRD herbarium collection in Cayenne and fruit/leaves could come from Helicostylis pedunculata. Probability is near to 90%.
The only thing that disturb me is the fruit size. H. pedunculata should have fruit size up to 1 cm in diameter, and the ones i've collected are more bigger (all were 2 to 4 cm wide).
I managed to get ripe fruits with my shotgun, and i tasted them : They are delicious, hard to describe but pulp is sweet and the very thin skin is slightly acid. There are only 3 to 4 seeds in one fruit so there is a good amount of stuff to eat.
Unfortunately, there are a lot of worms in the fruits, far more than in a guava.
I'm really happy to have found this specie.
Many thanks for those who helped for this fruit identification.