Answer in the comment section.

Answer: Bananas contain an atom called Carbon-14. A radioactive chemical that, every 72 mins,
emit a positron. Which is a counterpart of..... uhhhhh....... electrons.......idk exactly.

It's actually because of the potassium-40 in the banana. Positrons are just weird electrons. Electrons have a negative charge, but positrons have the same mass as an electron, but the same charge as a proton.

It's just the decay of the potassium-40. (Humans also do the same thing)

Oh.