It's a glycoprotein called miraculin, a naturally occurring thing. It still freaks me out every time I eat it, but it has a unique ability to mask certain taste receptors on your tongue, so that primarily sour taste receptors, so normally things that would taste very sour or tart, somehow begin to taste very sweet.
Ainda me assusta cada vez que a como, mas tem a capacidade única de esconder certos recetores do sabor na nossa língua, de modo que os recetores do sabor amargo, as coisas que normalmente teriam um sabor muito amargo ou ácido,