Gelatin is processed collagen that comes from the joints of animals. Collagen is a stable protein consisting of a triple helix - three polypeptide chains wound around each other. When gelatin is mixed with hot water, the triple helix structure unwinds and the chains separate becoming random coils that dissolve in the water. As the dissolved gelatin mixture cools, the collagen forms a matrix that traps water; as a result, the mixture turns into the jiggling semi-solid mass that is recognizable as Jell-OTM. The directions on a box of gelatin include the following: "Chill until slightly thickened, then add 1 to 2 cups cooked or raw fruits or vegetables. Fresh or frozen pineapple must be cooked before adding". If the pineapple is not cooked, the gelatin will not set properly.
Pineapple belongs to a group of plants called Bromeliads. Pineapple contains a protease called bromelin. Proteases hydrolyze peptide bonds.
Explain in about 3 sentences why pineapple must be cooked before adding to gelatin.