a
thiol protease which comes from
pineapple cores and stems,
kiwi fruit,
papaya, among others. This
enzyme is the reason you shouldn't add juices from these fruits to
Jell-O; if you do, the mixture will never
set, no matter how long you refrigerate it. Why? Well, the thing that makes Jell-O, gel, is
gelatin, which is a
protein that has the ability to hold large amounts of water; when it is broken down by the bromelain, it loses this ability.
In medicine, bromelain is a non-steroidal anti-inflammatory agent (like aspirin and naproxen). In other areas of food, it (and other proteases, like papain) is used as a meat tenderizer, and in brewing, to make beer less cloudy. (The cloudyness is usually caused by proteins in suspension; break them down, and voila, clear beer!)