JellO packages warn you not to put pineapple chunks into the gelatin. Jello is a protein mesh with trapped pockets of liquid; the bromelin cuts the protein chains and keeps the gelatin from jelling properly.
Why do pineapples produce an enzyme that tenderizes meat? It's a defense mechanism. The sap of the pineapple plant contains much higher concentrations of bromelin and can cause severe pain if eaten.
Dr. Ron Rusay has written a simple experiment to demonstrate protein degradation's role in kitchen chemistry.
Author: Fred Senese firstname.lastname@example.org
Copyright © 1997-2010 by Fred Senese
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Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/consumer/faq/print-pineapple-jello.shtml