This week we also learned why Jell-O does not set when certain fresh fruits are added. Often on boxes of Jell-O there is a warning to not add fresh pineapple, kiwi, or papaya. We set up a few experiments to investigate why this is the case. Annie, Jocelyn and I made orange Jell-O with fresh versus canned pineapple, and Sarah and Amy made orange Jell-O with fresh versus canned (applesauce) apples. Each group set up 4 petri dishes: Jell-O with fresh fruit, Jell-O with canned fruit, Jell-O with water (control), and Jell-O with a reduced amount of water (second control). The Jell-O made with the fresh fruit did not set at all as expected! We learned that some fruits contain protein-ingesting enzymes that break down the gelatin chains into short fragments, thus preventing the gel from setting! Cooking the fruit beforehand breaks down these enzymes so that they cannot destroy the gelatin proteins. I had known that you were not supposed to put some types of fruit in Jell-O, but I never knew why.
From left to right, Jell-O with water, Jell-O with cooked pineapple, Jell-O with fresh pineapple (which became kind of frothy)
