| MadSci Network: Chemistry |
Jell-O is the brand name for a flavored gelatin from Kraft. To understand gelatin, let's start with where it comes from.
Collagen is a protein that can form long ropes called fibers, which give strength and durability to skin, bones, muscles, and most of the body. Each single "piece" of collagen is made up of three long strands of protein. If collagen is boiled, these strands separate from each other, but then when they cool, they can't fit together properly to reform the collagen. This process of changing the shape of a protein such that it cannot function properly is called "denaturing". Gelatin is denatured collagen.
Because the long strands of gelatin were once together as a strand of collagen, they still have some strong attractions toward each other, so when they cool down, they will try to bind to each other. But, since heating them also mixes them up, the strands of gelatin are not lined up next to each other, so one part of a strand will bind one strand, and another part will bind another strand. Expanded out to millions of strands, this produces a 3-Dimensional web of long protein strands sticking to each other (for more depth, click here).
Essentially, the gelatin is trying to become a solid while it is still in solution. This is not so much a chemical change as a phase change (liquid to solid), since you can reheat the gelatin and it will become a liquid until it cools again and returns to its semi-solid state.
My heroes, Beakman and Jax, at "You-Can" have a similar explanation of gelatin, although their diagram of how gelatin forms is more applicable to Agar (formerly agar-agar), which is a carbohydrate (not a protein), like corn starch or cellulose, with lots of branches which make it look spiky. Agar is similar to gelatin in so far as they both form gels, but that is where the similarities end. In the lab, we use agar in Petri dishes to grow bacteria, because bacteria can eat gelatin and move around on the plate, but they can't eat agar, so they pile up on top of each other to form a nice colony.