McMush

Before the Thanksgiving break we did a lab that had a definite gross-out factor, called McMush.  This lab allowed students to use various reagents to test food samples for some of the macromolecules we have been studying in class.  We began the lab with known solutions of glucose, starch, protein, and oil (lipid).  For each macromolecule, students did a test with a reagent on the known solution to determine what the positive result would look like, and compared this to a test on water which we know does not contain any of the macromolecules.  Students then recorded the results for a positive and negative test for each molecule.  They found that Biuret solution causes a dark violet color in the presence of proteins, that Benedict's solution and heat causes a white and then orange color in the presence of glucose, that iodine causes a dark purple/black color in the presence of starch, and that Sudan III stains the oil which then forms a red layer on top of water.

Getting the test tubes set up!

Students compare known positive and known negative samples to observe the effects of the reagents.

A student adds Benedict's reagent to a carbohydrate solution.

After obtaining this new knowledge about how various reagents react with macromolecules, students were ready for the "fun" part.  Before beginning the lab, I had ground up a McDonald's Happy Meal (minus the toy) in a blender for several minutes.  I made a big show of putting the different parts of the Happy Meal into the blender- first the cheeseburger, which I broke up into smaller pieces before adding the the blender, followed by french fries, apple slices, and finally the drink- chocolate milk!  Once everything was added, I blended it all together for several minutes to make a goopy liquid that we called "McMush!"  Each student lab group measured out four small portions of the McMush to test for four different macromolecules- simple carbohydrates, starch, protein, and lipids.  Students used the same four reagents from the earlier tests, since they now knew what a positive test for each macromolecule would look like.  It was fairly gross, but I think most students got a kick out of it!

The McMush after it has been blended!

As you might expect, we found that the McMush tested positive for all four macromolecules.  We discussed how the simple carbohydrates likely came from the apples and the chocolate milk, that the starch likely came mainly from the french fries, that the protein mainly came from the hamburger patty and the chocolate milk, and that the lipids came from the burger and the fries.  We discussed how the reagents we used in this lab can be used for testing foods for various molecules in many situations, including when people have special diets that require them to consume or avoid consuming particular things.  We connected this to patient case studies we have been working on in class that involve individuals whose symptoms are related to the various macromolecules in their diets, casuing disorders such as lactose intolerance, celiac disease, and diabetes.  We also discussed how we did not test for the fourth macromolecule, nucleic acids, because these molecules (DNA and RNA) are not nutrients we get from foods the way carbs, lipids, and many proteins are.  All in all, a fun and educational way to spend the last few days before the break!