Don't forget that you have a quiz over Sections 2.1-2.3 on August 29.
Download this lab writeup.
Useful Links: Testing for proteins, lipids & carbs
You need to develop a research question and construct four hypotheses (because you're doing four tests).
Different foods change color when indicators were added to denote the presence of macromolecules. Why does this happen? To understand this phenomenon, you need to be able to describe the structures of carbohydrates, lipids and proteins and explain why they behave in the way that they do when exposed to certain indicators. This information will be presented in your Introduction.
Background Knowledge. Take a look at this interactive link. It describes the six functional groups. What is important for you to understand is what happens during the complementary processes of hydrolysis and dehydration. Another important fact is to understand what happens when electrons are donated by one molecule and received by another. Molecules that donate electrons are called reducing agents and molecules that receive electrons are reduced.
You will be testing mainly for the presence of simple carbohydrates (glucose, sucrose), complex carbohydrates (starch), and proteins. Below are the indicators you will use to detect for these macromolecules.
Benedict’s reagent changes color when exposed to a reducing agent, and all monosaccharides are reducing agents. Some disaccharides (like sucrose) have no free carbonyl groups and thus are non-reducing agents. Samples have to be put in a water bath for at least two minutes before you can see the color change.
Biuret's reagent changes color in the presence of proteins because the copper II ions form a complex with the nitrogen atoms. The color change ranges from blue to violet, and the more peptide bonds present, the more violet the color change.
Iodine solution is good for identifying the presence of starch because iodine atoms can fit inside the helical structure of starch compounds and change the color from dark blue to black.
We don't have Sudan IV. The way you'll test for the presence of lipids is to drop the sample into a test tube full of water. A layer should form if a lipid is present.
If you want to know more (including the overwhelming biochemistry of it all, go here and here.
Here is a video that shows how your testing should go. We will be running a known test and an unknown test. You will know what the samples are in the known test, obviously. You will NOT know what the samples are in the unknown test.
There are three unknowns: MIX, MAX, AND MOX. You will test for the presence of a starch, a sugar, and a simple sugar. So this means you will need to rinse your test tubes out after each test and refill from the sample bottles.