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Biochemistry Lab: Testing Foods for Organic Compounds.

What types of organic compounds are contained in the foods we eat? Sometimes an old idea is still the best way to teach a concept.  That is how I feel about this lab, "Testing Foods for Organic Compounds."  I have been doing this lab for over 30 years, and I never tire of doing it.  Granted, it is a bit messy and the observed results are sometimes a little subjective, but my students always love these two days in the lab.

This lab is best used during your units on Biochemistry and the Organic Compounds.  Teaching the characteristics of carbohydrates, proteins, and lipids can be dry and tiresome to students, and this lab is a great way to break the monotony of lecturing on these topics.  This lab activity is a two-part activity.  First, students will learn the indicator tests for sugars, starches, proteins, fats, vitamin C, and salt using known solutions.  Once the students understand how to complete these tests, they will test a wide variety of foods to see what compounds are contained in each food.

Before any testing of foods is carried out, students must "practice" to learn the indicator test for each compound.  For example, in order to determine if milk contains simple sugars, students must know how to carry out the test for simple sugars.  This is the purpose of the first part of the lab.  Students are given known solutions so that they can see what the positive test for a particular compound looks like.  Then, when the foods are tested, the students will recognize and understand the results they are getting.  Students will learn the positive and negative tests for the following:

  • Students will test for starch using iodine.
  • Students will test for simple sugars using Benedict's solution.
  • Students will test for proteins using Biuret reagent.
  • Students will test for lipids using the brown paper test.
  • Students will test for the presence of vitamin C using indophenol.
  • Students will test for salt using silver nitrate.
Please note: Obviously, salt is not an organic compound.  However, it is a fun test for the students to carry out, and it provides interesting information about the foods we eat.

Once students know how to use the above indicators, the real fun can begin! Choose a variety of foods that you would like for your students to test.  While you can theoretically use any foods in the experiment, some are easier to test than others.  For example, students will probably be frustrated if you ask them to test dark purple grape juice.  They simply will not be able to see the results of the tests.  I have the best results when testing the following:  Milk, yogurt, egg whites, egg yolks, potatoes, celery, cereals, and an assortment of fruit juices.  The liquid foods can be used straight from their containers.  For solids foods, you will need to prepare a solution of the food using a blender.

What are the benefits of doing this lab?
  • First and foremost, it is just plain FUN!  If students love your lab activities, they will be excited about your class.  These days, having your students excited about your class solves a host of other problems.
  • This lab reviews and reinforces the concepts you have been teaching in your classroom.  Facts about the macromolecules are easier to learn and remember when the students see a practical application of the information.
  • This lab teaches good lab techniques, how to organize data, and how to work in cooperative learning groups.
  • Students lean that a particular food that they thought was "healthy" is really nothing more than sugar and salt.
  • Working through detailed lab procedures teaches a student to read, understand, and follow directions.
  • Students must use their critical thinking and problem solving skills.

Below you can see the lab handouts that I use with my students.  Clicking here or on the image below will lead you to this lab in my TpT store. Complete teacher guide is included that contains an answer key to all questions, directions for preparing the solutions, and tips and suggestions for the successful completion of this lab activity.