Class time: 30-50 minutes.
Purpose: Students can use three different types of assays to test a variety of foods for the presence of lipids, or fats. In addition, students may research the types of fats that foods contain and relate their findings to dietary health.
Notes to the teacher: Feel free to scale this activity up or down, depending on your class time and the level of your students. You might tell students a day or two in advance that they can bring in their own foods to test. Student interest will likely be heightened if they are testing their own food.
Emphasize the importance of doing additional assays in tubes without food as a negative control.
As a further chemistry-based exploration, have your students measure the amount of saturated vs. unsaturated fat by titrating different oils with an iodine solution (to determine the iodine number). Amrita Vishwa Vidyapeetham University provides a virtual lab example here.
Another option for developing a slightly more inquiry-based lab is to choose the oils or foods for your students (picking similar-looking foods) and have students determine the food type based on fat content.
Also, feel free to remove the anticipated results and interpretation of each assay test, and have students interpret their results within their lab group.
Potential Food Materials (choose or have students choose 10 foods):
- Vegetable oil (can be considered a positive control)
- Skim milk
- 1% fat milk
- 2% fat milk
- Whole milk
- Ice cream
- Nonfat yogurt
- Bacon or other meats
- French fries
- Apple juice
- Peanut butter
- Green peas
- Sunflower seeds
- The Activity Guide for Students
- Lab goggles
- Solid and liquid foods to test for lipids (or students can bring their own — see above list)
- Bowls for foods
- Access to a microwave (for melting butter and getting fatty liquid from meats, cheese, etc.)
- Assorted tools, such as spoons or mortar and pestle for scooping, grinding, mincing or smashing foods
- Test tubes (at least a dozen per student lab group)
- Caps or stoppers for test tubes
- Test tube racks
- Weigh paper/foil/plastic boats
- Alcohol (91% isopropyl rubbing alcohol from the drug store or grocery store)
- Water (distilled water is ideal, or you can use tap water if it has a fairly normal pH and not many impurities)
- 10 ml-graduated cylinders or pipettes for measuring small volumes of alcohol, water and liquid foods
- Sudan III stain (one bottle per lab group, $4.50 for 15 ml-bottle at Home Science Tools)
- Q-tips (at least a dozen per student lab group)
- Paper for grease spot tests (plain brown paper bags are ideal, or regular printing paper also works)
- Hair dryers (optional for speeding up the drying process)
- Markers to write on the test tubes and paper