4 Lab 3. Chemistry of Food
Lab 3. Chemistry of Food
OBJECTIVES
- Test for various biological macromolecules in food and observe how enzymes can break them down.
- Investigate the behavior of lipids, and use soap to mimic the action of bile.
PRELAB
Read the lab AND consult the textbook to answer the questions (include in lab notebook):
- Covalent bonds occur when atoms share…
- Building a molecule from simpler components is called anabolism. Breaking a substance down is called…
- The protein in gelatin that allows it to form a gel is called…
- An enzyme in pineapple capable of digesting the protein in gelatin is called…
- For each of the following substances, identify whether it is a carbohydrate, lipid, protein, or “other”.
- vegetable oil
- lactase
- amylase
- starch
- lactose
- distilled water
- Each of the following statements applies to one of the tests we will perform in this lab. Give the name of the appropriate test.
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- Uses strips that change color in the presence of the test substance
- Requires that the test solution be heated
- A very dark colored solution indicates that a lot of starch is present
- If the lactase enzyme is effective in breaking down lactose, would you expect to see a positive or negative result for the glucose test (“positive” = glucose is present)? Explain.
- If the amylase enzyme is effective in breaking down the cracker, would you expect to see a positive or negative result for the presence of starch? Explain.
INTRODUCTION: Testing foods for carbohydrates, lipids, and proteins
Carbohydrates, lipids, and proteins are relatively large molecules that play many important roles in living organisms. Carbon atoms and the many covalent bonds they can form provide the basic framework for all of these macromolecules. In lab today, we will use a suite of chemical tests to detect the types of molecules present in various food items and how enzymes affect them.
Carbohydrates come in several basic forms. The simplest sugars are called monosaccharides, and they contain 3-7 carbon atoms, often bonded together in a ring structure. Glucose is a very common 6-carbon sugar. When two monosaccharides bond together, they form a disaccharide, such as sucrose. Many monosaccharide subunits bonded together forms a polysaccharide, a much more complex carbohydrate. Starch, cellulose and glycogen are common examples of polysaccharides. Our test methods will allow us to easily detect starch and also reducing sugars (detected as copper is reduced to give a red color). Glucose and fructose should test positive, but sucrose (a disaccharide) may not (unless it is broken down by heat or acid).
There are many different types of lipids. They are all grouped together as lipids because at least some part of the molecule does not dissolve in water. Oil and vinegar salad dressing requires vigorous shaking, because the oil and vinegar (which is a water-based solution) do not mix well. We will use a simple test to help determine whether or not lipids are pr