- Enzymes are important components of digestion because they break down large food molecules into smaller chemical subunits. One digestive enzyme, lactase, breaks down lactose (a disaccharide found in milk) into the monosaccharides glucose and galactose. Many people develop a condition called lactose intolerance as they grow older and their bodies stop producing lactase. As a result of the inability to digest lactose, these people suffer from cramps and diarrhea after consuming dairy products that contain lactose. Instead of eliminating dairy products from their diet, people who have trouble digesting lactose can usa a product that contains lactase to break down lactose in dairy products.
- In this investigation you will observe the effectiveness of a milk-treatment product that contains lactase by testing milk samples for the presence of glucose.
MATERIALS:
Milk-treatment product (liquid)*
Toothpicks
Spot plate or depression slides
Droppers
Whole milk
Glucose solution**
Glucose test strips**** Purchase enough whole milk and milk-treatment product for each lab group to have several drops of each. Commercial milk-treatment products that contain yeast-derived lactase are available from most pharmacies. Avoid the product in solid form, as it will contain glucose. One brand is Lactaid drops, which costs about eight dollars for 7 ml.
**This is to give the student a clear, strong, positive glucose test to compare to. Glucose is listed as dextrose in some catalogs.
***One brand is "Clinistix" reagent strips for urinalysis, by Bayer. These come in 50 strip boxes for about 7 dollars.
PROCEDURE:
1. Obtain a spot plate, or 4 depression slides, and label 4 wells: (a) Treated milk, (b) Untreated milk, (c) Milk-treatment product,and (d) Glucose solution.
2. Place 2 drops of whole milk in each of the wells labelled: (a) Treated milk, and (b) Untreated milk.
3. Place 1 drop of milk-treatment product in each of the wells labelled: (a) Treated milk, and (c) Milk-treatment product. Using a toothpick, stir the mixture in the well labelled: (a) Treated milk.
4. Place one drop of glucose solution in the well labelled: (d) Glucose solution.
5. Test all 4 solutions for the presence of glucose. Testing will depend on the brand of test strips you have. If you are using the Clinistix by Bayer, you will need 4 test strips (one for each of the 4 solutions). Touch the test pad on the strip to the solution being tested. After 10 seconds, compair to the color guide on the bottle. Clinistix have a negative indication, and then 3 levels of positive (light, medium, and dark). Follow the instructions for the brand you have. If you have full length test strips, use toothpicks and make test dots on the strip. You will be able to do all 4 tests on one strip. Be sure to use a clean toothpick for each solution.
RESULTS:
8. Compare your test spots to the comparison chart of the test strip instructions. Record your results on the table. The test results will depend on the brand of test strip used. Because this is a qualitative analysis, the answers can be as simple as yes glucose is present, or no glucose is not present. A unit appropriate to your brand of test strip can be used to further show the intensity of the test results.
SOLUTION TESTED:________________RESULTS OF TEST:____________
(a) Treated milk ___________________________________________________
(b) Untreated milk _________________________________________________
(c) Milk-treatment product __________________________________________
(d) Glucose solution _______________________________________________
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- In this investigation you will observe the effectiveness of a milk-treatment product that contains lactase by testing milk samples for the presence of glucose.
LACTOSE DIGESTION
By the Enzyme Lactase
INTRODUCTION: