Lactase Breakdown of Lactose

Students use over-the-counter lactase and a lactose solution to show that lactase hydrolyzes lactose into glucose and galactose. Glucose test strips provide an easy color readout to confirm glucose formation.

1. Prepare a 2 to 4 percent lactose solution in tap water or use lactose-containing milk diluted 1 to 1 with tap water to reduce opacity.
2. Label two test tubes: Enzyme and No Enzyme.
3. Add 5 mL of lactose solution to each tube.
4. Crush a lactase tablet and dissolve a small portion in 5 mL of tap water to make a lactase solution.
5. Add 1 mL of lactase solution to the Enzyme tube and 1 mL of plain tap water to the No Enzyme tube.
6. Mix gently and incubate both tubes at about 37 degrees C for 5 to 10 minutes. If no water bath is available, hold the tubes in warm hands for several minutes and extend the time.
7. Dip a glucose test strip into each tube for the time specified by the strip instructions. Remove, wait the indicated development time, and compare to the color chart.
8. Record whether glucose is detected in each tube and note the relative intensity of color.
9. Interpret results: appearance of glucose in the Enzyme tube but not in the No Enzyme tube indicates that lactase converted lactose into glucose and galactose.

Lactose Enzyme Examination - Dan Rott:

📄 Explore enzymes and the science of lactose intolerance using lactase tablets - Science in School: https://scienceinschool.org/article/2024/science-of-lactose-intolerance/

• Test different incubation temperatures, such as room temperature versus 37 degrees C, to explore temperature effects on enzyme rate.
• Compare different lactase tablet brands or doses to see how enzyme amount changes the readout.
• Use lactose-free milk as an additional control; it should already contain glucose and give a positive strip without added enzyme.
• Extend incubation time and take multiple readings to create a simple time course of glucose formation.

• Do not ingest any reagents or solutions; treat all student-handled samples as not food.
• Wear eye protection when crushing tablets and handling warm water baths.
• Avoid hot water above 45 degrees C to prevent burns and to avoid denaturing the enzyme unintentionally unless testing temperature as a variable.
• Wash hands after the activity and clean the workspace; dispose of used strips and solutions according to classroom guidelines.

• Why is a No Enzyme tube included as a control? (It shows that any glucose detected comes from enzyme action, not from the lactose solution itself.)
• What products are formed when lactase acts on lactose? (Glucose and galactose.)
• Why do we incubate near 37 degrees C? (It approximates the optimal temperature for many human-use enzymes, increasing reaction rate without denaturation.)
• If the glucose strip is positive in both tubes, what could explain this? (The starting solution already contained glucose, the lactose source was lactose-free, strips were contaminated, or instructions were not followed.)
• How would very hot water affect your results? (Heat can denature lactase, reducing or eliminating glucose formation and giving a weaker or negative strip.)