Reveal the sugar in lactose
Treat a defined lactose solution with enzyme and use glucose-specific test strips to reveal a product. Milk can be an extension after its baseline glucose and matrix effects have been checked.
Use these original S&T teaching drafts after a teacher or technician has piloted the exact product, substrate and assay. Recipes and timing targets are proposed starting conditions, not validated performance claims. Review current SDS and institutional guidance; wear eye protection, avoid enzyme aerosols and splashes, and keep powders under technician control. No tasting. Keep controls at the same final volume, pH, temperature and stirring conditions. Plan reagent-specific waste disposal.
Lactase in nature
Lactase is a β-galactosidase. In the human small intestine it helps split the milk sugar lactose into absorbable monosaccharides. Microorganisms also possess β-galactosidases, allowing them to use lactose. Commercial lactase is not harvested from the human digestive system.
What chemical reaction does it catalyse?
Enzymes speed up a reaction without being consumed in the overall process. The preparation, accessible substrate and reaction conditions determine what you can measure.
Industrial applications
Lactase is used for lactose-reduced dairy products and lactose conversion in processing. A short positive glucose test does not establish that a milk sample is lactose-free.
Experiment overview
Treat a defined lactose solution with enzyme and use glucose-specific test strips to reveal a product. Milk can be an extension after its baseline glucose and matrix effects have been checked.
Equipment and materials per working group
- 1% w/v lactose solution; three tubes
- Liquid lactase, matching diluent, pipettes and timer
- Glucose-specific test strips approved for the sample matrix
- A low-concentration glucose standard within the strip range
- 37°C water bath and eye protection
Plan a class of 30
Use 10 working groups of three. Multiply the per-group quantities in this guide by 10, then allow an appropriate preparation reserve. Keep concentrations unchanged when scaling. Assign a timer, a practical operator and a recorder, then rotate roles. Set up teacher-prepared comparison samples in advance where a reaction takes longer than the lesson.
Teacher and technician preparation
- Use lactose near pH 6.0 and trial compatibility with this lactase preparation.
- Pilot 0.1–0.5 mL liquid enzyme per 5 mL final reaction; start at 0.1 mL. Bring all reactions to the same volume with diluent.
- Check that enzyme alone gives no substantial glucose-strip signal and that the positive standard is detected. Use the strip manufacturer’s reading time.
Use enough working enzyme to make a clear comparison in the intended time window. Do not automatically add more concentrate: reactions can finish before measurement, stocks can alter pH or background colour, and some substrates remain slow even at a high dose. Pilot the proposed recipe, then record the final preparation and dilution on the results sheet.
Step-by-step class method
- Label ENZYME, CONTROL and ENZYME BLANK.
- Put 4.5 mL lactose solution in each of the first two tubes and 4.5 mL matching diluent in the blank.
- Warm at 37°C for 3 minutes.
- Add the pilot-selected enzyme dose to ENZYME and the same dose to ENZYME BLANK. Add matching diluent to CONTROL; equalise final volumes to 5 mL.
- Test fresh samples at time zero, 5 minutes and 10 minutes, using a new glucose strip each time.
- Read each strip at the manufacturer’s stated time and compare it with the glucose standard.
- If samples exceed the strip range, use the same measured dilution for all relevant samples and repeat the test.
- Explain why glucose production supports hydrolysis but is not a direct measurement of residual lactose.
What should students look for?
A stronger glucose-strip signal in the treated lactose than both controls supports enzyme action.
Interpretation and troubleshooting
Industrial lactose removal may take hours. Treat these samples as laboratory materials: no tasting or drinking. Food-grade status does not turn a classroom practical into food preparation.
Questions for the class
- What changed in the enzyme-treated sample compared with the control?
- What bond or substrate does this enzyme act on?
- Which conditions did we keep the same, and why?
- Could colour, pH, warming, stirring or background sugars explain part of the result?
- What would you measure or change in a follow-up investigation?
Your investigation sheet
Name: ____________________ Group: ______ Date: __________
Prediction: _______________________________________________________
Enzyme preparation / batch: ________________________________________
Final working dilution and dose: ____________________________________
Substrate: _______________ pH: ______ Temperature: ______ °C
| Time / min | Enzyme + substrate | No-enzyme control | Enzyme-only blank / notes |
|---|---|---|---|
| 0 | ________________ | ________________ | ________________ |
| 2 | ________________ | ________________ | ________________ |
| 5 | ________________ | ________________ | ________________ |
| 10 | ________________ | ________________ | ________________ |
| Later: ___ | ________________ | ________________ | ________________ |
Conclusion supported by our control: _________________________________
One limitation and one improvement: __________________________________
Background sources and product details
This is an original teaching adaptation. External methods establish useful principles and assay formats; they do not validate the suggested doses for S&T preparations.