Track fat breakdown with a colour indicator
Fatty acids released during milk-fat hydrolysis can reduce pH and change an indicator. A no-enzyme control is essential because enzyme formulation can itself affect pH.
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.
Lipase in nature
Lipases hydrolyse ester bonds in fats. Digestive lipases help animals use dietary lipids, while microbial lipases allow fungi and bacteria to use fats in their surroundings. The liquid S&T product linked here is an alkaline detergent lipase, not a food ingredient for this practical.
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
Detergent lipases help remove fatty soils. Other lipase preparations are used in food processing and biocatalysis; the formulation and grade must match the application.
Experiment overview
Fatty acids released during milk-fat hydrolysis can reduce pH and change an indicator. A no-enzyme control is essential because enzyme formulation can itself affect pH.
Equipment and materials per working group
- Full-fat milk, school-approved phenolphthalein reagent and 0.05 M sodium carbonate
- Two matched tubes and pipettes
- Lipase working dilution, matching diluent, timer and 35–40°C water bath
- Eye protection and a teacher-approved indicator procedure
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 the linked Practical Biology lipase method as the reference setup: 5 mL milk, 7 mL 0.05 M carbonate and its specified indicator addition.
- The reference uses a different lipase preparation; do not equate its 5% solution to a 5% dilution of this commercial concentrate. Pilot a 1:100 dilution of S&T stock and adjust from there.
- Add 1 mL selected working dilution per reaction. Aim for a manageable colour change after 5–10 minutes; check an enzyme-only pH blank and the no-enzyme control.
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 tubes ENZYME and CONTROL.
- Add 5 mL milk and 7 mL 0.05 M sodium carbonate to each.
- Add the same supplier-approved amount of phenolphthalein to each; both should start pink.
- Equilibrate at the chosen 35–40°C bath temperature.
- Add 1 mL selected lipase working dilution to ENZYME and 1 mL matching diluent to CONTROL, stir gently and start timing.
- Record colour at time zero, then every minute for 10 minutes.
- Compare the time to sustained fading; if a pH meter is available, record pH as an additional readout.
- Explain how fatty-acid production can change the indicator and why formulation blanks matter.
What should students look for?
Pink should fade earlier in a suitably tuned enzyme reaction than in its control.
Interpretation and troubleshooting
Keep alcohol-containing indicator away from flames. Follow local guidance for phenolphthalein. This detergent preparation is non-food grade; no tasting. If controls fade similarly, investigate pH and reagent compatibility.
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.