Watch starch disappear
Compare the iodine response of starch with and without amylase. Long starch chains give a dark iodine complex; as chains shorten, the sampled mixture can retain the iodine’s amber colour.
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.
α-Amylase in nature
Amylases make stored starch accessible. In germinating seeds they help mobilise food reserves; in animals, digestive amylases start the conversion of dietary starch into smaller carbohydrates. Microorganisms also secrete amylases to obtain nutrients. The S&T high-temperature preparation is microbial: its behaviour should not be assumed to match human salivary amylase.
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
Starch liquefaction, brewing, baking and biofuel manufacture use amylases to reduce viscosity and make carbohydrates available for further processing.
Experiment overview
Compare the iodine response of starch with and without amylase. Long starch chains give a dark iodine complex; as chains shorten, the sampled mixture can retain the iodine’s amber colour.
Equipment and materials per working group
- Two labelled test tubes per group, spotting tile and separate pipettes
- 0.5% w/v soluble starch, prepared and cooled by the technician
- School-use iodine reagent at the supplier-approved working concentration
- Warm water bath at 40°C, timer and eye protection
- Amylase working solution and matching enzyme-free diluent
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
- Prepare starch in compatible buffer near pH 6.0. Keep the same pH in both tubes.
- Pilot 1:100, 1:1,000 and, if needed, 1:10,000 dilutions of the actual liquid stock. Start with 1:1,000; the stock is highly active and a neat dose may finish before students can sample.
- Choose a working dilution that reaches the endpoint after roughly 5–10 minutes at 40°C. Confirm a no-enzyme control stays dark and run enzyme-only and starch-only checks.
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 two tubes ENZYME and CONTROL; add 4.5 mL prepared starch to each.
- Stand both tubes in the 40°C bath for 3 minutes before starting.
- Put separate small drops of working iodine into numbered spotting-tile wells.
- Add 0.5 mL selected amylase working solution to ENZYME and 0.5 mL matching diluent to CONTROL; mix gently and start the timer.
- At time zero and every minute, place one small sample from each tube onto a fresh iodine drop using separate sampling pipettes. Do not return iodine to the reaction tubes.
- Record whether each sample is dark blue-black, intermediate or amber. Continue to 10 minutes.
- Record the first sustained amber result and repeat the comparison if lesson time permits.
- Compare the two time courses; explain why a colour change reports starch-chain breakdown rather than measuring glucose directly.
What should students look for?
An enzyme-treated sample should lose the strong starch–iodine response sooner than its control. Record an actual endpoint; do not fill the results sheet with an expected value.
Interpretation and troubleshooting
If the reaction is instantaneous, dilute the enzyme further. If neither tube changes, check preparation, temperature and activity with a fresh pilot. This thermostable amylase need not follow the textbook temperature curve of a human enzyme.
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.
Using the complete amylase education kit?
Download the illustrated eight-page ST0226 guide for potato starch and crushed malt experiments, matched controls, six-well sampling, refractometer readings and a printable student results sheet. Teachers should pilot the reaction before class to establish a useful 5–10 minute observation window.