1. Set up water baths with 400 mL water in beakers with different temperatures range from around 10 degree to 70 degree.

2. Incubate equal volume of Aspergillus amylase (1%) (Tube A) and starch solution (added with iodine solution, Tube B)  in different water baths for 5 minutes.

3. Take normal speed and time lapse videos.

4. After five minutes, mix tubes A and B in each water bath and record the time taken for decolourization of blue-black starch-iodine complex (t).

5. Plot a graph of the effect of temperature on the amylase activity (1/t).

N.B.

• Aspergillus amylase is still active at 80 degree, according to our results.  Normal speed video is needed to take the decolourizing time as colour changes very fast.

• Time lapse video is suggested to record the colour change at lower temperature.

1. Set up water baths with 400 mL water in beakers with different temperatures range from around 10 degree to 70 degree.

2. Incubate 1% porcine pancreatic lipase, bromothymol blue and sodium carbonate  in different water baths for 5 minutes.

3. Take time lapse videos.

4. After five minutes, add 2 mL full fat milk to each test tube  and record the time taken for change in the colour of bromothymol blue from blue to yellow (t).

5. Plot a graph of the effect of temperature on the amylase activity (1/t).

N.B.

• Full fat milk contains emulsified milk fat droplets, which act as the substrate of lipase.

• Lipase catalyse the hydrolysis of triacylglyceride to fatty acid and glycerol.  Fatty acid lowers the pH and therefore bromothymol blue changes from blue to yellow.  The end point can be determined by the playback of the time lapse video, which can show the time taken for the indicator to change to yellow completeley.

In order to determine which indicator is more suitable for detecting the lipase activity, different pH indicators were used:

1. Add equal amount of lipase and sodium carbonate solution into test tubes.  

2. Add equal volume of pH indicators (from left to right: bromophenol blue, bromothymol blue, litmus blue, methyl organge, methyl red, phenolphthalein, phenol red, universal indicator and phenolphthalein (no lipase added)).

3. Take time-lapse video to record the colour change.

N.B.

• The range of pH for the colour change of pH indicator can be checked in this web site.

• Phenolphthalein is the best one as it changes colour from pH 8 to 9.  But its colour is too pale to determine the end point easily.

• Instead, bromothymol blue shows a conspicuous colour change from pH 6-7.6.  Therefore we usually use bromothymol blue as the pH indicator to test for rate of lipase activity.

During the COVID pandemic period, the lesson times are shortened and it is difficult to do some tests that usually take longer time to get the results.  Students can use time lapse video to take the results and therefore the normal lesson time is not seriously affected.  Time lapse video can also provide evidence of students' work and sudents can replay the video to get raw data for the analysis of data.

According to our experience, the following practices may be essential:

1. Many mobile devices have built-in time lapse recording function.  

2. A tablet more mobile phone stance is very important to fixed the mobile device, as shown in the Figure A, which shows the use of two iPads to take video, one for time lapse video, one for normal speed video.  The normal speed video is used to capturerapid change in colour of enzymatic reaction.

3. The iPad stance can be bought from computer accessory shops.  If it is not available in the school, the mobile device can be supported by protection case and the positiion can be adjusted with a chemistry lift table (Figure C), as show below.  Sometimes, the tablet computer can also be fixed in positioin with the support of protection case and a rim of A4 paper, as shown in Figure E.

4. We need a timer to diaply the time.  We used stopwatch originally (Figure C and D).  However, the time may not be displayed properly sometimes and we suggest to use another mobile device to display the time (Figure A).  If water bath is used, as in the case in Figure C, the stop watch can be put in a sealable plastic bag.

Sample of Canva Presentation

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