measure lipase enzyme activity

If you’ve a couple of pH electrodes and sensors, the following is one of the most successful enzyme measurements I’ve tried. Before bothering further, connect the pH electrodes to a data logger and ensure that they give comparable readings when placed in sodium carbonate solution and also in water. Rinse them. The pH probes will be used to detect an increase in fatty acids as the enzyme lipase breaks down the fat in cream. Two pH probes allow us to compare how fast this happens with and without bile. Washing up liquid is used to substitute for ‘bile’ which helps emulsify the fat.

• You need some cream, such as the UHT pots of cream used for adding to coffee. The UHT pots last for ages and there’s little waste. With the help of the pH probes, add drops of sodium carbonate to the cream to bring it to pH 8-10. This is because the lipase we use works best at pH10. Fortunately, lipase in the gut prefers alkaline conditions too.
• Place the pH probes in two boiling tubes with 5ml of alkaline cream put these in a warm water bath. Start recording and look for a steady pH reading. Replace a probe or move away from electrical interference if you get a noisy trace. Add two drops of ‘bile’ to one tube. Finally add 5ml well-mixed, 2% lipase suspension to both tubes. (Lipase liquid from www.ncbe.reading.ac.uk is £13 a pot and it can last ages).
• Record the pH for around 30 minutes, while stirring and keeping the temperature warm. You’re expecting to see the pH drop and ultimately plateau. This can happen more quickly than expected so take notes what you’ve used for another try.