This is a range of investigations based around the Briggs-Rauscher oscillating reaction to look at antioxidant levels in fruits and teas (though the method can be adapted for any antioxidant).
The reaction mixture cycles from blue through yellow to clear and back to blue again. The change to blue is very sudden – like the 'iodine clock'.
Once the cycle is established, add the 'antioxidant' solution immediately the solution goes blue and time how long it takes for the next one to appear.
The more antioxidant activity, the greater the delay.