My guess is that these turnips just have really low peroxidase activity because the H2O2 and guaiacol were made up fresh the day of the labs. Thanks in advance for your help or advice. It's the problem of common names in different parts of the country refer to different beasts. Other than that, I can't think where you may be having problems, since your recipe looks correct. MA 01063 Rosemary, We do this experiment every semester in our majors course and its beautiful.
Turnips really do vary quite a bit.
Sometimes it takes a fraction of 1g per 100ml sometimes as much as 5-6g per 100ml. Maximum activity comes from using the skin and not just the inside of the turnip. Be sure you are grinding it in ph 7 buffer or you will have problems. Try using a buffer solution. If your lab uses pH as a variable, extract it in 0.01 M phosphate and use 0.1 M for the experiments- that way the enzyme will be protected but can still be changed to the experimental conditions.