Microbial esterase assay - Microbial esterase assay (May/25/2002 )

I am looking for a quick and easy method of quantifying microbial esterases.
I have tried fluorescein diacetate but have had a lot of solubility problems, if anyone knows of a method with this compound it would be appreciated.
I have also tried para-nitrophenol compounds but they seem to lack the specificity for microbial esterases.
Any suggestions gratefully recieved.

I used para-nitrophenol compounds (C2-C12) and found huge differences in specificity for some esterases.
A simple old fashioned method is preparing plates containing 3ml of an emulsion of 50% tributyrin and 5% gum arabic per 100 ml of medium. You will get turbid plates, grwoth of esterase containing bacteria will form a clear halo around the colony.