3,4-Dihydroxyphenylalanine gel diffusion assay for polyphenol oxidase quantification.

We have developed a simple, inexpensive plate assay to detect and quantify polyphenol oxidase (PPO) activity from different origins. The logarithm of enzyme activity is linearly correlated with the diameter of the dark, l-3,4-dihydroxyphenylalanine (l-DOPA) oxidized circles produced in the gel, thereby allowing quantification of PPO. Moreover, precision and high reproducibility of the assay were confirmed by statistical analysis.