STUDIES ON INHIBITION OF MUSHROOM POLYPHENOL OXIDASE USING CHLOROGENIC ACID AS SUBSTRATE

The inhibitory effects of aromatic acids of the benzoic, cinnamic, and phenylalkanoic series on the enzymatic activity of a commercial purified mushroom polyphenol oxidase (PPO), using chlorogenic acid as a substrate, were determined by spectrophotometric and polarographic methods. The I50 values obtained were higher when determined by the polarographic method. Hydroxylation and methylation of the benzene ring as well as the addition of a second methylene group adjacent to the carboxylic acid decreased the inhibitory effect. Aromatic acids of the benzoic and cinnamic series appeared to have, respectively, an irreversible and most often a reversible inhibitory effect on PPO activity. The results also showed that the aromatic acids exhibited noncompetitive, mixed, and uncompetitive types of inhibition, with a range of K(i) values varying from 0.26 to 56.7 mM. Spectrophotometric and polarographic methods failed to determine the type of inhibition for protocatechuic, caffeic, hydroxyphenylacetic, and hydroxyphenylpropionic acids. Benzoic, o-coumaric, m-coumaric, ferulic, phenylacetic, and phenylpropionic acids demonstrated different types of inhibition depending upon the method used. The results indicated that the type and degree of inhibitory effect of aromatic carboxylic acids are dependent upon both inhibitor and method used.