<p>Enzymatic browning that causes losses in fruits occurs when the enzyme polyphenol oxidase (PPO) (monophenol oxidase E.C.1.14.18.1 or catechol oxidase E.C.1.10.3.1) reacts with oxygen. In this study, the interaction of PPO in red apple, banana and jerusalem artichoke with an antioxidant namely gallic acid was investigated. Gallic acid is presented in well-known database (BRENDA) as a substrate and/or inhibitor of the PPO. In order to investigate the reactions in between different concentrations of gallic acid solution (0-800 µl) with the PPO prepared, no additional substrate was added in its natural environment, and the media were analyzed by two methods. The findings of the study in a holistic way showed that the spectrophotometric and colorimetric method results of experiments of all fruits and all gallic acid concentrations studied were compatible with each other. It was observed that 50 µl stock gallic acid solution could stop the browning reaction, but when this concentration was exceeded, a different reaction which forms a green product was observed. In the study, the possible reaction mechanism between gallic acid-PPO was also determined. It was concluded that specific concentration of gallic acid can be used to inhibit PPO in production of goods, instead of using protective additives. </p><p>Key Word:Polyphenol oxidase, Kinetics, Gallic acid, Substrate, Inhibitor&nbsp;<br></p>