Kinetic and Thermodynamic Characterization of Latent and Activated Polyphenol Oxidase from Zrèzrou Yam (Dioscorea cayenensis rotundata) Cultivated in Ivory Coast for the Control of Enzymatic Browning

Abstract

In the Zrèzrou yam (Dioscorea cayenensis rotundata), cultivated in Côte d’Ivoire, polyphenol oxidase (PPO), the enzyme responsible for enzymatic browning, exists in latent and activated forms, whose properties were poorly documented. This study aims to conduct a detailed comparison of the kinetic and thermodynamic parameters of these two enzymatic forms. PPO extracted from fresh tubers was purified, and its activated form was obtained by adding 0.4% sodium dodecyl sulfate (SDS) to the reaction medium. Kinetic parameters (Vmax, Km, catalytic efficiency) were determined by spectrophotometry, while thermodynamic parameters (activation energy Ea, enthalpy ΔH#, entropy ΔS#, Gibbs free energy ΔG#) were calculated from activity data as a function of temperature. The results revealed no significant difference between the two forms in terms of Km values. However, the latent form has a higher Vmax and catalytic efficiency than the activated form, indicating enhanced substrate affinity. Thermodynamically, the latent form shows a lower Ea (78.92 KJ) than the activated form (129.92 KJ), suggesting that the catalyzed reaction requires less energy and that the latent form has better thermal stability. The average positive ΔH# (76.27 KJ) and negative ΔS# (-36.41 KJ) values confirm the endothermic nature of the reaction and the formation of an ordered enzyme-substrate complex for the latent form, while the positive ΔG# values for both forms indicate the non-spontaneity of the process. These results provide a scientific basis for the development of effective strategies to control enzymatic browning, in order to improve the food and industrial valorization of this tuber in Côte d’Ivoire.