Thermodynamic Stability and Inhibition Kinetics of Polyphenol Oxidase in African Bush Mango (Irvingia gabonensis): Implications for Postharvest Browning Control

The study sought to investigate the catalytic effect of polyphenol oxidase (PPO) in adverse browning of African bush mango (I. gabonensis) fruit. PPO was isolated, purified and its physicochemical properties and thermodynamic stability were investigated. The pH and temperature optima of PPO were found at 7.0 and 50 °C respectively. However, the enzyme exhibited a higher activity at neutral pH 7.0, given a percentage activation of 90%, while the enzyme inhibition was observed at the acidic region between pH 2.0 - 5.0. The presence of SDS at pH 2.0 - 5.0 was found to inhibit the activity of PPO. The average values of enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) obtained at 20 min of incubation and temperature 30 – 80 °C were respectively 39.93 KJ/mol, 431.57 J/K and -107.99 KJ/mol for peel PPO, and 37.92 KJ/mol, 442.51J/K, and -107.22 KJ/mol for pulp PPO. The information from this study suggests processing parameters for controlling PPO in potential industrial application of I. gabonensis fruit to minimize browning in processed product in order to prolong the shelf-life of the product for maximum utilization.