In-vitro assay and inactivation kinetics of polyphenol oxidase of some Nigerian banana and plantain cultivars

Activity of polyphenol oxidase (PPO) from the pulp of three banana cultivars grown in Nigeria, namely: plantain, light green-skinned banana and red-skinned banana at unripe and ripe states were investigated. The efficiency of extraction of crude PPO enzyme and in-vitro assay of its activity were determined. Polyethylene glycol detergent gave the highest extraction efficiency. Enzyme activity and rate of browning were found to be highest in plantain and least in light green-skinned banana. Enzymes from all the cultivars were specific towards O-diphenolic compounds and not to monophenolics. The optima pH of PPO of the cultivars tends towards neutrality (6.6-7.0). Enzyme activity was destroyed between 2 and 4 min at 80°C. Thermal inactivation kinetic parameters revealed plantain's PPO to be the most thermal stable. Sodium metabisulphite was the most effective chemical inhibitor of the PPO. The electrophoretic patterns of banana PPO showed heterogeneity with greater number of bands in ripe.