Effect of high-pressure carbon dioxide on the aggregation and conformational changes of polyphenol oxidase from apple (Malus domestica) juice

This study investigated the effect of different states of CO2 on the activity and structural modification of purified polyphenol oxidase (PPO) from apple juice. CO2 in critical and supercritical states strongly inhibited the PPO activity up to 64.88% and 3.20%, respectively. Dynamic light scattering analysis showed that the two peaks depolymerised into three peaks in the critical state, demonstrating the dissociation and aggregation of small particles. Circular dichroism analysis revealed that the secondary structure deformed because of the loss of α-helix contents in the critical and super critical CO2 states. Fluorescence intensity dramatically decreased to 251.3 (λmax 312) in the critical state, showing unfolding of PPO molecules thereby resulting in quenching and blue shifting of λmax. Electrophoresis indicated that large molecular aggregates did not run into the gel at supercritical state. Hence, HP-CO2 treatment in critical and super critical states could induce the aggregation, deformation and structural changes which might be the causes of PPO inactivation.