PME was completely inactivated by the HPP treatment and the enzyme did not recover any activity during the monitored shelf life period of 34 days. High pressure and time effects over the PPO activity are shown in Fig. 1. Short time treatments at any pressure tested increased the PPO activity up to 1.6 times, which was significant (p < 0.05) compared with the native enzyme activity. At As previously mentioned, enzyme inactivation in fruit juices does not follow a predictable trend. For example reported a 0.12 log cycles PPO activity reduction in apple juice with one pulse of 400 MPa while reported a 3-fold PPO activation increase of grape juice treated at 400 MPa and 550 MPa respectively. These contradictory results in activity changes may be due to different denaturing pathways of the enzyme. Secondary structure is mainly stabilised by hydrogen bonds and tertiary structure is maintained by hydrophobic and ionic interactions, which are disrupted at high pressures. Hence, the activity achieved after HPP treatment may be due to active site modification, which can be exposed increasing their activity or can be enclosed or denatured resulting in a decrease of the activity. In this study, PPO was partially denatured and completely inactivated during HPP treatments, but after 13 days an increase in its activity was noted in both storage temperatures The enzyme recovered 20% of its capacity to oxidise catechol, but not significant changes (p > 0.05) in total polyphenols were observed during the storage time. The PPO active site was partially recovered after two weeks, but was unable to react with the polyphenols, probably due to its tertiary structure modification.