The quality and freshness of fruit juices can be related to the colour, turbidity and cloud stability. Changes in these attributes are mostly due to reactions catalysed by enzymes, such as PPO and PME, so that is desirable to inactivate them during the treatment before commercialisation. PPO is the key enzyme in enzymatic browning of fruits and vegetables, producing changes in appearance of the juice. The principal colour change is due to polymerization of ortho-quinones, produced during catechol enzymatic oxidation. The antioxidants concentration such as ascorbic acid and polyphenols belonging to juice can prevent and reverse this oxidation. developed a polynomial model to describe the rate of PPO inactivation in cloudy apple juice as a function of pressure and temperature, showing synergistic effects of these variables on the inactivation of PPO at pressures above 300 MPa, and antagonistic effects at lower pressures. Turbidity in juices is attributed to soluble pectin, so it is necessary to inactivate the PME wall-bounded whose substrate its pectin. PME de-esterifies pectin producing methanol and lowmethoxil pectin, which precipitates in presence of calcium ions resulting in clouding control. Reported work on inactivating PME on clear apple juice (200e400 MPa, 0e180 min). The effects of pressure level and pressure holding time on enzyme inactivation were significant.