High pressure processing, thermal processing and freezing of 'Camarosa' strawberry for the inactivation of polyphenoloxidase and control of browning

Polyphenoloxidase (PPO) is an enzyme present in strawberry (Fragaria ananassa) which causes undesirable fruit browning, especially if the fruit is cut in pieces or processed into puree. High Pressure Processing (HPP) is an emerging non-thermal food preservation technology with minimum impact on the food original sensory, functional and nutritional properties. As an alternative to conventional freezing/frozen storage of strawberry, the inactivation of PPO in 'Camarosa' strawberry puree by HPP (200 MPa and 600 MPa), thermal processing (29-71 °C) and their combination was attempted for 5 and 15 min processing times. The effect of conventional thermal processing and freezing/frozen storage (−18 °C and −70 °C) for 1 month on PPO was also investigated in puree and whole fruit. Room temperature processing at 600 MPa for 5 min and 15 min resulted in 35% and 82% PPO inactivation, respectively. A 5 min process of 600 MPa in combination with mild heat (40-60 °C) resulted in 9-65% residual activity as opposed to 44-100% with exclusively thermal processing. 200 MPa had minor effect on PPO. Thermal preservation of puree than whole fruit is preferable, whereas frozen storage of whole fruit than puree is better for avoiding strawberry browning. 'Camarosa' strawberry PPO is less resistant to pressure inactivation and more appropriate for HPP technology than 'Elsanta', 'Aroma' and 'Festival' strawberry cultivars.