High pressure and thermal inactivation kinetics of polyphenol oxidase and peroxidase in strawberry puree

Abstract

The objective of this work was to study the thermal and high pressure inactivation kinetics of polyphenol oxidase (PPO) and peroxidase (POD) in strawberry puree. PPO from two strawberry cultivars (‘Festival’ and ‘Aroma’) was found to be highly thermostable in strawberry puree with no significant inactivation even after 30 min treatment at 100 °C. In contrast, POD from the two cultivars displayed very high thermosensitivity with complete inactivation in less than 5 min at 70 °C. The thermal inactivation kinetics of strawberry POD was described by a biphasic model. The activation energies for the inactivation of the stable and the labile fractions were estimated to be 254.9 and 221.6 kJ/mol respectively. Combined high pressure–thermal treatment at pressures ranging from 100 to 690 MPa, temperatures ranging from 24 to 90 °C and treatment times between 5 and 15 min did not have significant effect on PPO while substantial inactivation of POD was observed. The inactivation kinetics of POD during combined high pressure–thermal processing was well described by first-order kinetics probably due to the inactivation of the labile fraction during the pre-heating and the compression phase. The oxidative enzymes polyphenol oxidase and peroxidase cause the degradation of anthocyanins and other polyphenols in strawberry products, leading to discoloration and loss of antioxidant activity. In this work the thermal and high pressure inactivation of strawberry polyphenol oxidase and peroxidase was investigated so as to assess the suitability of high pressure processing as an alternative to thermal processing. Strawberry polyphenol oxidase was found to be highly resistant to both thermal and high pressure inactivation. Thus in order to maintain the quality of processed strawberry products, high pressure processing should be accompanied by additional measures such as exclusion of oxygen, refrigerated storage and the use of natural enzyme inhibitors.