The Deglet-Noor Date Polyphenoloxidase Activity Is Very Thermolabile and Exhibits Peculiarities in Its Thermal Inactivation Kinetics

Abstract

In our current research on the preservation of the Deglet-Noor date quality during thermal processing, the heat inactivation of the polyphenoloxidase in enzyme extracts of this fruit was investigated. In contrast to previous studies on this enzyme in this exotic fruit, we performed full kinetic analyses at different temperatures (25–70°C) and enzyme activity was measured by the initial velocity methodology. The heat-inactivation of the polyphenoloxidase from the Deglet-Noor date does not obey a simple “one step-two stages” mechanism. All the recorded kinetics were described using a simple three parameters-biexponential model that we previously showed to be a common arranged form of kinetic expression for the known wide diversity of mechanisms of enzyme deactivation. The values of the two rate constants of the model were collected for four temperatures, ranging from 25 to 70°C and their variation was analyzed through the ARRHENIUS's law to determine the Ea values (11.83 and 54.71 kJ mol⁻¹, respectively). Possible explanations and implications of such low values are discussed. These results are compared to other results from laboratory as well as elsewhere in the literature.

Keywords:

• Enzyme heat inactivation
• Polyphenoloxidase
• Date
• Phoenix dactylifera

Acknowledgments

A. B. was supported by a scholarship and financial support from the Algerian government. The contribution of Miss. Sophie Daguenet to a part of this study is gratefully acknowledged.