Kinetic and Thermodynamic of Thermal Inactivation of the Peroxidase, Polyphenoloxidase and Inulinase Activities during Blanching of Yacon (Smallanthus sonchifolius) Juice

Abstract

The present study evaluated the kinetics and thermodynamic parameters for the thermal inactivation of peroxidase (POD), polyphenoloxidase (PPO) and inulinase (INU) from yacon juice. The yacon juice was acidified with 1 % citric acid prior to blanching at different time-temperature combinations in the range of 0–10 min, and 80–100 °C. All enzymes showed a biphasic kinetic behavior. The velocity constants increased and D values decreased with temperature for both the labile and the heat resistant fractions. The activation energy of the heat-labile (E aL ) and heat-resistant fractions (E aR ) were 38.19, 16.05, 30.08 kJ/mol, and 30.65, 71.94, 41.86 kJ/mol for POD, PPO and INU, respectively. Thermodynamic studies indicated a non-spontaneous (ΔG > 0) and endothermic (positive enthalpy values) process, and the enzyme aggregation step is the rate determining of the reaction (negative entropy values).