## 4 Kinetic Modelling of PPO Inactivation
### High Pressure Inactivation Kinetics of PPO  
The inactivation kinetics of PPO of different fruits processed at 400-600 MPa typically followed first-order behaviour [57; 58; 59]. PPO inactivation in lychee, sapodilla, and PPO in pear showed first-order inactivation kinetics [57; 58; 59]. However, in terms of kinetic inactivation by HPP in apple cv. Royal Gala puree and strawberry cv. Camarosa puree, [PERSON] [9] reported that these data showed non-linear first-order kinetics, better fitted with biphasic models. The difference in models could be due to the presence of isoenzymes with similar structures but different resistance to pressure and temperature that could explain the biphasic behaviour [62]. High pressure inactivation kinetic parameters for different fruits and cultivars are summarised in Table 3. The differences in E\({}_{a}\) could be attributed to the enzyme extract being processed in a buffer rather than the fruit itself because the medium in which PPO is suspended can change its resistance, as [PERSON] [63] previously reported.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fruit/Cultivar** & **Temperature (°C)** & **k (min\({}^{-1}\))** & **D-Value (min)** & **z-Value (°C)** & **E\({}_{a}\), (kJ/mol)** & **Reference** \\ \hline Kalipatti sapota & & & & & & \\ (_Manilkara zapota_) & 75 & 0.288 & 8 & 15.2 \({}^{\circ}\)C & 158 & [36] \\ pulp & & & & & & \\ \hline Bayberry (_Myrica_) & 65 & 0.0888 & 26 & 13.2 \({}^{\circ}\)C & 152 & [39] \\ juice & 75 & 0.370 & 6 & 13.2 \({}^{\circ}\)C & 152 & [39] \\ \hline Pear & & & & & & \\ (_Pyrus communis_ cv. & 75 & 0.019 & 121 & 6.0 \({}^{\circ}\)C & 375 & [28] \\ Taylor’s Gold) & 80 & 0.214 & 11 & & & \\ puree & & & & & & \\ \hline Apple (_Malus domestic_ & & & & & \\ cv. Royal Gala) & 75 & 0.103 & 22 & 17.0 \({}^{\circ}\)C & 134 & [28] \\ puree & & & & & & \\ \hline Strawberries & & & & & & \\ (_Fragaria ananasa_ cv. & & & & & \\ Camarosa) & 60 & 0.144 & 16 & 14.0 \({}^{\circ}\)C & 147 & [28] \\ Puree & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Thermal inactivation kinetic parameters.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & & & & & & \\ \hline
**Fruit/Cultivar** & **Parameters** & **k\({}_{a}\)** & **E\({}_{a}\)(k)** & **E\({}_{a}\)(k)**, & **E\({}_{a}\)(k)**, & **D\({}_{g}\)-Value** & **z\({}_{g}\)-Value** & **z\({}_{g}\)-Value** & **D\({}_{l}\)-Value** & **z\({}_{l}\)-Value** & **z\({}_{l}\)-Value** \\
**Fruit/Cultivar** & **Parameters** & **k\({}_{a}\)** & **(min\({}^{-1}\))** & **(dj/mol)** & **(min\({}^{-1}\))** & **(dj/mol)** & **(min)** & **(°C)** & **Reference** \\ \hline Apple & 600 MPa & & & & & & & \\ (_Malus domestic_ cv. & 57 \({}^{\circ}\)C & 0.0121 & & 0.0266 & & 190 & 86 & & \\ Royal Gala) & 600 MPa & & & & & & & \\ puree & 71 \({}^{\circ}\)C & 0.0184 & & 0.0613 & & 124 & & 38 & \\ \hline Strawberry & 60 MPa & & & & & & & \\ (_Fragaria ananasa_ cv. & 57 \({}^{\circ}\)C & 0.0182 & & 0.213 & & 127 & & 11 & \\ Camarosa) & 60 MPa & & & & & & & \\ puree & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Kinetic parameters of inactivation PPO by HPP. PPO inactivation with biphasic behaviour (a) and first-order inactivation of PPO (b).