Optimization of thermal processes relies on adequate degradation kinetic models to warrant food safety and quality. The knowledge on thermal inactivation of enzymes is necessary to allow their proper utilization in food industry and technology applications, enabling the reduction of heating times and optimization of heating temperatures. In this work, the kinetic of thermal inactivation was studied for the previously characterized carboxylmethylcellulases Ab-CX1 and Ab-CX2 from Macrotermes subhyalinus little soldier. Samples of carboxymethylcellulases were treated at different time-temperature combinations in the range of 5-60 min at 50-65°C and the kinetic and thermodynamic parameters for carboxymethylcellulases were calculated. Results showed that inactivation followed a first-order reaction with k-values between 0.0103 ± 0.0003 to 0.1217 ± 0.0005 and 0.0149 ± 0.0007 to 0.0416 ± 0.0003 min -1 for Ab-CX1 and Ab-CX2, respectively. At high temperatures, Ab-CX2 was less resistant, with a significant decrease in residual activity compared to Ab-CX1. The D-and k-values decreased and increased, respectively, with increasing temperature, indicating faster inactivation of carboxymethylcellulases. Activation energy (Ea) and Z-values were estimated to 76.74 ± 1.98 kJ.mol were also calculated. The high value obtained for the variation in enthalpy of activation indicates that a high amount of energy is required to initiate denaturation, probably due to the molecular conformation of carboxymethylcellulases. All results suggest that both carboxymethylcellulases are relatively resistant to long heat treatments up to 50°C.

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Le brunissement enzymatique est associé à l'action des polyphénol oxydases (PPO) et des peroxydases (POD). Les produits de ces enzymes provoquent des changements indésirables de couleur et de saveur des aubergines transformées. Une dopamine oxydase responsable du brunissement enzymatique a été isolée de l’aubergine violette (Solanum melongena L.). Ainsi, l’inactivation thermique et l’analyse thermodynamique ont été étudiées sur une base cinétique afin de contrôler ce phénomène physiologique. Les études cinétiques ont montré que l’inactivation thermique de l’activité dopamine oxydase de l’aubergine violette suivait une cinétique de premier ordre aux températures comprises entre 35 – 80 °C, avec des constantes de vitesse (k) comprise entre 0,0101 ± 0,0001 et 0,0865 ± 0,0004 min-1. Les temps de réduction décimale (D) et k ont diminué et augmenté respectivement avec l’augmentation de la température, indiquant une inactivation plus rapide de la dopamine oxydase à des températures plus élevées. Les résultats suggèrent que dopamine oxydase est une enzyme relativement thermostable avec une constante de résistance (Z) de 50.25 ± 0,7 °C et une énergie d'activation (Ea) de 40.65 ± 0,6 kJmol-1. Les résultats thermodynamiques ont indiqué que les réactions d'oxydation étaient : non spontanées (ΔG > 0), légèrement endothermiques (ΔH > 0) et réversibles (ΔS < 0). Ces données cinétiques peuvent être utilisées dans la prévention du brunissement enzymatique de la pulpe d’aubergine violette par l'inactivation thermique de l'enzyme. Enzymatic browning is associated with the action of polyphenol oxidases (PPO) and peroxidases (POD). The products of these enzymes cause undesirable changes of color and flavor of processed eggplant products. A dopamine oxidase responsible for enzymatic browning was isolated from violet eggplant (Solanum melongena L.). Thus, thermal inactivation and thermodynamic analysis were studied on a kinetic basis to control this physiological phenomenon. Kinetic studies showed that thermal inactivation of dopamine oxidase activity in purple eggplant followed first-order kinetics at temperatures between 35 - 80 °C, with speed constants (k) values between 0.0101 ± 0.0001 and 0.0865± 0.0004 min-1. The decimal reduction times (D) and k values decreased and increased, respectively, with increasing temperature, indicating more rapid inactivation of dopamine oxidase at higher temperatures. The results suggest that dopamine oxidase is a relatively thermostable enzyme with a resistance constant (Z) value of 50.25 ± 0.7 °C and an activation energy (Ea) of 40.65 ± 0.6 kJmol-1. Thermodynamic results indicated that the oxidation reactions were: non-spontaneous (ΔG > 0), slightly endothermic (ΔH > 0), and reversible (ΔS < 0). These kinetic data can be used in the prevention of enzymatic browning of purple eggplant pulp by thermal inactivation of the enzyme.