Kinetic and thermodynamic characterization of thermal inactivation of polyphenol oxidases and peroxidases in cassava roots (Manihot esculenta Crantz) variety yacé

Abstract

This study characterized the thermal inactivation of polyphenol oxidases (PPO) and peroxidases (POD) in three tissues (inner bark, cambium, central cylinder) of cassava roots (Manihot esculenta Crantz) variety Yacé to prevent post-harvest enzymatic browning. Crude enzymes were extracted and subjected to thermal treatments from 35°C to 70°C. Kinetic parameters (half-life t1/2, D-value, Z-value) and thermodynamic parameters (activation energy Ea, enthalpy ?H, entropy ?S, free energy ?G) were determined. PPO exhibited optimal pH values of 8.6 to 9.6 and optimal temperatures of 30 to 45°C, while POD were optimal at pH 6.6-8 and 35-45°C. Specific activities ranged from 6.44 to 18.31 U mg?¹ for PPO and 7.66 to 9.54 U mg?¹ for POD, with higher values in the cambium. At 70°C, t1/2 ranged from 2.19 to 3.74 min for PPO and 2.98 to 3.21 min for POD, with D-values of 7.28 to 12.76 min. Z-values ranged from 17.03 to 37.45°C, and Ea from 54.33 to 122.89 kJ/mol. Reactions were endothermic (?H: 51.48-120.25 kJ/mol), non-spontaneous (?G > 0), and involved molecular compaction (?S: -99.77 to -10.10 J mol?¹ K?¹). These findings suggest that thermal treatments at 60-70°C for 10-15 min can effectively inactivate PPO and POD, reducing browning and extending cassava shelf life.