Thermal Inactivation Kinetics of Peroxidase and Polyphenol Oxidase in Long Bean (Vigna sesquipedalis) and the Changes in their Activities during Storage

The thermal inactivation kinetics by hot water blanching of peroxidase and polyphenol oxidase in long beans (Vigna sesquipedalis) was investigated. Kinetic parameters such as the inactivation rate constant, activation energy and decimal reduction time were also determined. Peroxidase exhibited a biphasic inactivation behavior at 45-85 degrees C with activation energies of 35.07 and 89.86 kJ/mol, respectively. However, polyphenol oxidase was monophasic at all temperatures with an activation energy of 98.25 kJ/mol. After 6 months of storage at -18, 0 and 5 degrees C, the peroxidase activities of unblanched samples with respect to the level before storage were 42.20, 34.96 and 29.13 %, respectively, whereas the polyphenol activities were 68.44, 65.38 and 60.36 %, respectively. For blanched samples, the changes in peroxidase and polyphenol oxidase activities were approximately zero for storage at -18 degrees C, whereas at the other temperatures, it experienced an increase of less than 4 %. Overall, this research gives insights into the long time storage of long beans. The blanching of long beans at 95 degrees C for 12 min inactivates both these enzymes, and thus may increase the storage life of long beans.