Thermal Inactivation Kinetics of Peroxidase in Selected Nigerian Leafy Vegetables

Peroxidase is a heat-resistant enzyme used as a marker for blanching adequacy in vegetable processing, and its inactivation kinetics are essential for the design of effective pre-treatment protocols. This study determines the thermal inactivation kinetics of peroxidase in three leafy vegetables commonly consumed in Nigeria: Telfairia occidentalis (fluted pumpkin), Amaranthus hybridus (green), and Corchorus olitorius (jute mallow). Samples were collected from markets in Enugu (South East), Lagos (South West), and Abuja (North Central). Crude enzyme extracts were prepared by homogenisation and centrifugation. Thermal inactivation experiments were conducted at temperatures of 60, 70, 80, and 90 degrees Celsius using a water bath, with sampling at one-minute intervals. Enzyme activity was determined spectrophotometrically at 470 nm using guaiacol as the hydrogen donor. Inactivation data were fitted to first-order kinetic models to determine decimal reduction time (D-values) and z-values. Results showed that peroxidase from Corchorus olitorius was most heat-resistant, with a D70 value of 4.2 minutes, while Amaranthus hybridus was least resistant at 1.8 minutes. Z-values ranged from 18 to 26 degrees Celsius. The study contributes to the thermal processing literature for tropical African leafy vegetables and provides kinetic parameters for the design of blanching protocols in vegetable processing operations. Keywords: peroxidase, thermal inactivation, blanching, leafy vegetables, Nigeria