Kinetics of peroxidase inactivation, color and temperature changes during pumpkin (Cucurbita moschata) blanching using infrared heating

Fresh Pumpkin is sensitive to microbial or enzymatic spoilage even in refrigeration temperatures, thus; blanching before freezing or canning is a proper way for preservation and commercialization of this product. In this study infrared irradiation was chosen as heating source and peroxidase as an indicator of enzyme inactivation adequacy for pumpkin blanching. Pumpkin purée was treated under 5 levels of temperature and 2 levels of sample thickness. Effect of thermal processing on the kinetic parameters of peroxidase inactivation (k, Ea, D and Z values) and color changes (ΔE) was investigated. Peroxidase inactivation of pumpkin samples followed a first order kinetics model. Calculated activation energies and Z values of enzyme inactivation process for 4 and 8 mm thickness levels were 130.63, 119.46 kJ mol−1 and 18.18, 17.85 °C, respectively. No significant difference was observed between activation energies and Z values of two thickness levels. But, the effect of temperature and thickness on inactivation rate constants (k) and D values was significant (P < 0.05). Investigation on the kinetics of color change was carried out by the calculation of ΔE changes during l log enzyme inactivation period. In this study, sample thickness showed a more significant effect on ΔE variations than temperature.