Rheological characteristics and thermal degradation kinetics of beta-carotene in pumpkin puree

The degradation kinetics of both the beta-carotene and visual color of pumpkin puree (blanched for 2 min in 1% NaCl solution) were determined at a temperature range of 60-100 degrees C for a time period varying between 0 and 2 h. An increase in the beta-carotene content was observed when the pumpkin puree was blanched and thermally treated at 60 degrees C. Using the concept of fractional conversion, it was observed that the degradation of both beta-carotene and visual color followed the first-order reaction kinetics. Dependence of the rate constants followed the Arrhenius relationship. The activation energy for beta-carotene was found to be 27.2715 kJ/mol and the activation energy for visual color using La/b and Delta E values was found to be 33.6831 kJ/mol and 30.3943 kJ/mol respectively. Higher activation energy signifies greater temperature sensitivity of visual color. The change in visual color was found to be a direct manifestation of the change in beta-carotene content. Rheological characteristics of the puree was also studied over the temperature range of 60-100 degrees C. Herschel-Bulkley model was found to fit adequately over the entire temperature range. Pumpkin puree exhibited yield stress, which decreased exponentially with temperature. With the increase in temperature, the puree was found to behave as a pseudoplastic fluid. Arrhenius model gave a satisfactory description of the temperature dependence of apparent viscosity. The activation energy for apparent viscosity and consistency index of pumpkin puree was found to be 13.3845 kJ/mol and 31.9394 kJ/mol respectively. (c) 2005 Elsevier Ltd. All rights reserved.