Numerical model for the combined simulation of heat transfer and enzyme inactivation kinetics in cylindrical vegetables

Optimizing Thermal Processing of Broccoli: Model Development, Numerical Simulation, Experimental Validation

Kinetic models describing the thermal inactivation of peroxidase and degradation of broccoli (Brassica Oleracea var. Italica) color were coupled with heat transfer equation (2D conductive heat transfer in cylindrical packed broccoli samples), and their simultaneous numerical simulation followed by experimental validation was carried out. Obtained results revealed that modeling the rate constants of the reactions with log logistic equation provides a better prediction in comparison with the most popular Arrhenius equation. It was observed that processing at temperatures lower than 80 °C is not recommended for processing of broccoli due to its adverse effect on the color of samples and considerable longer process time needed for assuring sufficient inactivation of enzyme at the cold spot. Temperatures above 80 °C were suitable for this purpose because the process time needed for inactivating peroxidase at the cold spot of sample not only affected the green color of samples negatively, but oppositely it resulted in a higher greenness than the original value.

Heat Transfer during Blanching and Hydrocooling of Broccoli Florets

The objective of this work was to simulate heat transfer during blanching (90 °C) and hydrocooling (5 °C) of broccoli florets (Brassica oleracea L. Italica) and to evaluate the impact of these processes on the physicochemical and nutrimental quality properties. Thermophysical properties (thermal conductivity [line heat source], specific heat capacity [differential scanning calorimetry], and bulk density [volume displacement]) of stem and inflorescence were measured as a function of temperature (5, 10, 20, 40, 60, and 80 °C). The activation energy and the frequency factor (Arrhenius model) of these thermophysical properties were calculated. A 3-dimensional finite element model was developed to predict the temperature history at different points inside the product. Comparison of the theoretical and experimental temperature histories was carried out. Quality parameters (firmness, total color difference, and vitamin C content) and peroxidase activity were measured. The satisfactory validation of the finite element model allows the prediction of temperature histories and profiles under different process conditions, which could lead to an eventual optimization aimed to minimize the nutritional and sensorial losses in broccoli florets.