Heat transfer analysis during hydrothermal treatment of mango.

To export Mexican mango fruit, it is required to comply with phytosanitary regulations, which implies heat transfer. Foods are biological systems with a dynamic behavior and, when they are thermally processed, their thermophysical properties change with temperature. Suitable simulation of heat transfer with temperature-dependent thermophysical properties can provide proper estimations of temperature histories to perform heat penetration analyses. The objective of this study was to predict temperatures within mango and immersion times by varying the mass of the fruit and water temperature during hydrothermal treatments. Thermal conductivity, specific heat capacity, and apparent density of ''Kent'' mango peel and pulp were determined. Finite element analysis was used to simulate heat transfer within the mango. Thermal conductivity and density were different for peel and pulp, but thermal diffusivity for both materials was not different. Predicted temperature histories adjusted properly to experimental data throughout the heating process. This indicates that thermophysical properties as a function of temperature for mango peel and pulp, the convective coefficient, the finite element model, and the methodology used to perform the estimations can be useful in the design of hydrothermal treatments for mango. PRACTICAL APPLICATION: Proper simulation of heat transfer with temperature-dependent thermophysical properties during hot water treatments for mango can provide accurate temperature histories and profiles that allow the prediction of temperatures within the fruit or immersion times by varying the mass and temperature of the heating medium. This will allow a subsequent heat penetration study to predict larval mortality, facilitating the design of quarantine treatments.

Modeling of Effective Moisture Diffusivity in Corn Tortilla Baking.

The objective of this work was to model the mass transfer in corn tortilla baking using different approaches for effective diffusivity based on the Fick's law of diffusion and to evaluate the impact of the process on quality parameters. The 1st one assumes constant effective diffusivity (method of slopes by subperiods and method of successive approximations) and the 2nd one considers variable effective diffusivity (quadratic function of time and Weibull distribution). In addition, the Weibull distribution was applied to fracturability. The effective moisture diffusivity inside the tortilla during baking is not constant and the estimations generated when considering variable diffusivity with quadratic time and Weibull distribution showed better fits (both, R2 = 0.999) to the average moisture content. Quality parameter fracturability was affected by the baking process and the Weibull model adequately described (R2 = 0.996) the fracturability behavior. This work will allow an adequate estimation of the concentration profiles and histories for mass transfer operations in products that can be represented as an infinite plate. The obtained analytical solutions with variable diffusivity will help to estimate the optimal conditions of the baking process to achieve the required final moisture content for baked corn tortilla shells. PRACTICAL APPLICATION: The analytical solutions of the Fick's law of diffusion for the moisture content in products that can be represented as an infinite plate, considering variable diffusivity, can be useful in studies when accurate estimations of effective diffusivity and concentration are needed.

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.