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.

The Effects of a Modified Hot Water Treatment on Anastrepha ludens (Diptera: Tephritidae)-Infested Mango.

The Mexican fruit fly, Anastrepha ludens (Loew), is a quarantine pest in mango (Mangifera indica L.) that can be controlled by using a hot water treatment (HWT). This treatment is normally followed by a 30-min hydrocooling (HYC) process that reduces the negative effects that the treatment has on fruit quality. However, if hot water-treated fruits are immediately immersed in water at 21 °C, the survival rate of third-instar A. ludens may be increased. The current approved treatment protocol states that if HYC is used, then treated fruit should undergo an additional 10-min HWT or on platform for 30 min before HYC. We aimed to determine the efficacy of HWT without an additional 10-min treatment before being subjected to HYC, while taking into consideration that the most important conditions are the temperature of the fruit core throughout treatment and the type of infestation, either oviposition or inoculation. Two experimental tests were conducted. Our first aim was to determine the effectiveness of HWT followed by HYC using three varieties and different size classes of mangoes ('Ataulfo' 200-375 and 401-570 g; 'Tommy Atkins' 401-500 and 501-700 g; 'Kent' 401-500 g). The four treatment combinations used to test HWT and immediate HYC at 21 °C were 1) HWT, 2) HWT/HYC, 3) HWT + 10 min/HYC, and 4) HWT/30 min on platform/HYC; an independent experiment was used for each variety. The second aim was to validate the HWT/HYC combination by performing confirmatory tests in commercial packing houses. The results showed that as long as the mango core temperature reached 45 °C during the HWT, it was not necessary to add the 10-min treatment to the HWT before HYC at 21 °C was applied. To ensure that the larvae are subjected to the HWT treatment for sufficient time to be lethal, the temperature of the fruit core throughout the treatment must be recorded.

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.

Third generation snacks manufactured from orange by-products: physicochemical and nutritional characterization.

A mixture of orange vesicle flour, commercial nixtamalized corn flour and potato starch was extruded using a Brabender Laboratory single screw extruder (2:1 L/D). The resulting pellets were expanded by microwaves. Expansion index, bulk density, penetration force, carotenoid content, and dietary fiber were measured for this third-generation snack and optimum production conditions were estimated. Response surface methodology was applied using a central composite rotatable experimental design to evaluate the effect of moisture content and extrusion temperature. Temperature mainly affected the expansion index, bulk density and penetration force, while carotenoids content was affected by moisture content. Surface overlap was used to identify optimum processing conditions: temperature: 128-130 °C; moisture content: 22-24 %. Insoluble dietary fiber decreased and soluble dietary fiber increased after extrusion.

Histopathological changes in third-instar and adult Anastrepha ludens (Diptera: Tephritidae) after in vitro heat treatment.

The Mexican fruit fly, Anastrepha ludens Loew (Diptera: Tephritidae), is one of the most harmful pests of mango causing direct damage by oviposition on the fruit pulp. Mango for export is subjected to hydrothermal treatment as a quarantine method for the control of this pest, but exposure to heat for long periods of time reduces considerably the quality and shelf-life of treated fruit. The aim of this work was to study morphological changes of third-instar larvae and adults of A. ludens after in vitro exposure to high temperature at sublethal times. A heating block system was used to expose larvae at 46.1°C for 19.6 and 12.9 min, producing 94.6 and 70% mortality, respectively. Treated larvae were processed for optical microscopy. A fraction of surviving treated larvae was separated into containers with artificial diet to allow development into adults. Adult sexual organs were dissected and processed for transmission electron microscopy analysis. Results showed that 94.6% of the treated larvae died at 46.1°C for 19.6 min and none of the surviving larvae eclosed to adulthood, as they developed as malformed puparia. For the in vitro treatment at 46.1°C during 12.9 min, 70% of the treated larvae died and only 3.75% reached the adult stage, but ultrastructural damage in the male testes and in the female ovaries was observed. Additionally, 11.1% of the adult flies from the in vitro treatment also showed wing malformation and were incapable of flying. The analysis showed that surviving flies were unable to reproduce.

Hot-water phytosanitary treatment against Ceratitis capitata (Diptera: Tephritidae) in 'Ataulfo' mangoes.

We determined the thermal death rate constants and mortality curves for the eggs and different instars of Ceratitis capitata (Mediterranean fruit fly) (Wiedemann) submerged in isolation in water at 44, 46, and 48 degrees C and submerged within fruits of Mangifera indica (mango) (L.) in water at 43.1, 44.1, 45.1, and 46.1 degrees C. The first instar was the most tolerant to this treatment, with estimated times for achieving 99.9968% mortality of 103.28, 92.73, and 92.49 min at temperatures of 43.1, 44.1, and 45.1 degrees C, respectively. The results of the study indicate that 'Ataulfo' mangoes weighing < 329 +/- 2.11 g and at risk immature Mediterranean fruit fly infestation should be immersed for 95 min at 46.1-47 degrees C to ensure that the fruit pulp remains at this temperature for 10 min. An efficacy test was conducted that involved treating 730 mangoes, with an average weight of 326 +/- 2.11 g (mean +/- SE) and infested with 84 +/- 1.15 first instars. In this test, none of the 61,720 larvae treated survived. The confirmatory test was performed using commercial equipment in which 1,112 infested mango fruit weighing an average of 329 +/- 2.11 g were treated. Each fruit was previously infested with an average of 59 +/- 0.61 first instars (= 65,825 total larvae) of which none survived. The data collected on mango quality indicate that hot water immersion for 95 min at 46.1-47 degrees C can produce a more uniform fruit-color and positively modify the pH (producing more palatable fruits), but can also produce a loss of firmness and weight (5%). Taking all factors into consideration, we conclude that this treatment is sufficient to meet quarantine restrictions against C. capitata while maintaining market quality at least for 15 d.