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.

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.

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Recently immobilized enzymes have been widely used in industrial processes due to their outstanding advantages, such as high stability and recyclability; however, their kinetic behaviour is generally controlled by mass diffusion effects. Thus, in order to improve these enzymatic processes, a clear discernment between the kinetic and diffusion mechanisms that control the production of the metabolite require investigation. In practice, it is typical to establish apparent kinetics for immobilized enzyme operations, and the validity of the apparent kinetics is restricted to the studied cases. In this work, a new approach for mathematically describing the kinetic and diffusion mechanics in an immobilized biocatalyst bead is established, in which the fraction of residual enzymatic activity is included, and is defined as a measure of the active and available enzymes in the bead porous network. In addition, the diffusion and kinetic mechanisms are described by the effective diffusion coefficient and the free enzyme kinetics, since the porous network of the bead is assumed as the bioreaction volume. Therefore, free enzyme kinetics were determined from glucose to fructose bioconversion using a stirred tank reactor with free glucose‐isomerase, in which substrate and enzyme concentrations and temperature were varied. The fraction of residual enzymatic activity (η=0.553) and the effective diffusion coefficient (Deff=normal8.356×10−12m2/normals) were obtained from the isomerization of glucose to fructose using a stirred tank reactor with immobilized glucose‐isomerase in calcium alginate beads at different substrate and enzyme concentrations. Finally, simulations were carried out to establish the bioreaction solid‐phase characteristics that most significantly influence productivity.

Modified atmosphere packaging and refrigeration of fruits and vegetables are used to extend their shelf life. The objective of this research was to evaluate quality variables in avocado (Persea americana Mill.) cv. "Hass" during storage in modified atmosphere packaging (MAP) at 8 °C and contrast them to those obtained during storage at room temperature (RT) and refrigeration (REF). Fruits at physiological maturity were stored in MAP bags with a thickness of 0.20 mm. A completely randomized design was used; factors were: type of storage (RT 21 °C, REF 8 °C, and MAP 8 °C), storage time (8, 16, 24, and 32 days), and ripening time after storage (2, 4, and 6 days). Quality variables were firmness (penetration force), total color difference (ΔE) in exocarp and mesocarp (colorimeter), pH (potentiometry), and total soluble solids (TSS, refractometry). Avocados stored in MAP maintained (p > 0.05) firmness, which was higher compared to REF and RT during the storage period. Firmness retention for avocados at RT, REF, and MAP, at day 16, was 5.7, 32.6, and 87.2%, and at day 32, it was 0 (no reading), 9.5, and 78.2%, respectively. Total color difference in exocarp and mesocarp, pH, and TSS ranged from 3.8 to 25.6, 3.2 to 20.3, 6.7 to 7.1, and 5.3 to 7.7 °Brix, respectively. During the storage period, fruits stored at MAP showed a firmness, ΔEexocarp, and ΔEmesocarp similar to those of fresh fruit. Type of storage showed no effect on pH and TSS during the storage period. The package for modified atmosphere at 8 °C allows to prolong the shelf life of “Hass” avocado for a period twice as long as that at room temperature, based on the fact that changes in firmness and color are reduced, properties that are important quality benchmarks.