Luis Andrés Segura

In this study, we aimed to describe a modern, efficient, and reproducible methodology to optimize respiration rate parameters coupled with transport properties in mass balances describing Modified atmosphere packaging (MAP) systems. We considered mass balances for three different respiration rate j film (exponential, competitive and uncompetitive Michaelis–Menten kinetics) coupled with transport properties for two different packaging films. Experiments were conducted to validate the methodology using grapes placed in a polypropylene container opened on the top and sealed with packaging films. The methodology relies on a numerical optimization procedure called the Trust-Region-Reflective algorithm. We determined the predictive capability of models using goodness-of-fit criteria and assessed parameter uncertainty through standard errors. We also calculated the first-order optimality measure and the relative change in the sum of squares to verify the convergence of the implemented algorithm. Results showed that the respiration rate parameters obtained with this methodology for the exponential model provided a better fit than for the other two models. The fitting for the kinetic models is not very suitable since we found that the normalized standard errors were rather high. In conclusion, the methodology is robust, and we expect that it serves as a tool for assessing MAP technology design.

In some important berry-producing countries, such as Chile, the fruit is harvested manually. The markets for these products are generally very distant, and any damage caused to the fruit during harvesting will be expressed in its shelf life. The first step to understanding the harvesting process is to identify what happens to the harvest baskets in each stage (picking, wait-full, transport-full, freezing tunnel, emptying and transport-empty), allowing variables that can affect the shelf life to be identified. This article proposes the use of Smartbins, intelligent harvest baskets with sensors to collect weight, temperature, and vibration data. Combined analysis of the variables collected, using machine learning algorithms, allows the system to estimate which stage the basket is at with an accuracy of 80%, and to assess whether the fruit has been exposed to situations that could affect its shelf life. Due to imbalance characteristics of the data collected, the best results were obtained in longer stages (picking and wait-full stages with 89% and 86% respectively).

- Basically, micromodels are devices simulating a porous network and are useful tools for studying the transport mechanisms that govern the drying proce...

The relationship between water content and capillary pressure and the microstructural changes in apples (Granny Smith) during drying was studied. Apples were dried in a pilot tray dryer and samples, with different moisture contents, were put in liquid nitrogen. The remaining water was eliminated by the critical point method to avoid structural changes and samples were then observed by scanning electron microscopy (SEM). It was possible to characterize the internal space of the apples during drying and find a relationship between the drying rate and microstructural changes. We postulate that shrinkage during drying is mainly due to changes in capillary pressure.

Microscopic visualization, especially in transparent micromodels, can provide valuable information to understand the transport phenomena at pore scale in different process occurring in porous materials (food, timber, soils, etc.). Micromodels studies focus mainly on the observation of multi-phase flow, which presents a greater proximity to reality. The aim of this study was to study the process of flexography and its application in the manufacture of polyester resin transparent micromodels and its application to carrots. Materials used to implement a flexo station for micromodels construction were thermoregulated water bath, exposure chamber to UV light, photosensitive substance (photopolymer), RTV silicone polyester resin, and glass plates. In this paper, data on size distribution of a particular kind of carrot we used, and a transparent micromodel with square cross-section as well as a Log-normal pore size distribution with pore radii ranging from 10 to 110 µm (average of 22 µm and micromodel size of 10 × 10 cm) were built. Finally, it stresses that it has successfully implemented the protocol processing 2D polyester resin transparent micromodels. Visualização microscópica, especialmente em micromodelos transparente, pode fornecer informações valiosas para a compreensão dos fenômenos de transporte de poros em diferentes processos que ocorrem em materiais porosos (alimentos, madeira, solos, etc.). Micromodelos estudos centram-se principalmente na observação de fluxo multifásico, que apresenta uma maior proximidade com a realidade. O objetivo deste trabalho foi estudar o processo de flexografia e sua aplicação na fabricação de resina de poliéster micromodelos transparente e sua aplicação para as cenouras. Os materiais utilizados para implementar uma estação de flexo para fazer micromodelos fosse um banho termostatizado, câmara de exposição à luz ultravioleta, a substância fotossensível (fotopolímero), resina de poliéster, silicone RTV e placas de vidro. No presente trabalho foram utilizados dados sobre a distribuição do tamanho de um tipo particular de cenoura e foi construído um micromodelo transparente, com secção transversal quadrada, tamanho e distribuição log-normal de poros com raios de poros que variam de 10-110 µm (media de 22 µm e micromodelo tamanho de 10 × 10 cm). Por fim, salienta que implementou com sucesso o processamento do protocolo 2D micromodelos resina de poliéster transparente

This work presents results of Monte Carlo simulations of isothermal drying of a nonhygroscopic porous media initially saturated with a sugar solution. The porous media is represented by a two-dimensional network of cubic pores connected by throats with a given radius distribution. The considered network had just one open side (the three other sides were sealed) from which water evaporation occurred. Water evaporation, hydraulic flow, and diffusivity of sucrose in water are considered in the physical model. It was considered that drying occurred under isothermal conditions (low drying rates) and that the capillary forces surpass the viscous forces, as in invasion percolation. It was also considered that water evaporation inside the network of pores and throats causes solution concentration, which remains at the corners, allowing hydraulic connection throughout the whole network. At each simulation step, a single meniscus moves through a particular pore segment with the higher displacing force. As drying progresses, air replaces the solution. Determination of the mechanism prevailing at any given drying stage requires calculation of evaporation. In other words, each step of the simulation involves finding the solution to three systems of equations: the vapor pressure field in the vapor phase, the pressure field in the liquid phase, and the solutes' concentration in the liquid phase. Herein, we report results of drying curves calculated as a function of the sucrose and water saturation and of the distribution of liquid, sucrose, and vapor as drying advances. The results presented in this work showed that network models are a powerful tool for investigating the influence of the main mechanisms controlling drying at its different stages; that is, from liquid saturation condition to very low saturation (end of drying). Despite the applied simplifications, the model can capture the main aspects of drying of liquids and solutions present in porous media.

Formulating wood drying models with predictive capabilities is still a challenge. Traditionally, the wood drying process is studied macroscopically, with pore-level physics lumped into effective transport properties. However, microvisual experiments in 2-D transparent porous media (known as micromodels) can improve our understanding of the drying process and add to current theories. Here, we make etched glass micromodels with the pore morphology of softwoods and carry out simple drying experiments, thereby proving the potential of this experimental tool on the wood science field. We develop a procedure to generate the random morphology of softwood with a computer program based on known probability distribution laws. In particular, we generate the tracheid cell microfeatures of a softwood longitudinal-tangential section. The wood morphology is etched onto glass using a photolithographic technique, creating softwood glass micromodels. Good agreement is seen between the morphology of microtome sections and our computer-generated softwood. During wood drying, liquid flow is driven by capillary instabilities. Sudden liquid redistribution, know as a Haines jump, spontaneously drains the liquid contained in cell cavities. Viscous flow occurs mainly through liquid films in partially dry cells.