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Maintaining optimal atmosphere conditions for fruits and vegetables throughout ...
Brech, J. K.; Chau, K. V.; Fonseca, S. C.; Oliveira, F. A. R.; Silva, F. M.; Nunes, M. C. N.; Bender, R. J.Optimal controlled and modified atmospheres (CA and MA) for fresh produce vary according to the specie, its maturity or ripeness stage, the temperature, and the duration of exposure. However, individual lots of produce are typically handled for different times and at different temperatures during storage, transportation, and retail display. In this paper, we review some of our previous work showing the potentia...
A study on the accuracy and precision of external mass transfer and diffusion c...
Azevedo, I.C.A.; Oliveira, F.A.R.; Drumond, M.C.Optimal experimental designs for maximum precision in the estimation of diffusivities (D) and mass transfer coefficients (Kc) for solute transport from/to a solid immersed in a fluid were determined. Diffusion in the solid was considered to take place according to Fick's second law. It was found that the optimal design was dependent on the Biot number. In the range of Biot numbers tested (0.1±200), the first sa...
Application of the acid hydrolysis of sucrose as a temperature indicator in con...
Torres, A. Pinheiro; Oliveira, F. A. R.The hydrolysis of sucrose in an acid medium was used as a temperature indicator to measure holding temperatures in a continuous thermal-processing unit. From a theoretical analysis, target conversion (χ) and errors in both acid concentration and conversion measurements were found to affect significantly the accuracy of predicted temperatures, whereas errors in the determination of the fluid mean residence time ...
Modelling the kinetics of water loss during potato frying with a compartmental ...
Costa, R. M.; Oliveira, F.A.R.The complexity of the frying process impairs the development of mechanistic models to describe water losses. Empirical models, though lacking a theoretical basis, may provide a suitable and simpler alternative. In this work it was found that a two parallel compartments model (core and edge compartments), with a time-dependent boundary condition, could be successfully applied for this purpose. The model showed a...
A study on the accuracy and precision of external mass transfer and diffusion c...
Abreu, Isabel; Oliveira, F. A. R.; Drumond, M. C.Optimal experimental designs for maximum precision in the estimation of diffusivities (D) and mass transfer coefficients (Kc) for solute transport from/to a solid immersed in a fluid were determined. Diffusion in the solid was considered to take place according to Fick's second law. It was found that the optimal design was dependent on the Biot number. In the range of Biot numbers tested (0.1±200), the first sa...
Residence time distribution of liquids in a continuous tubular thermal processi...
Torres, A. Pinheiro; Oliveira, F. A. R.A systematic experimental study on residence time distribution (RTD) in tubular flow was performed, covering a wide range of processing conditions. The flow of water in various sections of a tubular continuous thermal processing system was analysed using the classical Danckwerts approach. Methylene blue was used as tracer and different constant temperatures (25–80 °C) and flow rates (80–380 l/ h) were tested. T...
Residence time distribution of liquids in a continuous tubular thermal processi...
Torres, A. Pinheiro; Oliveira, F. A. R.The concept of efficiency of a holding tube is essential to guarantee the safety of continuously processed fluid foods. A good prediction of efficiency allows a better control of the processing conditions, guaranteeing product safety while decreasing product quality losses due to overprocessing. Different published methods were compared to data obtained in this work and to reported data, to assess their ability...
Residence time distribution studies in continuous thermal processing of liquid ...
Torres, A. Pinheiro; Oliveira, F. A. R.This paper presents a review on residence time distribution (RTD) studies in continuous thermal processing of liquid foods. The theoretical basis of the Danckwerts analysis is summarized, as well as the most important flow models, with special emphasis on tubular systems. Methods for experimental determination, modelling and estimation of RTD are critically described. While main design objectives in continuous ...
Development of perforation-mediated modified atmosphere packaging to preserve f...
Oliveira, F.A.R.; Fonseca, S.C.; Oliveira, J.C.; Brecht, J.K.; Chau, K.V.The use of perforations as a means of obtaining large size containers suitable for modified atmosphere packaging (MAP) would greatly enhance the applicability of this technology for storage and distribution of fresh and minimally processed products. General concepts of MAP, and advantages and drawbacks of using perforations to achieve it are discussed. Products for which perforated packages can be used are list...
Modelling of dissolved oxygen concentration during storage of packaged liquid d...
Ahrné, L. M.; Oliveira, F. A. R.; Manso, M. C.; Drumond, M. C.; Osted, R.; Gekas, V.A mathematical model that combines oxygen uptake from the outside environment with oxygen consumption by oxidative reactions, in a liquid packed food during storage, was developed. The model was applied to orange juice aseptically packaged in Tetra Brik Aseptic cartons, during storage of up to 5 months at 4, 8, 20, 30, 40 and 50 °C. The parameters of the model, the oxygen mass transfer coefficient and the rate ...
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