Percorrer por autor "Ávila, Isabel M. L. B."
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- Development of a novel methodology to validate optimal sterilization conditions for maximizing the texture quality of white beans in glass jarsPublication . Ávila, Isabel M. L. B.; Smout, Chantal; Silva, Cristina L. M.; Hendrickx, MarcOptimal thermal processes were designed for white beans in glass jars heated in a still and end-over-end rotary pilot water cascading retort. For this purpose, isothermal kinetics of thermal softening of white beans were studied in detail using a tenderometer and a texturometer. The fractional conversion model was applied in both cases to model the texture degradation. The Arrhenius equation described well the temperature dependence of the reaction rate constant. With regard to the heat transfer, heat penetration parameters (fh and jh) were experimentally determined from 100 containers under static as well as rotational (end-over-end) conditions at 4, 7, 10, and 15 rpm. Theoretical optimal temperatures, maximizing volume average quality retention, were calculated using a computer program valid for conduction heating foods. Experimental verification of the calculated results was conducted. Considering the finite surface heat transfer coefficient, theoretical and experimental optimal temperatures were of the same order of magnitude, around 130 °C, while for an infinite surface heat transfer coefficient the calculated optimum temperature was much lower than the experimental value. The type of reaction kinetic model, fractional conversion or first-order models, does not significantly affect optimal sterilization temperatures. Although some differences were found, the developed theoretical approach was successfully applied to convective and mixed heating mode products. The use of the correct surface heat transfer coefficient is crucial to design optimal processing conditions.
- Methodologies to optimize thermal processing conditions: an overviewPublication . Ávila, Isabel M. L. B.; Silva, Cristina L. M.
- Modelling the thermal sterilisation of foods inside packs with two divisionsPublication . Ávila, Isabel M. L. B.; Manso, Maria da Conceição; Silva, Cristina L. M.A mathematical model was developed to describe the heat transfer during the sterilisation of conduction heating foods inside three dimensional two division rectangular packs. The model uses a standard explicit finite differences method with non-capacitance surface nodes and simulates different pack sizes, food properties and surface heat transfer resistances at the package lid and walls. Taking into account the cooling phase, the sterility value was calculated as a function of position in order to identify the location of the least lethality point. The most important variables affecting the position of this point are the product heating rate and the surface heat transfer coefficients. For low heating rate values this critical point moves towards the surface. When different food products are sterilised in simultaneously the quality degradation of foods in this type of package is also a point of discussion.