Percorrer por autor "Brandão, Teresa R. S."
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- Mathematical Models for Prediction of Temperature Effects on Kinetic Parameters of Microorganisms’ Inactivation: Tools for Model Comparison and Adequacy in Data FittingPublication . Gil, Maria M; Miller, Fátima A.; Brandão, Teresa R. S.; Silva, Cristina L. M.Microbial inactivation often follows a sigmoidal kinetic behaviour, with an initial lag phase, followed by a maximum inactivation rate period and tending to a final as ymptotic value. Mathematically, such tendencies may be de scribed by using primary kinetic models (Gompertz based model is one example) that describe microbial survival throughout processing time when stressing conditions are ap plied. The parameters of kinetic models are directly affected by temperature. Despite the number of mathematical equa tions used to describe the dependence of the kinetic parame ters on temperature (so-called secondary models), there is a lack of studies regarding model comparison and adequacy in data fitting. This work provides a review of mathematical models that describe the temperature dependence of kinetic parameters related to microbial thermal inactivation. Regression analysis schemes and tests seeking model compar ison are presented. A case study is included to provide guid ance for the assessment of secondary model adequacy and regression analyses procedures. When modelling temperature effects on sigmoidal inactivation kinetics of microorganisms, one should be aware about the regression methodology ap plied. The most adequate models according to the two-step regression methodology may not be the best selection if a global fit is applied.
- On the Use of the Gompertz Model to Predict Microbial Thermal Inactivation Under Isothermal and Non-Isothermal ConditionsPublication . Gil, Maria M.; Miller, Fátima A.; Brandão, Teresa R. S.; Silva, Cristina L. M.Food processes should be designed to provide an adequate margin of safety against microbiological risk of food poisoning and food spoilage throughout shelf life. In this field, the use of mathematical models that describe the microorganisms’ kinetics in such conditions is an important tool for convenient design, control and optimization of efficient processes. If those models are accurate and precise, one can extract the best aiming at predictive purposes. The Gompertz equation is commonly applied to describe sigmoidal kinetics. Besides the proven adequacy of the model in those kinetics descriptions, most of the reported works do not use Gompertz equation in the most convenient form, and insightful information could be obtained with re-parameterized forms. This work aims at reviewing the use of the Gompertz model to describe inactivation, as well as re-parameterized forms that include parameters related to the survival curve features. Microbial survival often presents a shoulder prior to inactivation, followed by a linear phase (corresponding to a maximum inactivation rate) and a tail residual population. The versatility of the Gompertz model in describing kinetics with different shapes, varying from a log-linear tendency till a complete sigmoidal shape, makes it attractive for predictive purposes, both under static and dynamic temperature conditions. Drawbacks and critical features of the model, when it is applied to microbial responses, will be overview.
- Quality changes of carrots under different frozen storage conditions: A kinetic studyPublication . Gonçalves, Elsa M.; Abreu, Marta; Pinheiro, Joaquina; Brandão, Teresa R. S.; Silva, Cristina L.M.In order to improve the overall quality of frozen carrots (Daucus carota L.), the degradation kinetics of several attributes were quantified during frozen storage under isothermal and nonisothermal conditions. The experimental results showed that the analyzed quality parameters were significantly affected by both tested frozen regimes. For both storage conditions, the degradation of color parameters and drip loss followed zero-order kinetics, and the texture was successfully described by a fractional kinetic model. A first-order kinetic model was adequate in describing total vitamin C decay under isothermal storage conditions. The storage temperature effect was adequately modeled by the Arrhenius law. The carrots shelf life under isothermal storage conditions of −18°C, using a threshold of 50% vitamin C content, will be of 118 days. Practical applications: The objective of this work was to evaluate the degradation kinetics of several quality attributes of carrots when subjected to various frozen storage temperature conditions that may occur along the distribution chain. The quality attributes degradation mechanisms are governed by chemical and/or physical changes that need to be systematically evaluated for further incorporation into product and process designs. The achieved results will be an insight to help manufacturers to predict and optimize products quality and determine its shelf life.