Browsing by Author "Quintas, Mafalda"
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- Fresh-cut melon quality during storage: an NMR study of water transverse relaxation timePublication . Fundo, Joana F.; Amaro, Ana L.; Madureira, Ana Raquel; Carvalho, Alexandra; Feio, Gabriel; Silva, Cristina L. M.; Quintas, MafaldaMolecular mobility is a fundamental parameter which reflects the dynamic properties of food components and contributes to food degradation reactions comprehension. Fresh-cut fruits have become an important food market segment. However, processing of fruits promotes faster its physiological deterioration, biochemical changes and microbial degradation. The purpose of this work was to use NMR methodology as a tool to evaluate fresh-cut fruit quality, during storage at refrigerated conditions. The fresh-cut melon transverse relaxation time (T2) was measured for a period of 7 days of storage at 5 °C. The relationship between the obtained values, microstructure and quality parameters was investigated. In general, results show the existence of one class of water fluidity in the system, the one present in cells after processing. T2, a measure of this fluidity, is affected by the processing and storage time. Also, it is possible to find a close relationships between T2 and quality parameters of total colour difference (TCD), firmness and aw. As T2 increases TCD also increases, while firmness and aw decrease. These results highlight the usefulness of NMR methodology application in food science.
- Fresh-cut pear quality during storage; a NMR study of water transverse relaxation timePublication . Fundo, Joana; Carvalho, Alexandra; Feio, Gabriel; Silva, Cristina L. M.; Quintas, Mafalda
- Heating foods: integrating quality and safety in thermal processesPublication . Quintas, Mafalda; Brandão, Teresa R. S.; Silva, Cristina L. M.
- Heating foods: integrating quality and safety in thermal processesPublication . Quintas, Mafalda; Brandão, Teresa R. S.; Silva, Cristina L. M.
- Integrating quality and safety in thermal and non-thermal food processesPublication . Brandão, Teresa R. S.; Quintas, Mafalda; Silva, Cristina L. M.
- Modelling viscosity temperature dependence of supercooled sucrose solutions: the random-walk approachPublication . Quintas, Mafalda; Brandão, Teresa R. S.; Silva, Cristina L. M.; Cunha, Rosiane L.Sucrose and its supersaturated or supercooled solutions are of the utmost importance in areas as different as food and pharmaceutical industries or cryopreservation of biological systems. In the supercooled “state”, such amorphous solutions are fragile systems, presenting extremely high viscosity with decreased mobility of molecules, impairing experimental determinations at low temperatures (below critical temperature, Tc). This work proposes the random walk (RW) approach to study relaxation behavior in the supercooled melt, using only viscosity data at temperatures above Tc. For comparison purposes, the Vogel-Fulcher-Tamman (VFT) model was fitted to th data. The random walk approach is based on the distribution of molecular energies, thus having a theoretical support not found in the VFT model. The RW estimated parameters can be correlated with system characteristics, showing their dependence on water content or sucrose concentration. RW and VFT model description was evaluated from the mathematical and physical points of view, but the random walk model led to more consistent regression results and parameter estimates with improved precision
- Molecular mobility, composition and structure analysis in glycerol plasticised chitosan filmsPublication . Fundo, Joana; Fernandes, Rui; Almeida, Pedro M.; Carvalho, Alexandra; Feio, Gabriel; Silva, Cristina L. M.; Quintas, MafaldaThis study was developed with the purpose to investigate the effect of polysaccharide/plasticiser concentration on the microstructure and molecular dynamics of polymeric film systems, using transmission electron microscope imaging (TEM) and nuclear magnetic resonance (NMR) techniques. Experiments were carried out in chitosan/glycerol films prepared with solutions of different composition. The films obtained after drying and equilibration were characterised in terms of composition, thickness and water activity. Results show that glycerol quantities used in film forming solutions were responsible for films composition; while polymer/total plasticiser ratio in the solution determined the thickness (and thus structure) of the films. These results were confirmed by TEM. NMR allowed understanding the films molecular rearrangement. Two different behaviours for the two components analysed, water and glycerol were observed: the first is predominantly moving free in the matrix, while glycerol is mainly bounded to the chitosan chain.
- Molecular mobility, crystallinity and barrier properties of chitosan filmsPublication . Fundo, Joana F.; Silva, Cristina L. M.; Quintas, Mafalda
- Multiresponse modelling of the caramelisation reactionPublication . Quintas, Mafalda; Guimarães, Carla; Brandão, Teresa R. S.; Silva, Cristina L. M.
- Multiresponse modelling of the caramelisation reactionPublication . Quintas, Mafalda; Guimarães, Carla; Baylina, João; Brandão, Teresa R. S.; Silva, Cristina L.M.Multiresponse modelling is a powerful tool for studying complex kinetics of reactions occurring in food products. This modelling technique uses information of reactants and products involved, allowing insightful kinetic parameters estimation and helping in clarifying reaction mechanisms. One example of a complex reaction that occurs in food processing is the caramelisation reaction. Caramelisation is the common name for a group of reactions observed when carbohydrates are exposed to high temperatures. The objective of this work was to apply multiresponse regression in developing a mathematical mechanistic model that describes sucrose thermal degradation and caramelisation products formation in highly concentrated sucrose solutions, with different water contents and under various temperatures. Results demonstrated the usefulness of multiresponse modelling in understanding reaction mechanisms in food matrices. A mechanistic model for the caramelisation reaction was proposed, which successfully described the experimental data of concentrated solutions in the 30.03 to 12.20% (w/w) water content range. Furthermore, good predictions of temperature and water content effects were achieved. For extremely low water content systems (3.58% (w/w)), the proposed mechanistic model failed to describe experimental data, indicating different reaction pathways.