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- Influence of pretreatments on quality parameters and nutritional compounds of dried galega Kale (Brassica oleracea L. var. acephala)Publication . Araújo, Ana C.; Oliveira, Sara M.; Ramos, Inês N.; Brandão, Teresa R. S.; Silva, Cristina L. M.The objective of this work was to evaluate the effect of six pretreatments on quality and nutritional contents of sliced Galega kale submitted to convective drying. Among all treatments, steam blanching was the most favourable, allowing improvements in retention of vitamin C, total antioxidant capacity and chlorophylls in comparison to the absence of pretreatment. Total phenolic losses were not reduced by steam blanching, but the retention was improved by combining this approach with a previous immersion in a metabisulphite solution. Moreover, steamblanching improved the colour parameters and appearance, providing a final dried product more similar to the fresh sample.
- Phytochemical and physicochemical properties of dried orange peel as affected by processing conditionsPublication . Phuon, Vichearavann; Brandão, Teresa R. S.; Ramos, Inês N.; Silva, Cristina L. M.
- Integrated approach on solar drying, pilot convective drying and microstructural changesPublication . Ramos, Inês N.; Brandão, Teresa R. S.; Silva, Cristina L. M.Solar drying of foods is an old technique, still used nowadays. Nevertheless, the mathematical approach of the complex phenomena involved is not completely integrated. Drawbacks appear in modelling heat transport, specially related to the huge variability of meteorological factors. The great dependence of the heat and mass transfer model parameters on water content is also frequently forgotten. Macroscopic changes (e.g. shrinkage) that occur during drying processes, are usually not considered in mass transfer equations, also affecting the predictive ability of the models. The objective of this work was to develop the mathematical basis and considerations for integrating heat and mass transfer phenomena, taking into consideration macroscopic changes and their correlation to changes at microscopic level (e.g. cellular shrinkage), that might occur during solar drying of grapes.
- Microwave and ultrasound pre-treatments for drying of the “Rocha” Pear: impact on phytochemical parameters, color changes and drying kineticsPublication . Onal, Begum; Adiletta, Giuseppina; Matteo, Marisa Di; Russo, Paola; Ramos, Inês Nunes; Silva, CristinaThe objective of this research was to evaluate the effect of drying temperature and innovative pre-treatments (i.e., microwave and ultrasound) on “Rocha” pear drying behavior and quality characteristics, such as color, total phenolic content and antioxidant activity. Experiments were carried out with pear slabs subjected to microwaves (2450 MHz, 539 W, 4 min, microwave oven) and ultrasounds (35 kHz, 10 min, in an ultrasonic bath) as well as control samples. The drying process was conducted in a tray dryer at three different temperatures (50, 55 and 60 °C) and a fixed air velocity of 0.75 m/s. Microwave technology resulted in a higher quality deterioration in dried pear samples compared to those of controls and ultrasound pre-treated samples. The combined application of ultrasound pre-treatment and the higher drying temperature of 60 °C was characterized by the lowest color changes (ΔE = 3.86 ± 0.23) and higher preservation of nutritional parameters (total phenolic content, TPC = 345.60 ± 8.99; and antioxidant activity, EC50 = 8.80 ± 0.34). The drying characteristics of pear fruits were also analyzed by taking into account empirical models, with the Page model presenting the best prediction of the drying behavior. In conclusion, ultrasound application is a promising technology to obtain healthy/nutritious dried “Rocha” pear snacks as dietary sources for consumers.
- Structural Changes During Air Drying of Fruits and VegetablesPublication . Ramos, I.N.; Brandão, Teresa R. S.; Silva, C. L. M.This work aims at reviewing structural changes occurring in convective air drying of fruits and vegetables. These include changes in physical properties, such as volume, porosity and bulk and particle density, which directlyaffect textural attributes of the products. Models relating with water content physical properties are also summarised. At microscopic level, the phenomena observed byprevious authors is described, focusing on shrinkage. In particular, a new approach on modelling kinetics of microstructural modifications is presented. Although the air drying process is relatively well studied, there is a lack of research concerning changes in structural properties. Modelling mass transfer during drying frequently does not include those effects and, there has not been established a standard methodologyfor predictive purposes. Correlating microstructure, texture measurements and sensoryanalysis would be an attractive area to be exploited for drying processes of fruits and vegetables. Although this is a wide working field, much is still to be done.
- Quantification of microstructural changes during first stage air drying of grape tissuePublication . Ramos, Inês N.; Silva, Cristina L.M.; Sereno, Alberto M.; Aguilera, José M.Microstructural changes in cells of Ruby grape (Vitis vinifera) quarters were monitored during first stage of convective air drying, under a stereo-microscope. A gradual overall shrinkage of grape cells was observed during the process. The cellular parameters: area, perimeter, major and minor axis length, Feret diameter, elongation, roundness and compactness, were quantified by image analysis. It was verified that cell dimensions suffered modifications during drying, but their shape remained unchanged. These microstructural changes showed a smooth exponential decrease with time, and a first-order kinetic model was satisfactorily fitted to the data. Temperature increased the rate of cellular shrinkage and this effect followed an Arrhenius type behaviour. Increasing temperature from 20 to 60 C resulted in a 350% increase of the area change rate. For the parameters related to cellular dimensions, the magnitude of the values were 10 3 min 1 for the rate of change at 40 C and 3 kJ/mol for the activation energy
- Effect of pretreatments on quality parameters and nutritional compounds of dried Galega kale (Brassica Oleracea L. Var. Acephala)Publication . Araújo, Ana C.; Oliveira, Sara M.; Ramos, Inês N.; Brandão, Teresa R. S.; Silva, Cristina L. M.Galega kale (Brassica Oleracea L. var. Acephala) is a vegetable quite common in several countries. It presents high moisture content at harvest, so it can only be preserved for a few days under room temperature. Therefore, drying processes can be employed to increase its shelf-life. However, drying exposes the product to high temperatures that can result in some losses of flavour, texture, colour and nutrients. To minimize these detrimental effects, several pretreatments may be used as possible strategies to improve nutritional attributes and sensory properties, after dehydration and during long-term storage. The objective of this work was to evaluate the effect of six pretreatments on quality and nutritional contents of Galega kale submitted to convective air drying. Water and steam blanching, simple or combined with chemical treatments, were applied to kale samples before convective drying. When compared to the absence of pretreatment, steam blanching provided improvements on retention percentages of 7.3 and 13.6% for vitamin C and total antioxidant capacity, respectively. Regarding pigments, steam blanching enabled higher retention of total chlorophylls. Total phenolic content was the only nutritional parameter in which steam blanching preceded by chemical treatment with metabisulfite provided better results than isolated steam blanching. Steam blanching for 1 min, without the need of previous chemical treatment, applied to kale samples before drying, demonstrated to be a valuable approach to reduce deterioration of the majority of the parameters in study, and also improved significantly the appearance of Galega kale after the drying process.