Browsing by Author "Ferreira, Dulcienia"
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- Comparative study of the composition of pears dried under different methods.Publication . Loureiro, Andreia; Guiné, Raquel; Lima, Maria João; Ferreira, DulcieniaDrying of agricultural products under direct sunlight is the traditional way of preserving many fruits and vegetables. The use of the sun to dry foods has the advantage of being cheap. However there are some disadvantages, such as intensive labor and slowness of the process. Moreover, several factors make solar drying less attractive, such as: climatic conditions, product pollution from dust or from animal contamination, and other types of infestation and microbial or mould contamination in humid environments [1]. In Portugal, pears of the variety S. Bartolomeu (Pyrus communis L.) have been used to produce a traditional product named “pêra passa de Viseu”. These pears are dried at direct open air sun exposure, following a multi-step procedure. However, this procedure does not comply with modern quality standards, and therefore in the last years some investigation around this product and the production method has been carried out to better understand it and establish alternative production techniques [2], [3]. Among these alternatives, a solar stove with forced convection and a solar stove with natural convection were developed. In the present work pears of the variety S. Bartolomeu were dried following the traditional method at direct solar exposure and also inside the two stoves developed. The chemical properties were analyzed and quantified in the pears dried by the 3 systems, having in mind to find out which system allows the obtaining of a product more similar to the traditional pears. From the results obtained is possible to see that the drying carried out inside the solar stoves dos not produce fruits much different than those dried by the traditional method.
- Comparative study of the drying kinetics of pears for different drying systems.Publication . Almeida, Inês; Guiné, Raquel; Lima, Maria João; Ferreira, DulcieniaOpen-air sun drying has been used since immemorial times to dry grains, vegetables, fruits and other agricultural products. This is a common method used to preserve foods and it is practiced until today in many countries where the combination of solar radiation, temperature and relative humidity is appropriate. However, despite being a cheap method, the open-air natural sun drying is not always applicable to large-scale production [1]. “Pera Passa de Viseu” denominates a traditional food product produced from pears of the variety S. Bartolomeu (Pyrus communis L.) using a traditional solar drying method, which is based on an open-air exposure [2]. Notwithstanding being quite a cheap drying method, making use of the sun as energy source, it has some very important disadvantages, like for example, the process is slow and very much dependent on weather conditions, and the quality of the product is not satisfactorily taking into account factors such as pollution from dust or from animal contamination or other types of infestation and microbial or mould contamination in humid environments. Therefore, the development of alternative drying methodologies assumes a pivotal role. The pears used in the present study were dried uncut after peeling, in three different systems: solar stove with forced convection, solar stove with natural convection and drying tunnel. The moisture content of the pulp was quantified along drying with a Halogen Moisture Analyzer. The objective of the present work is to fit the kinetic data to different models found in literature to describe the drying rates of food products, in order to compare the drying rates in the different systems tested and also to find out which model is best to describe the drying kinetics of these pears.
- Influence of drying method on the colour of dried pears.Publication . Carrilha, Fátima; Guiné, Raquel; Lima, Maria João; Ferreira, DulcieniaColour is considered a fundamental property of foods, since it has been widely demonstrated that it correlates well with other physical, chemical and sensorial indicators of product quality [1]. In fact, colour plays a major role in the assessment of external quality in food industries and food engineering research. The measure of the standard colour of fruits and vegetables can be done by a wide range of colour spaces. However, the L*a*b* system is suggested as the best colour space for quantification in foods with curved surfaces [2]. Drying is one of the methods used for preserving foods, based on the removal of water to a level that minimizes microbial spoilage and deterioration reactions [3]. Pears of the variety S. Bartolomeu are traditionally dried in Portugal by a direct sun-exposure method. However, because of the disadvantages associated with this procedure, including not guarantying the sanitary quality and safety of the final product, in the past years alternative drying methodologies have been developed, such as solar stoves with natural or forced convection) and drying tunnel. In the present work pears of the variety S. Bartolomeu were dried under different systems and their colour was evaluated using a colorimeter in the L*a*b* mode, as recommended by the Commission Internationale de l’Eclairage (CIE). The objective of this study was to compare the colour of the fruits produced by the different systems to find out which one allows the obtaining of a product as much as possible with the same colour of the traditional pears. From the results obtained was possible to see that the drying carried out in the drying tunnel is the one that differs more from the traditional fruits.
- Influence of the drying method on the composition of dried pears.Publication . Guiné, Raquel; Lima, Maria João; Barroca, Maria João; Ferreira, DulcieniaIn Portugal, a traditional product named “Pêra Passa de Viseu” is made by direct open air sun exposure. However, this procedure does not comply with modern quality standards, and therefore in the last years some investigation around this product and the production method has been carried out to better understand it and establish alternative production techniques such as a solar stove, a solar drier and a drying tunnel. The chemical properties of the pears obtained by these methods were analyzed and quantified, trying to obtain a product more similar to the traditional one. The results show that the dryings carried out with sun exposure (inside glass) do not produce fruits much different than those dried by the traditional method.
- Properties of pears harvested at different ripening stages.Publication . Guiné, Raquel; Lopes, Pedro; Barroca, Maria João; Ferreira, DulcieniaPears of the variety S. Bartolomeu have been used over the years in Portugal to produce a traditional dried pear known as “pera passa”. The processing comprehends a solar drying performed at open air, with obvious disadvantages, either concerning the drying efficiency or the sanitary quality of the final product, taking into account that the products are exposed to multiple contamination agents. For these reasons, attempts have been made to study alternative production methodologies, including the use of solar stoves, among others. In the present work pears of the variety S. Bartolomeu which were harvested at three different moments, and therefore correspond to three different ripening stages, were dried in a solar stove and the evolution of some properties was monitored along the drying process. From the results obtained was possible to conclude that the pears harvested in the two first dates show quite similar trends through drying, while the pears harvested at the last date reveal a clear distinct behavior, allowing to infer that the ripening stage at harvest plays an important role in the subsequent drying operation.