Browsing by Author "Henriques, Francisca"
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- Chemical properties of pumpkin dried by different methods.Publication . Henriques, Francisca; Guiné, Raquel; Barroca, Maria JoãoINTRODUCTION Pumpkin is originated from America and belongs to Cucurbitaceae family. This fruit/vegetable has a huge nutritional and health protective value. Fresh pumpkins are very sensitive to microbial spoilage, even when refrigerated, being sometimes convenient to freeze or dry them. Drying is a method that allows the maintenance of nutritive properties of pumpkins and also has the capability to extend their life Presumably, drying process is the oldest and the most important method of food preservation. The main objective of drying consists in removing water in the solids up to a certain level, at which microbial spoilage and deterioration chemical reactions are much minimized. Freeze drying is considered a high technique of excellence and guarantees a higher quality of the product. METHODOLOGY In the present work the drying treatments used were convective air drying in a tunnel and a chamber at different temperatures, and freeze-drying. The chemical properties of the fresh and dried samples were evaluated in terms of ash, sugars (reducing, non-reducing and total), fiber and vitamin C, using established methodologies (AOAC). The phenolic compounds and antioxidant activity were assessed using a spectrophotometer to read the absorbencies of the methanol and acetone extracts. RESULTS AND DISCUSSION The results show that drying influences the sugars contents, and vitamin C in a high extent. The values for phenolic compounds and antioxidant activity are very identical for all samples, thus indicating that drying has a minor effect on the antioxidant capacity and in the phenolic compounds contents. However, some slight differences were observed. Furthermore, the acetone and methanol extracts also show some little differences. CONCLUSIONS The results obtained enable us to conclude that drying does not induce important changes, either in the phenolic contents or in the antioxidant activity.
- Efeito da secagem sobre a textura de peras da variedade Packhams.Publication . Henriques, Francisca; Marques, Bruno; Guiné, RaquelA textura é uma das características mais importantes no que diz respeito à qualidade dos alimentos, que, em conjugação com a aparência e sabor, tem grande influência na aceitação do produto alimentar por parte do consumidor (1). A textura caracteriza-se por um conjunto de propriedades físicas que são consequência da estrutura interna do material que por sua vez é determinada pelas interacções moleculares dos seus constituintes. Os alimentos no geral e as pêras em particular apresentam diferentes propriedades de textura. Estas derivam das diferenças inerentes às diferentes variedades, diferentes estados de maturação e aos métodos de processamento sofridos, neste caso a secagem (2). Neste trabalho, são objecto de estudo as pêras da variedade Packams, em fresco, secadas em estufa com convecção de ar a uma temperatura de 50 ºC, liofilizadas e rehidratadas, de forma a determinar as propriedades físicas de textura nos diferentes estados (frescas e secadas) e consequentemente fazer a respectiva análise e comparação dos resultados obtidos. O objectivo deste estudo prende-se por um lado, com a aquisição de conhecimento científico acerca das modificações ocorridas ao nível das propriedades de textura na pêra Packams, antes e depois do processo de secagem e, por outro lado, compreender o efeito que a desidratação tem nas diferentes propriedades de textura desta variedade de pêra. O método de secagem utilizado neste trabalho foi a secagem em estufa com circulação de ar a uma temperatura constante de 50ºC e pretendeu-se que o ponto final da secagem das pêras ocorresse para teores de humidade de cerca de 20%. A Liofilização foi efectuada num liofilizador, a partir das peras congeladas, a uma pressão de cerca de 0,7 Pa e uma temperatura à volta de – 50 ºC. As propriedades de textura foram avaliadas pelo método de análise do perfil de textura (TPA), utilizando como instrumento de medida um texturómetro. Esta análise foi efectuada para as mesmas pêras antes e depois da secagem. Os parâmetros de textura avaliados foram a dureza, a adesividade, a coesividade, a elasticidade e a mastigabilidade.
- Influence of Drying Treatment on Physical Properties of PumpkinPublication . Henriques, Francisca; Guiné, Raquel; Barroca, Maria JoãoThe aim of this work was to evaluate the properties of pumpkin (Cucurbita maxima L.) exposed to convective air drying and freeze-drying. The samples were analyzed in terms of physical properties (colour and texture). The trials in the convective chamber were done at 40 ºC and 60 ºC, in the drying tunnel at 60 ºC and in the freeze dryer at -50 ºC. It was concluded that the freeze drying and the air drying at 40 ºC produced smaller changes in the colour while the drying in the tunnel originated more intense colour changes. With respect to texture, it was possible to deduce that the pulp in the fresh product at 2 cm off from the skin is harder than the pulp at 4 cm off from the skin. As to the effect of drying in the texture of the pumpkin, it was observed that all dryings affected texture considerably when compared to the fresh product. In fact, hardness varied from 75 % in the drying in chamber at 40 ºC to 90 % in the tunnel drying, when compared to the fresh product. As to springiness, it was changed more in the drying at 40 ºC, while cohesiveness showed the higher change in the freeze drying treatment.
- Influence of drying treatment on physical properties of pumpkinPublication . Henriques, Francisca; Guiné, Raquel; Barroca, Maria JoãoINTRODUCTION Pumpkin is widely used in soups, sauces, packed food and desserts. Its colour, shape, size, texture and appearance varies widely, according to species. Pumpkins are a good source of carotene, water-soluble vitamins and amino acids. Drying is important for preservation in industrial and agricultural applications. However, the food may be exposed to temperatures that have an adverse effect on quality. Some properties that are appreciated by consumers are visual appearance (including colour), taste, odour and texture. Instrumental texture profile analysis (TPA) is one of the methods to determine the texture by simulating or imitating the repeated biting or chewing of a food. METHODOLOGY The present work evaluates the effect of different dryings on some physical properties of pumpkin, namely colour attributes and textural properties. The drying treatments used were convective air drying in a tunnel and a chamber at different temperatures, and freeze-drying. The colour was determined using a colorimeter. The CIELab system was used: L*=brightness (0-black, 100-white), a*=green-red balance (negative-green, positive-red), b*=blue-yellow balance (negative-blue, positive-yellow). The texture was assessed by texture profile analysis, and the textural parameters were calculated. RESULTS AND DISCUSSION From the results obtained, it is possible to conclude that freeze drying turns the product lighter, although the other colour parameters practically do not change. On the other hand, increasing temperature induces more intense colour changes, for the convective dryings. With respect to texture, important variations were found in the firmness of the pulp from the fresh state to the various dried ones, and that increasing temperature is responsible for increasing firmness. As to the freeze drying treatment, the changes produced in firmness are less intense. CONCLUSIONS The results obtained enable us to conclude that the freeze drying was the treatment that produced products with properties more similar to the fresh pumpkin, thus allowing preserving the characteristics of this food product.
- Influence of drying treatment on the physical and chemical properties of cucumber.Publication . Henriques, Francisca; Guiné, Raquel; Barroca, Maria JoãoThe present study evaluates the effect of drying treatments such as convective air drying and freeze-drying on the colour, texture, chemical properties (ash, sugars, fibre and vitamin C), phenolic compounds and antioxidant activity of cucumber. The trials in the convective chamber were done at 40 ºC and 60 ºC, in the drying tunnel were done at 60ºC and in the freeze dryer were done at -50ºC. It was possible to conclude that the air drying at 60 ºC (drying chamber and drying tunnel) produces small changes in colour of cucumber whereas air drying at 40 ºC and freeze drying originate more intense colour changes. With relation to texture it has been possible to deduce that the skin is harder than the peel in the fresh product, and that increasing drying temperature increases the hardness of the peel. In terms of ashes it was possible to verify that all values are similar but the value more similar to the fresh product was the one dried at 40ºC. The sugars contents (reducing, non reducing and total), were higher for the freeze drying and the trials for air drying at 60ºC (chamber and tunnel). Regarding fibres, it was found out that the higher value was obtained for air drying at 60ºC and the lower for freeze drying. In terms of vitamin C it has been possible to conclude that all treatments have a very pronounced effect in its reduction. In terms of antioxidant activity and phenolic compounds it is possible to verify that the different drying treatments are quite similar and do not produce significant reductions as compared to the fresh product.
- Influence of drying treatments on the physical and chemicalPublication . Guiné, Raquel; Henriques, Francisca; Barroca, Maria JoãoThis work aimed at determining the properties of cucumber exposed to convective air drying and freeze- drying. The samples were analysed in terms of colour, texture, chemical properties (moisture content, fibre, ash, vitamin C and sugars), phenolic compounds and antioxi- dant activity in fresh and after drying. The trials in the convective chamber were done at 40 and 60 C, in the drying tunnel at 60 C and in the freeze dryer at -50 C. The results showed that the antioxidant activity and the phenolic compounds were not affected by any of the drying treatments tested, since the values were quite similar in the fresh product as compared to the dried cucumbers. With respect to colour, the freeze drying treatment was identified as the one originating less colour change, when compared with the colour of the fresh product. Finally, texture was less affected by drying in the chamber at 40 C and freeze drying.
- Mass transfer coefficients for the drying of pumpkin (Curcubita moschata) and dried product quality.Publication . Guiné, Raquel; Henriques, Francisca; Barroca, Maria JoãoThe aim of this work was to determine the mass transfer properties of pumpkin (Cucurbita moschata) exposed to air drying. The drying temperatures tested ranged between 30ºC and 70ºC, and the kinetic behaviour was studied in this temperature band. The samples were analyzed in terms of moisture content, acidity, proteins, lipids and crude fiber, both in the fresh state and after drying. From the chemical analyses made it was possible to conclude that drying induces some reductions in acidity, lipids, fibers and proteins. As to the influence of the drying temperature on the process, it was observed that a temperature rise from 30 ºC to 70 ºC led to a 70 % saving in drying time. The results obtained by fitting the experimental data to the kinetic models tested allowed concluding that the best model for the present case is Henderson-Pabis, and the worst is Vega-Lemus. Furthermore, in this work it was possible to determine the values of the diffusion coefficient at an infinite temperature, De0, and activation energy for moisture diffusion, Ed, which were, respectively, 0.0039 m2/s and 32.26 kJ/mol. Similarly the values of the Arrhenius constant and the activation energy for convective mass transfer, respectively hm0 and Ec, were also calculated, being the first 3.798x108 m/s and the later 86.25 kJ/mol. These results indicate that the activation energy for convective mass transfer is higher than that for mass diffusion.
- O Papel dos ácidos gordos na nutrição Humana e desenvolvimentos sobre o modo como influenciam a saúdePublication . Guiné, Raquel; Henriques, FranciscaAo longo dos tempos tem-se verificado que os ácidos gordos fazem, cada vez mais, parte da alimentação, independentemente do continente, país e/ou cultura. Estes ácidos englobam vários constituintes e cada um deles tem a sua especificidade. Os ácidos gordos mais importantes são os essenciais, caso do omega-3 e do omega-6, e desempenham um papel bastante significativo na saúde humana. Além disso, é necessário referir que desempenham funções de protecção, redução de risco e de inflamação em relação a determinadas doenças, tais como asma, cancro, hipertensão, lúpus, doenças de pele e oculares, depressão, entre outras. Segundo alguns estudos realizados, a maior parte destes efeitos está comprovada, mas nem todos os casos estão ainda cientificamente aceites e existem casos em que, muitos dos autores entram em “conflito” devido a divergência de opiniões, por via de resultados eventualmente contraditórios obtidos em estudos quer “in vitro” quer “in vivo”. É, então, necessário verificar e comprovar todos estes potenciais efeitos, no sentido de verificar que os ácidos gordos, provavelmente, na sua maioria, podem funcionar muitas vezes como nutracêuticos ou complementar uma medicação em variadas situações.
- O Papel dos Ácidos Gordos na Nutrição Humana e Desenvolvimentos Sobre o Modo Como Influenciam a SaúdePublication . Guiné, Raquel; Henriques, FranciscaAo longo dos tempos tem-se verificado que os ácidos gordos fazem, cada vez mais, parte da alimentação, independentemente do continente, país e/ou cultura. Estes ácidos englobam vários constituintes e cada um deles tem a sua especificidade. Os ácidos gordos mais importantes são os essenciais, caso do omega-3 e do omega-6, e desempenham um papel bastante significativo na saúde humana. Além disso, é necessário referir que desempenham funções de protecção, redução de risco e de inflamação em relação a determinadas doenças, tais como asma, cancro, hipertensão, lúpus, doenças de pele e oculares, depressão, entre outras. Segundo alguns estudos realizados, a maior parte destes efeitos está comprovada, mas nem todos os casos estão ainda cientificamente aceites e existem casos em que, muitos dos autores entram em “conflito” devido a divergência de opiniões, por via de resultados eventualmente contraditórios obtidos em estudos quer “in vitro” quer “in vivo”. É, então, necessário verificar e comprovar todos estes potenciais efeitos, no sentido de verificar que os ácidos gordos, provavelmente, na sua maioria, podem funcionar muitas vezes como nutracêuticos ou complementar uma medicação em variadas situações.
- Valorização de pepino através de secagem: estudo do efeito do método de secagem sobre a composição fenílica e actividade antioxidante do produtoPublication . Guiné, Raquel; Henriques, Francisca; Barroca, Maria João: O presente estudo avalia o efeito dos tratamentos de secagem, como é o caso da secagem em câmara convectiva, secagem de túnel e liofilização sobre as propriedades químicas de pepino (actividade antioxidante e compostos fenólicos) em comparação com o produto em fresco. Os ensaios da secagem em câmara convectiva foram realizados a 40ºC e a 60ºC, a secagem de túnel foi realizada a uma temperatura aproximada de 60ºC e a liofilização com uma temperatura de cerca de -50ºC. É possível concluir que no pepino, tanto em fresco como após as várias secagens mencionadas, as alterações da actividade antioxidante e dos compostos fenólicos não são significativas, mostrando que apesar das altas temperaturas a que o pepino foi sujeito, os valores obtidos são muito semelhantes entre si.