Browsing by Author "Calado, Ana Rita"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Analysis of the variations along drying of the physical-chemical properties of carrot.Publication . Calado, Ana Rita; Guiné, Raquel; Correia, Paula; Gonçalves, João CarlosDrying is one of the oldest preservation techniques for foods, and presently conventional hot air drying is among the most used techniques for food dehydration. Carrots are among the most common and popular vegetables throughout the world, because they provide valuable components indispensable for the development and proper functioning of the human body. They are very rich in β-carotene and vitamins of the B complex, being therefore considered a healthy food for human nutrition. This study aimed to determine the physical and chemical properties of carrots (Daucus carota L.) cv. Nantes, along drying by convection with hot air at three different temperatures (50, 60 and 70 ºC). The chemical properties evaluated were moisture content, protein, fibre, ash, sugars and water activity; and the physical properties were texture, colour, density and porosity. From the data obtained it was possible to conclude that the drying at 70 ºC originated more intense changes in the chemical properties analysed. For the drying at 70 ºC, moisture was reduced 93% in relation to the original value, proteins were reduced by 46% and ashes by 6%, while the total carbohydrates remained approximately constant. Concerning the textural properties, similar changes were found in terms of hardness, resilience, cohesion and chewiness. Particularly hardness and chewiness showed a sharp decrease in the early stages of drying. Hardness diminished from ~300 N to ~50 N and cohesiveness diminished from ~0.9 to ~0.7. Regarding the colour, it was observed a slight increase in lightness (L*) for all temperatures, while a* and b* remained approximately constant. The porosity increased along drying, due to the loss of moisture, varying from ~1% to ~6% (at 70 ºC) or to ~8% (at 50 and 60 ºC). The present work allowed concluding that drying of carrots at mild temperatures (50 or 60 ºC) does not produce very intense changes in the chemical properties, although the alterations at the physical level are evident.
- Evaluation of thermo-physical properties and drying kinetics of carrots in a convective hot air drying systemPublication . Guiné, Raquel; Gonçalves, João Carlos; Calado, Ana Rita; Correia, PaulaThis paper presents an experimental study on the evolution of carrot properties along convective drying by hot air at different temperatures (50ºC, 60ºC and 70ºC). The thermo-physical properties calculated were: specific heat, thermal conductivity, diffusivity, enthalpy, heat and mass transfer coefficients. Furthermore, the data of drying kinetics were treated and adjusted according to the three empirical models: Page, Henderson & Pabis and Logarithmic. The sorption isotherms were also determined and fitted using the GAB model. The results showed that, generally, the thermo-physical properties presented a decline during the drying process, and the decrease was faster for the temperature of 70ºC. It was possible to verify that the Page model presented the best prediction ability for the representation of kinetics of the drying process. The GAB model used to fit the sorption isotherms showed a good prediction capacity and, at a given water activity, despite some variations, the amount of water sorbed increased with the decrease of drying temperature.
- Time Evolution of Physicochemical Properties of Carrots During the Drying ProcessPublication . Calado, Ana Rita; Gonçalves, João Carlos; Correia, Paula; Guiné, RaquelThis study is aimed to determine the properties of Nantes carrots while drying by hot air at three different temperatures (50, 60 and 70 ºC). The chemical properties evaluated were: moisture, pro- tein, fibre, ash, sugars and water activity, and the physical properties were: texture, color, density and porosity. The results showed that the drying at 70 ºC affected mostly the chemical properties analyzed. Regarding the texture, similar changes were recorded in terms of hardness, gumminess and chewiness at the temperature of 70 ºC that affected these properties the most. Regarding color, in general the vari- ations in a* and b* along drying were not meaningful, although some discoloration was observed (in- crease in L*). The porosity increased due to the decrease in humidity. The final porosity measured for the carrots dried at 70 ºC was; however, lower than those for 50 and 60 ºC.