Browsing by Author "Cruz, AC"
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- Study of chemical and physical properties of apples dried in a convective drier.Publication . Cruz, AC; Guiné, Raquel; Gonçalves, JC; Correia, ACThe present study evaluates the effects of drying on apple slices from two varieties, Golden Delicious and Granny Smith, which were analyzed in terms of physical and chemical properties. The tests involved the determination of moisture, acidity, soluble solids, colour and texture. Trials were performed in a convective hot air dryer for different temperatures of 30, 40, 50 and 60 ° C. The results showed that the final moisture of the two varieties of apples was around 3 % (wet basis). With regards to acidity, the variety Granny Smith was found to be more acid than the Golden Delicious. The soluble solids are present, in general, in greater amounts in the variety Granny Smith. As to the colour, this varied very considerably from the fresh apples to the dried ones. Apples of the variety Golden Delicious presented a higher intensity of yellow (b* > 0) and red (a* > 0). However, in comparison to the variety Granny Smith the Golden Delicious presents, in general, smaller total colour differences. The textural attributes evaluated were hardness, adhesiveness, elasticity, cohesiveness and chewiness. However, the results for adhesiveness were very close to zero showing that these products do not have adhesiveness, as it happens with other fruits. It was also found that the fresh apples have a much higher hardness, when compared to the dried samples. Elasticity, on the other hand, was kept approximately constant regardless of the variety or state. Cohesiveness was higher in the fresh apples, and for the dried ones was higher for variety Golden. Finally, chewiness was higher for the fresh apples in comparison to the dried ones, and was higher for Golden Delicious when compared with Granny Smith.
- Study of the drying kinetics for apples in a convective drierPublication . Cruz, AC; Guiné, Raquel; Gonçalves, JC; Correia, ACIn the present work a convective drier was used to dehydrate apple slices up to a moisture content of less than 2 % (wet basis), so as to obtain a crunchy apple snack. Two commercial varieties were tested, namely Golden and Smith. The drier was operated at different temperatures, 30, 40 50 and 60 ºC, and the moisture content of the product was calculated based on the mass, which was registered by means of a data logger, throughout the whole trial. The kinetic data was then treated and fitted to different thin layer models frequently cited in literature, which were: Page, Henderson and Pabis, Logarithmic and Vega-Lemus. Others were also tested, but convergence was not achieved. For the fitting software SigmaPlot V8.0 (SPSS, Inc.) was used, and to evaluate the quality of the estimations the correlation coefficient (R) and the standard error of the estimate (SEE) were determined From the models tested it was possible to see that the Vega-Lemus was the worst to describe the drying kinetic in the present case, on the other hand, the best model was the Page. Also the Fick’s equation for diffusion was used to estimate the diffusivities at different temperatures, and from those to estimate the activation energy for moisture diffusion, which was found to be 35 kJ/mol for the drying of apples from Golden variety and 33 kJ/mol for the Smith variety.