Convective drying of onion: Kinetics and nutritional evaluation.
2010
Mota, C | Luciano, Cláudia | Dias, Ana | Barroca, Maria João | Guiné, Raquel
The present work aimed, on one hand, to study of the drying of onions in terms of drying kinetics, which was evaluated at 30ºC, 50ºC and 60 ºC. The experimental data was fitted to different empirical kinetic models from literature, and this kinetic study was then complemented with the modelling if terms of Fick’s diffusion equation, for estimation of the diffusion coefficients. On the other hand, the chemical characterization in fresh and after drying at different temperatures (varying from 30 to 70 ºC) was analysed, to evaluate the effect of drying and drying temperature on the chemical composition of the product. In this way, the analyses made were: moisture content, sugar content, crude protein, ash, fat, crude fibre, acidity and vitamin C. From the results obtained it was verified that some chemical components of the onions are not affected by drying (ash, fat, protein, fibre) whereas some others are considerably influenced by drying (sugars, acidity and vitamin C). The present work allowed to conclude that the three empirical models tested (Newton, modified Page and Logarithmic) all describe relatively well the dehydration kinetics at the three temperatures analysed. Moreover, from the experimental data was possible to estimate the diffusivities, which range between 3.33x10-09 m2/s at 30ºC and 8.55x10-09 m2/s at 60ºC.
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