Onion drying: Kinetic study and chemical characterization.

Abstract

The present work aimed the experimental study of the drying kinetics of onions at constant temperature (40ºC, 60ºC and 70 ºC) to obtain the drying curves, which were then fitted to different kinetic models of moisture ratio from literature. The experimental data for the moisture ratio content with time was fitted using the software Sigma Plot, v8.0 (SPSS, Inc.). The study was complemented with the chemical characterization of the onions in fresh and after drying at the lowest and highest temperatures, for evaluation of 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, proteins, ash, fibre, acidity and vitamin C. The results obtained for the nutritive values of dried onion showed that the total sugars, vitamin C and acidity were lost during the drying process and their reduction was increased when temperature raised from 40ºC to 70ºC. Moreover, to obtain a similar safe moisture content the drying time was reduced about 70% when the temperature was increased from 40ºC to 70ºC.