Modelling the dehydration kinetics of four onion varieties in an oven and a solar greenhouse

The Oven drying kinetics mathematical modelling of four Senegalese onion varieties is carried out in the temperature range from 50 °C to 70 °C. The R(2) (dispersion test) and the χ(2) (fit test) between the experimental data and the values predicted by the models show that whatever the temperature and the variety, the Verma et al. model is the one that best fits the oven drying kinetics. The R(2) average and χ(2) average values for the Galmi Violet, Safari, Gandiol F1 and Orient F1 are respectively between 0.9848 to 0.9961 and 0.0010 to 0.006. This best model is validated on the solar greenhouse drying kinetics at variable temperatures during the drying process. The Drying Characteristic Curves (DCCs) have identical patterns for the four onion varieties and are described with third order polynomials in the reduced moisture content range from 0.1 to 0.7. The Galmi Violet, with the slowest drying rate, is the limiting variety, followed by the Safari, Gandiol F1 and Orient F1. Furthermore, the critical and equilibrium reduced moisture content deduced from the DCCs are respectively between 0.55 to 0.70 and 0.05 to 0.15.