Modeling Desorption Isotherms of Four Onion Varieties Related to Temperatures

Abstract

The sorption isotherm is useful for predicting changes in product stability and the choice of packaging. Therefore, this study aims to establish the desorption isotherm model of the Galmi Violet, Safari, Gandiol F1, and Orient F1 onion varieties related to temperature. The gravimetric method using saturated salt solutions was implemented to determine the desorption isotherms, whose modeling, based on empirical mathematical models, was carried out with MATLAB software 6.0.0 using the least squares method. The results show that the isotherms obtained are of type II. The equilibrium moisture content ( X eq ) decreases with increasing temperature, but the effect is smaller at the end of desorption for water activity values < 0.2 and X eq < 1 kg/kg db (Galmi Violet and Gandiol F1), <0.7 kg/kg db (Safari and Orient F1), and <0.4 kg/kg db (their mixture). It’s also shown that the Henderson model provided the best overall fit for all varieties and their mixture (R 2 between 0.97 and 0.99, χ 2 between 0.0016 and 0.0079), though other models also performed better for specific varieties: the Oswin model was the best for Galmi Violet (R 2 : 0.9915 and χ 2 : 0.0020) and the Peleg model was more suitable for Orient F1 (R 2 : 0.9956 and χ 2 : 0.0023). Furthermore, the desorption isotherm of the onion mixture closely resembled that of Safari between 50˚C and 60˚C, and Gandiol F1 at 65˚C. These findings suggest that drying and storage strategies for the mixture could be optimized based on these two varieties. Thus, model selection should consider both the specific variety and the intended use (individual or mixed).