PRESERVATION OF CASHEW NUTS (Anacardium occidentale L.): WATER DESORPTION ISOTHERMS AND ISOSTERIC HEAT OF SORPTION

Abstract

Knowledge of a food product's sorption isotherms is of vital importance in determining its stability zone during storage. Thus, this study focuses on determining the desorption isotherms of cashew kernels at 40, 50 and 60°C. This was done experimentally, using solutions of increasing sulfuric acid concentration from 20 to 90%. Modelling was then carried out on the basis of eight (8) models described in the literature, using the non-linear GRG algorithm of the Excel 2021 solver. This was used to determine the net isosteric heat of desorption of cashew nuts. The experimental isotherms obtained have a type III sigmoidal shape. The BET model was used to calculate monolayer water contents of 3.07, 2.67 and 2.07% at 40, 50 and 60 °C respectively. Calculation of the correlation coefficient shows that Henderson's model has the highest coefficients (1 for 50 and 60 °C), with the exception of 40 °C, where Smith's model has the highest one (1 vs. 0.994 for Henderson). The net isosteric heat of desorption tends towards zero for high water contents (0.58 kJ/mol at 23.05% water). To guarantee good preservation of cashew nuts at 7% moisture content, the isosteric heat of the monolayer must be maintained at 0.79 kJ/mol.