Dynamic vapour sorption isotherms and isosteric heats of sorption of two edible insects (Cirina forda and Rhyncophorus phoenicis)

Abstract

Cirina forda and Rhyncophorus phoenicis are widely consumed insects in tropical Africa. Drying is one of the main conservation techniques to improve the availability of these insects, which are harvested seasonally in the wild. The main goal of this study was to investigate the sorption isotherms and to estimate the shelf-life of these two dried insects. Sorption isotherms were determined at 25, 30, 40 and 50 °C by using dynamic vapour sorption. Amongst five isotherm sorption models that were selected to fit the experimental data, Peleg’s equation was found to give the best fit for both insect species. It was observed that all insects exhibited type III sorption isotherms, indicating monolayer-multilayer behaviour with a progressively decreasing biding energy as the number of layers rises. Using the Heiss-Eichner model, dry base initial moisture contents of 8 and 7%, are proposed for C. forda and R. phoenicis respectively. These conditions ensure a shelf-life of 12 months at 30 °C when insects are packaged in polyethylene films.