Sorption isotherm and state diagram of grapefruit as a tool to improve product processing and stability Original Research Article

The sorption isotherm and state diagram of grapefruit have been constructed and modelled. Partially air-dehydrated and freeze-dried grapefruit was used to obtain samples in the range of freezable and non-freezable water content, respectively. The cooling curve and/or differential scanning calorimetry of the samples allowed freezing and glass transition temperatures to be obtained. The sorption isotherm was fitted to the BET (Brunauer, Emmett and Teller) and GAB (Guggenheim–Anderson–de Boer) models and the glass transition data to the Gordon and Taylor model. To predict the freezing curve, both generalized Norrish and Robinson and Stokes’ equations and an empirical model have been used. At water content greater than 0.19 g water/g sample, cooling the product to −31.2 °C and keeping it in frozen storage at below −50 °C will ensure its maximum stability. If only non-freezable water is present in the product, the more stable glassy state may be achieved at different temperature or water contents, which may be predicted from the obtained state diagram.