Water desorption isotherms for eleven varieties of dates

In this paper, we report on the water vapour desorption isotherms, at 25 degrees C, of eleven date (Phoenix dactylifera) varieties, from different locations, collected at full ripeness: Mech-Degla, Deglet-Nour and Haloua (Algeria), Barhi, Fardd, Khadrawi, Khalass, Madjol, Rizaz (Saudi Arabia), Madjhoul (Israel) and Kentichi (Tunisia). The static gravimetric method was used, according to the COST 90 recommendations. The overall shape of the curves describing the water content as function of the water activity was typical of sugar-rich materials. Experimental data were analysed using the Guggenheim-Anderson-Brunauer (GAB) and Brunauer-Emmett-Teller (BET) models, through direct non-linear regression without any transformation of data. Both models correctly fit the whole set of data, for water activity ranking from 0.11 to 0.90, but the BET model was preferred since the values of its parameters were more realistic. (C) 2000 Elsevier Science Ltd. All rights reserved.