Water sorption isotherms of non-fermented cocoa beans (Theobroma cacao)

The water sorption isotherms of non-fermented (Venezuelan fine second grade ) cocoa beans (Theobroma cacao) were determined at three temperatures typic ally found during storage in tropical countries (25 degreesC, 30 degreesC a nd 35 degreesC). For this purpose the grounded samples were equilibrated in desiccators containing 17 saturated salt solutions of known a(w) at the te mperatures studied, covering a range of a(w) from 0.08 to 0.94. The desicca tors with the samples were kept in temperature-controlled incubators at the temperatures indicated above (+/-0.5 degreesC). When equilibrium was reach ed, the moisture content and the a(w) of the samples were measured at the t emperature of the experiment. The data obtained were adjusted to several re gression models in order to determine the best fit. No statistical differen ces (alpha = 0.01) were found among the isotherms of 25 degreesC, 30 degree sC and 35 degreesC, being all data adjusted to a single isotherm in this te mperature range. The BET equation showed the best fit for a(w) < 0.50 (r = 0.986) and the Harkins-Jura model for a(w) <greater than or equal to> 0.50 (r = -0.986). The adjusted equations showed constants of 0.0149 for the int ercept and 0.324 for the slope of the linearized BET equation and -0.0468 a nd -16.711 for the intercept and slope of the linearized equation of Harkin s-Jura, respectively. In both cases the regression analysis showed a linear adjustment (P < 0.001). Mean values for water content of the monolayer of 2.94/100 g were determined with the BET model and 2.18/100 g with the GAB m odel (r = 0.970). An average sorption enthalpy value of 1.81 +/- 0.10 kcal/ gmol was obtained for the temperature range studied (25-35<degrees>C). (C) 2001 Elsevier Science Ltd. All rights reserved.