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

The water sorption isotherms of non-fermented (Venezuelan fine second grade) cocoa beans (Theobroma cacao) were determined at three temperatures typically found during storage in tropical countries (25°C, 30°C and 35°C). For this purpose the grounded samples were equilibrated in desiccators containing 17 saturated salt solutions of known aw at the temperatures studied, covering a range of aw from 0.08 to 0.94. The desiccators with the samples were kept in temperature-controlled incubators at the temperatures indicated above (±0.5°C). When equilibrium was reached, the moisture content and the aw of the samples were measured at the temperature of the experiment. The data obtained were adjusted to several regression models in order to determine the best fit. No statistical differences (α=0.01) were found among the isotherms of 25°C, 30°C and 35°C, being all data adjusted to a single isotherm in this temperature range. The BET equation showed the best fit for aw<0.50 (r=0.986) and the Harkins–Jura model for aw⩾0.50 (r=−0.986). The adjusted equations showed constants of 0.0149 for the intercept and 0.324 for the slope of the linearized BET equation and −0.0468 and −16.711 for the intercept and slope of the linearized equation of Harkins–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 model (r=0.970). An average sorption enthalpy value of 1.81±0.10 kcal/gmol was obtained for the temperature range studied (25–35°C).