Moisture sorption isotherms, heat of sorption and properties of sorbed water of raw bamboo (Dendrocalamus longispathus) shoots

Moisture sorption isotherms of raw bamboo shoot were determined by static gravimetric technique based on isopiestic transfer of water vapor at 20, 30 and 35 °C. Inorganic saturated salt solutions in the range of 11.2-97.2% were used to create the required controlled humidity environment in a closed chamber. In the study, the sorption isotherms obtained were of sigmoid shape and of BET II type classification. Out of three sorption models i.e., BET, Caurie and GAB, fitted to the experimental data, Caurie model was found superior in interpreting the moisture sorption characteristics of bamboo shoot at three temperatures. The monolayer moisture content Mm as estimated by the best fitted Caurie's model for the sorption processes were 6.012%, 5.801%, 5.014%, and 5.987%, 5.816%, 4.998% (dry basis) at 20, 30, and 35 °C, respectively. The isosteric heats of sorption for both the adsorption and desorption process of bamboo shoots were found to increase with decrease in moisture content suggesting endothermic reaction at lower moisture content and it approached the value of heat of vaporization of free water at higher moisture content.

Research highlights▶ Moisture sorption isotherms of raw bamboo shoot were determined by static gravimetric technique at 20 °C, 30 °C, and 35 °C. Inorganic saturated salt solutions in the range of 11.2-97.2% were used to create the required controlled humidity environment. ▶ The adsorption and desorption isotherms obtained were of sigmoid shape and of BET II type classification. Out of three sorption models i.e., BET, Caurie and GAB fitted to the experimental data, Caurie model was found superior in interpreting the moisture sorption characteristics of bamboo shoot at three temperatures. ▶ The monolayer moisture contents as estimated by the best fitted Caurie's model for sorption processes were 6.012%, 5.801%, 5.014%, and 5.987%, 5.816%, 4.998% (d.b.) at 20, 30, and 35 °C, respectively. ▶ Hysteresis was observed over the entire range of water activity. The isosteric heat of sorption of bamboo shoot was found to increase with decreasing moisture content suggesting endothermic reaction at lower moisture content and at higher moisture contents it approached the value of heat of vaporization of free water.