Thermodymnamic properties of crambe fruits

ABSTRACT. This study aimed to determine and evaluate the thermodynamic properties of crambe fruit at different equilibrium moisture contents. The dynamic-gravimetric method was used to collect experimental data. Crambe fruits with an initial moisture content of approximately 26% db (dry basis) were used. The thin-layer desorption of the product was conducted at different controlled temperatures (25, 30, 35, 40, and 45°C) and at water activity levels ranging from 0.10 to 0.89 until the product reached the equilibrium moisture content at the specified air condition. In conclusion, the thermodynamic properties of crambe fruit are affected by temperature and moisture content. The isokinetic theory is valid for the desorption process, which is controlled by enthalpy, and the Gibbs free energy is positive at all of the tested temperatures, which indicates that water desorption is not a spontaneous process.

摘要：本研究旨在测定并评价不同平衡含水率（equilibrium moisture content）下海甘蓝果实的热力学特性（thermodynamic properties）。本研究采用动态重量法（dynamic-gravimetric method）采集实验数据，选用初始含水率（干基，dry basis）约为26% db的海甘蓝果实作为实验试样。对该试样开展薄层解吸（thin-layer desorption）实验，设置了25、30、35、40及45℃的控温梯度，水分活度（water activity）范围为0.10至0.89，直至试样在指定空气条件下达到平衡含水率。综上，海甘蓝果实的热力学特性受温度与含水率的共同影响。等动力学理论（isokinetic theory）适用于该由焓（enthalpy）调控的解吸过程；且在所有实验温度下，吉布斯自由能（Gibbs free energy）均为正值，表明水分解吸并非自发过程（spontaneous process）。