龙眼果粉的水分吸附特性研究

Study on moisture sorption characteristics of longan powder

以龙眼果粉为对象,利用静态测量法测定其在不同温度下的吸湿等温线,探究在不同含水率下龙眼果粉的X射线衍射图谱及玻璃化转变温度,并通过数学方程计算其热力学特性参数,以揭示龙眼果粉的水分吸附特性。结果表明,龙眼果粉的吸湿等温线为Ⅲ型等温线,Peleg模型是龙眼果粉吸湿等温线的最佳拟合模型。在水分活度(water activity,A_(w))>0.69时,龙眼果粉水分吸附量显著增加,导致糖类晶体结构消失。龙眼果粉的吸附过程符合熵焓互补理论,其吉布斯自由能为1586.6 J/mol>0,表明可通过控制环境条件来控制龙眼果粉的吸附过程。干基含水率从0.054 g/g上升到0.350 g/g时,龙眼果粉的玻璃化转变温度起始点从14.6℃降低至-26.5℃,其终点从39.1℃下降至-5.8℃。25℃下龙眼果粉的理论最佳贮藏A_(w)为0.086,对应的干基含水率为0.0495 g/g。该研究结果可为龙眼果粉贮藏条件的选择提供参考。

This study focused on longan powder and used static measurement methods to determine its moisture sorption isotherms at different temperatures.The X-ray diffraction spectrum and glass transition temperature of longan powder at different moisture content were explored,and its thermodynamic properties were calculated through mathematical equations to reveal its moisture absorption characteristics.Results showed that the sorption isotherm of longan powder was typeⅢisotherm,and the Peleg model was the best-fitting model for the moisture sorption isotherm of longan powder.When water activity(A_(w))>0.69,the moisture absorption of longan powder increased significantly,which may be related to the disappearance of the sugar crystal structure.The sorption process of longan powder complied with the theory of entropy and enthalpy compensation theory,and its Gibbs free energy was 1586.6 J/mol>0,indicating that the sorption process of longan powder could be controlled by manipulating the environmental conditions.The initial glass transition temperature decreased from 14.6℃to-26.5℃and the end temperature decreased from 39.1℃to-5.8℃when the moisture content increased from 0.054 g/g to 0.350 g/g.The theoretical optimal storage A_(w) of longan powder at 25℃was 0.086,corresponding to a dry basis moisture content of 0.0495 g/g.The results of this study could provide a reference for the selection of storage conditions for longan powder.