不同干制方式对枸杞粉吸湿过程中水分变化的影响

Effects of different drying methods on moisture changes in wolfberry powder during moisture absorption

以3种不同干燥方式下的枸杞所制得的粉体为研究对象,通过测定吸湿速率、吸附等温曲线探讨枸杞粉的吸湿规律,并利用低场核磁共振技术分析枸杞粉吸湿过程中的水分迁移特性。结果表明,3种干制方式下的枸杞粉吸湿等温曲线均属于Ⅲ型等温线,当水分活度大于0.5时,在同一水分活度下,其平衡含水率大小为,晒干>烘干>冻干,说明枸杞粉贮藏环境的水分活度低于0.5时较易保存;3种干制方式下的粉体储藏过程中,其核磁共振谱图显示,结合水(T_(21))随时间变化显著升高(P<0.05),不易流动水(T_(22))在前15 d没有显著变化,到第30天时显著升高(P<0.05),自由水(T_(23))无明显变化,说明在枸杞粉吸湿过程中,水分迁移变化主要发生在结合水与不易流动水之间;并发现储藏期在15 d之前,冻干方式所获得的枸杞粉吸湿特性更加稳定。该实验结果对于研究枸杞粉吸湿过程中的水分变化具有重要意义,同时为解释粉体吸湿机理提供理论依据。

The moisture absorption law of the wolfberry ( Lycium barbarum ) powder obtained by three different drying methods was determined by measuring the moisture absorption rate and adsorption isotherm curves. Low-field NMR technique was used to analyze the characteristics of moisture migration during moisture absorption process of the powder. The results showed that the moisture absorption isotherms of the wolfberry powder obtained by three different drying methods all belonged to type III isotherm. When the water activity was greater than 0.5, at the same water activity, the equilibrium water content was as follows: sun drying> heat-drying> freeze-drying, which indicated that wolfberry powder was easier to be stored when the water activity of the storage environment was less than 0.5. The NMR spectra showed that the powder made by three different drying methods had T 21 increased significantly with time ( P <0.05) during storage, while T 22 did not change significantly during the first 15 days and increased dramatically ( P <0.05) on day 30. There were no significant changes in T 23 , which indicated that the changes in moisture migration were mainly between bound water and immobile water during moisture absorption. It was found that the hygroscopicity characteristics of the powder obtained by freeze-drying was more stable in initial 15 days. These results are important for studying the moisture changes in Lycium barbarum powder during moisture absorption. This study also provided theoretical bases for explaining the mechanisms of moisture absorption of powder.