Abstract Heat pump drying (HPD) has been used as one of the promising drying methods in food industry. To understand the color improvement and shrinkage inhibition of jujube slices during HPD, water state and glass transition temperature (Tg) were determined, macroscopic state diagram was further established. Jujube slices dried by HPD presented significantly lower color difference (ΔE) and shrinkage ratio than hot air drying. The temperature difference (ΔT = T-Tg) between the material temperature (T) and Tg showed significant effect on color and shrinkage of jujube slices. As the value of ΔT reduced, the ΔE change of jujube slices decreased. Tg increased significantly with the decrease of immobilized water. With the increase of Tg, solid matrix mobility of jujube slices decreased and the shrinkage tended to be stable. Macroscopic state diagram showed that critical moisture content of jujube slices dried by HPD which glass transition would happen at 25 °C was 0.061 g/g.

中文翻译：

---

通过水态和玻璃化转变了解热泵干燥过程中枣片外观质量的改善

摘要 热泵干燥（HPD）已被用作食品工业中一种很有前途的干燥方法。为了解枣片在HPD过程中的颜色改善和收缩抑制，测定了水状态和玻璃化转变温度（Tg），进一步建立了宏观状态图。与热风干燥相比，HPD 干燥的枣片呈现出显着更低的色差（ΔE）和收缩率。料温(T)与Tg的温差(ΔT=T-Tg)对枣片的色泽和收缩率有显着影响。随着ΔT值的减小，枣片的ΔE变化减小。随着固定化水的减少，Tg 显着增加。随着Tg的增加，枣片固体基质流动性降低，收缩趋于稳定。