Effects on the Drying Characteristics and Quality of Diospyros lotus L. by the Technology of Thermostatic and Subsection Temperature-Changing Hot Air Drying

To improve the quality and drying rate of Diospyros lotus L. under the hot-air drying technology, the effects of constant temperature and staged cooling hot-air drying process on its drying characteristics, heat-sensitive nutrients, sensory quality and rehydration were compared. The technique of subsection temperature-changing than thermostatic shortened the drying time by 1/4, which significantly improved quality of finished products. The optimized conditions of the subsection temperature-changing hot air drying were as follows: preheated at (40±1) ℃ for 15 min, reduced moisture content to 41.0%±0.5%, 37.0%±0.5% and 35.0%±0.5% at (68±1), (63±1) and (55±1) ℃, respectively. The content of total sugar, total phenol and V_C of dried Diospyros lotus L. were 49.53%±0.31%, (0.94±0.01) mg/g and (16.41±0.28) mg/100 g. The retention rate of nutrient substance were increased by 11.47%, 10.01% and 47.91%, respectively. Otherwise, drying rate increased to 18.75% and the sensory quality and re-hydration were better. Therefore, the product is easily accepted by consumers. The research results can provide theoretical basis and technical guidance for the industrial drying of Diospyros lotus L.