Effect of different drying methods on the drying characteristics, chemical properties and antioxidant capacity of Ziziphus jujuba var. Spinosa fruit

The fruit of Ziziphus jujuba var. Spinosa (ZJF) is a byproduct of the processing of the Suanzaoren commonly used in traditional Chinese medicine. Due to its high nutrient value, ZJF has been one of the most promising food sources. However, they are highly perishable, which severely limits the effective use of ZJF. To find a suitable drying method that facilitates the storage and processing of ZJF while maximizing the preservation of its nutrients and high biological activity, three drying methods, hot air drying (HD), infrared drying (ID), and vacuum drying (VD), were applied to ZJF samples at temperatures of 50, 60, and 70 °C in the present study. The drying kinetics, water activity, and content of active ingredients, including total polysaccharides (TPC), total flavonoids (TFC), total triterpene acids (TTAC), betulinic acid, oleanolic acid, ursolic acid, and antioxidant capacity were analyzed. The results showed that ID required the shortest drying time; with increasing temperature and time, the TPC decreased, the TTAC increased, and the TFC showed a dynamic trend. Furthermore, there was no significant difference between the samples and the antioxidant capacity. This study revealed that ID at 70 °C for 2 h is a suitable drying method for ZJF.