Influence of Different Drying Techniques on Phenolic Compounds, Antioxidant Capacity and Colour of Ziziphus jujube Mill. Fruits

This study was to present the effect of different parameters of combined methods of drying such as vacuum-microwave (VMD: 480, 120 W), hot air (CDD: 70, 60, 50 °C) and combined methods as pre-drying by CD and finish drying by VMD (CD-VMD: 60 °C + 480/120W) in order to avoid a rapid increase in temperature at the critical moisture content of ca. 1 kg/kg dm (dry mass). Control samples were prepared by freeze-drying (FD). Drying kinetics, including the temperature profile of dried material, as well as on some quality factors of the finished product as phenolic compounds, antioxidant capacity, and color were evaluated. The increase in air temperature during CD as well as the increase in material temperature during VMD deteriorated dried product quality in terms of the content of phenolic compounds, antioxidant activity and color. Dried jujube fruits have a long shelf life and therefore may be a fine alternative to fresh fruit all year round.