Drying characteristics of jujube (Zizyphus jujuba) slices in a hot air dryer and physicochemical properties of jujube powder

摘要

The hot air convective drying characteristics of sliced jujube fruits were investigated. Drying experiments were carried out at three different temperatures (60, 70 and 80 degrees C) and three different air velocity (0.5, 1.0, 1.5 ms(-1)). All drying experiments had only falling rate period. The average effective diffusivity values varied from 1.2x10(-9) to 3.55x10(-9) m(2)s(-1) over the temperature and velocity range studied and the activation energy was estimated to be 28.183 kJmol(-1) by modified Arrhenius Equation. In order to select a suitable form of the drying curve, seven different thin layer drying model was investigated and Page and Wangh and Singh models were considered the best to explain the drying of the jujube slices. Also, the influence of varied drying temperatures and velocity were investigated on physicochemical properties of the jujube powder. It was observed that moisture content and water activity values, which are an important powder product property, decrease with increasing temperature. It was found that the powder product obtained has different particle properties depending on the air temperature and velocity and therefore has different bulk and reconstitution properties. Within the scope of chemical analyzes, it was observed that the sugar content of the powder products is considerably high due to low moisture content. Also, according to the total phenolic content analysis, the higher temperature resulted in the lower total phenolic content.