Effect of Microwave Vacuum Drying on the Drying Characteristics and Chemical Compositions of Turkish Gall Residues

Abstract

Recently, the secondary use of waste has received increasing attention. The raw material of Xipayi mouth rinse is Turkish gall. During the industrial production of Xipayi mouth rinse, a lot of gall residues are produced. If these drugs are directly discarded, it will cause waste of resources and also bring pressure to the ecological environment. Previous studies have found that the active ingredient content of Turkish gall residues remains high, therefore the residues are still a valuable resource for exploitation. This study aimed to evaluate the effect of the chemical compositions and drying characteristics of Turkish gall residues during microwave vacuum drying (MVD). Different vacuum degrees, sample loads and sample sizes were used to investigate the drying characteristics of Turkish gall residues, and a kinetics model was established to describe the drying characteristics. We determined gallic acid (GA), methyl gallate (MG) and ellagic acid (EA) contents, total phenolic content (TPC) and total sugar content (TSC) of dried Turkish gall residue powder and investigated the influence of different MVD conditions on components. The results showed the good fit of the Page model equation in describing the drying kinetics of Turkish gall residues during MVD. Different conditions of MVD have different effects on the main components of residue. Thus, MVD can be used to desiccate Turkish gall residues. The Page kinetics model predicts the changes in dehydration rate during MVD of Turkish gall residues, providing a proven drying method for gall residues, and provides a theoretical basis for the industrial mass production of pharmaceutical residues.