Optimization of Polygonum cuspidatum drying for the retention of primary effective composition

Abstract.

Objective In order to search a proper drying strategy for retaining the primary effective composition of polygonum cuspidatum, slice samples were dehydrated using three drying methods without any chemical preservative added. Vacuum freezing drying, microwave drying and air drying with different work conditions were used for sample dehydration. The product quality was evaluated with indicator compounds, consisting of polydatin, emodin, physcion and resveratrol, which were extracted by High-performance liquid chromatography (HPLC). The results showed that the drying kinetics was affected by the method and operation condition. Microwave drying was the fastest method. High temperature resulted in fast speed but low quality. Indicator compounds from samples of all the drying condition, were more than the samples of sun drying. Most polydatin and physcion was retained by microwave at 60?. Most emodin and resveratrol was retained by hot air at 80? and 60? respectively. Principal component analysis was used to comprehensively evaluate the compounds retained after these drying. Considering the time consumption, microwave drying at 60? was the most proper method. However, more research about the combining method of microwave drying and air drying should be studied.