Effect of different drying methods on flavones content in pueraria

Objective: To explore the effect of different drying methods on the content of total flavones, puerarin, daidzin, daidzein, genistin and genistein in pueraria.Method: The pueraria root slices were dried by hot air, vacuum and freeze- drying.The content of total flavonoids in the dried pueraria root slices were investigated by spectrophotometer and puerarin, daidzin, daidzein, genistin, genistein in the dried pueraria root slices were determined by high performance liquid chromatography.The effect of different drying methods on the content of total flavones and the five flavones in the dried pueraria root were analyzed in order to select the best drying methond.Results: the total flavones content in pueraria root slices dried by freeze- drying was the highest and the total flavones content in pueraria root slices dried by hot air was the lowest, the total flavones content in pueraria root slices dried by vacuum and freeze-drying had no significant differences.In the pueraria root slices dryed by hot air, genistein was completely lost, the content of total flavones, puerarin, daidzein and genistin were decreased with the increase of drying temperatures, and that the content of daidzin was increased with the increase of drying temperatures.The content of daidzin and genistein in pueraria root slices dryed by hot air and vacuum showed significant differences, the content of daidzein and genistin had no significant differences.Conclusion: The low-temperature hot air drying method could be used to dry lower quality pueraria in order to decrease drying cost, the vacuum drying method could be used to dry higher quality pueraria, the freeze-drying method was very limited for improving pueraria quality.