Objective

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To compare the four preparation methods of Rehmanniae Radix juice described in ancient literature and find the method that is most suitable for the preparation of Rehmanniae Radix juice used in Baihe Dihuangtang.

Method

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The ancient medical books record four methods for preparing Rehmanniae Radix juice： crushing fresh Rehmanniae Radix for juice， steaming fresh Rehmanniae Radix for juice， boiling fresh Rehmanniae Radix for juice， and boiling dry Rehmanniae Radix for juice. Ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry （UPLC-Q-TOF-MS） was employed to detect the compounds in the four juice samples， followed by principal component analysis （PCA）.

Result

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① Totally 27 compounds were identified in the juice samples， including 10 iridoid glycosides， 14 phenylethanoid glycosides， 2 phenolic acids， and 1 irisone. Among them， 15 common compounds were shared by the four juice samples， including 7 iridoid glycosides， 7 phenylethanoid glycosides， and 1 phenolic acid. ② Five common compounds in the four juice samples can be matched with the reference standards， which were catalpol， aucubin， rehmannioside D， ajugol， and purpureaside C. ③ Verbascoside and isoacteoside were not detected in the juice prepared by crushing fresh Rehmanniae Radix， while it was detected in the other three juice samples， which indicated that the two components were produced after heating rather than being the original components in fresh Rehmanniae Radix. ④ The comparison of the ion fragments demonstrated that verbascoside was produced from purpureaside C after the cleavage of the glycosidic bond and removal of a molecule of mannose. ⑤ Isoacteoside could be isomerized from verbascoside， and its relative content increased with the extension of heating time. However， the relative content of verbascoside and purpureaside C did not decrease significantly. Therefore， it was hypothesized that purpureaside C was produced from its upstream component.

Conclusion

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The juice prepared by crushing fresh Rehmanniae Radix has the chemical composition significantly different from the juice samples prepared with the other 3 methods， while the latter 3 juice samples had similar chemical composition. Although all the four methods can be used， it is more suitable to prepare Rehmanniae Radix juice by steaming fresh Rehmanniae Radix， boiling fresh Rehmanniae Radix， and boiling dry Rehmanniae Radix.