Not a load of rhubarb: Study finds 16 chemicals that emerge from processing rhubarb

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  • Published: Aug 1, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Laboratory Informatics / Chemometrics & Informatics
thumbnail image: Not a load of rhubarb: Study finds 16 chemicals that emerge from processing rhubarb


Chinese physicians of bygone generations prescribed natural remedies for a multitude of ailments and maladies. Today, practitioners of Traditional Chinese Medicine are retracing their steps with modern analytical techniques in an attempt to elucidate the active components behind their therapeutic activity.

We are all familiar with this. We reel off a list of ailments and maladies to our physician as long as our arms – fatiguing fever, that tickly cough that won’t budge and insomnia. These ailments have afflicted humankind since the dawn of the agricultural revolution and beyond. Whilst today’s doctors can call on a whole cornucopia of meticulously formulated pharmaceuticals, practitioners of Traditional Chinese Medicine (TCM for short) have turned to nature for over two millennia.

Constipated? Succumbed to an infection? Perhaps some rhubarb would help. This sour herb of the Rheum genus, according to TCM experts, is a potent laxative amongst other medical traits, such as anti-bacterial. Processing – whether by washing, cutting, soaking, boiling, frying, roasting or steaming – is an integral tenet of TCM. This processing, TCM experts claim, enhances the efficacy and spectrum of uses of herbs, whilst minimising their toxicity. And rhubarb is no different.

Rhubarb is often administered in its ‘prepared’ form. For this, rhubarb is steamed with glutinous rice wine until it is charcoal black, inside and out. ‘Prepared rhubarb shows quite a different curative effect from raw rhubarb,’ Zhu and colleagues at the University of Chinese Medicine, Nanjing, wrote in their paper published in the Journal of Separation Science. ‘This change of curative effects surely would be related to the inside chemical materials basis change during the processing.’

Bespoke database

The researchers based in China set out to identify the exact chemicals this transmutation brings about, using both high-resolution UPHLC-MS and a bespoke identification database. For this, they profiled nine batches of raw rhubarb and nine batches of prepared rhubarb procured from the major rhubarb-producing regions of China. Rhubarb was first filtered and cleansed of impurities with an RP-C18 SPE column. Next, rhubarb components were loaded onto a UHPLC-C18 column and resolved over a 32-minute slightly acidified aqueous to MeOH gradient. Detection was done online with a Q-TOF MS operated in both positive and negative ionisation modes, after which the most abundant ions were fragmented with 30 V of collisional energy, yielding the all-important, information-rich MS/MS spectra. To aide their identification of rhubarb components, the authors also created a bespoke database of Rheum components by scouring the literature and existing open-access databases for pertinent identifiers – chemical structures and molecular formulas and weights, for example – to which their MS/MS data could be compared.

16 peaks

MS/MS spectra yielded 63 peaks associated with raw rhubarb and 54 peaks with prepared rhubarb. From these, 45 chemical compounds were matched within an error of 10 ppm to entries in their bespoke database. After crunching the data, 16 peaks were what distinguished the purported clinically active rhubarb from its non-processed equivalent. Of these, 15 were mostly anthraquinonoid glycosides found at lower quantities post-processing, whilst one – rhein – was more abundant. Could rhein be the all-elusive, active chemical? In all, their method identified 10 novel compounds not previously associated with processed rhubarb. ‘The method developed,’ the authors conclude, ‘demonstrated a convenient and reliable way to clarify the differences in decoction after herbal drug processing.’

Related Links

J. Sep. Sci. 2016, Early View article,. Zhu et al. Profiling and analysis of multiple compounds in rhubarb decoction after processing by wine steaming using UHPLC–Q-TOF-MS coupled with multiple statistical strategies.

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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