Analysis of the Maca Metabolome by NMR to Detect Adulteration

Reviewed: Zhao J, Wang M, Khan IA. Detection of adulteration in dietary supplements: maca (Lepidium meyenii) case study by NMR approach. Poster presentation PG12 at: American Society of Pharmacognosy Annual Meeting; July 26, 2015; Copper Mountain, CO.

This poster presented an NMR-based approach to evaluate authentic maca (Lepidium meyenii, Brassicaceae) root, maca leaf, and 32 single-ingredient commercial maca products. The samples (200 mg) were extracted in 400 µL of deuterated methanol, sonicated, centrifuged, and the supernatant used for the NMR analysis. Metabolite profiles were submitted to statistical evaluation by principal component analysis (PCA), which was presented in a scatterplot of 31 authentic and 28 commercial samples. There was no clear clustering of authentic and commercial samples, indicating important differences in the chemical composition within samples of authentic maca and within the maca products. The authors used the presence of the signal at 4.32 ppm (using CD₃OD), characteristic of macamides, as an indicator of authentic maca. Based on the absence of this NMR signal in a number of samples, they concluded that some (the actual number is not specified in the poster) of the commercial products were adulterated.

Comment: The main advantages of this method, according to the authors, are the short sample preparation time and the lack of a need for commercial maca standard compounds. The metabolomics approach also allows analysts to look at all the methanol-soluble components in maca rather than focusing on one or two classes of compounds. Since the macamides are components that are characteristic for L. meyenii, they represent good marker compounds for authentication of whole, cut, or powdered maca hypocotyls. HPLC-UV-based methods to quantify macamides have been described earlier^1,2 and provide an alternative to the presented NMR study. However, the reliance on macamides to authenticate maca in commercial products, in particular for extracts made using an unknown manufacturing process, carries the risk that these products may be erroneously considered adulterated, since macamides are highly lipophilic and may not be present depending on the extraction process.

Anticipating that these preliminary results will be followed by a more in-depth publication, it will be interesting to see just how many samples were analyzed, what the extent of maca adulteration in the study is, and if the authors will be able to identify the adulterants in those products allegedly mislabeled as containing maca root as the single ingredient. 

References

1.     Ganzera M, Zhao J, Muhammad I, Khan IA. Chemical profiling and standardization of Lepidium meyenii (maca) by reversed phase high performance liquid chromatography. Chem Pharm Bull (Tokyo). 2002;50(7):988-991.

2.     McCollom MM, Villinski JR, McPhail KL, Craker LE, Gafner S. Analysis of macamides in samples of maca (Lepidium meyenii) by HPLC-UV-MS/MS. Phytochem Anal. 2005;16(6):463-469.