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The use of naturally derived compounds to maintain or improve well-being or enhance particular bodily functions is becoming increasingly common. Such compounds, which are frequently plant extracts, are referred to as nutraceuticals and are widely used in naturopathic, homeopathic and traditional medicines. They encompass vitamins, minerals, supplements, probiotics and herbal remedies. Stephen De Felice, who coined the term 'nutraceutical', gave the definition as a "food, or parts of a food, that provide medical or health benefits, including the prevention and treatment of disease".
Nutraceuticals are promoted by the companies producing them as having a range of positive health effects, including healing, rejuvenation, protection against chronic illness, and augmentation of the structure or function of the body. The popularity of these natural health products is reflected in the fact that the global market for herbal remedies alone is estimated to be $83 billion1.
Despite such widespread usage, the marketing of nutraceuticals is subject to considerably lower levels of regulations than pharmaceuticals. This lack of regulation means that claims of effectiveness are not substantiated and the safety of taking these products is frequently unknown. Furthermore, the content of many marketed nutraceuticals has not been verified2,3,4 and unscrupulous companies market products containing little active ingredient, using instead cheaper low quality or ineffective alternatives.
Authentication of nutraceuticals
The majority of nutraceutical authentication is conducted using targeted analysis with mass spectroscopy and molecular spectroscopy. Such analyses require identification and quantification of each metabolite in the sample. This can be complicated and time-consuming since the spectra are often complex and it is not easy to select and quantify individual peaks.
Untargeted analysis achieved using chemical profiling or spectral fingerprinting can be conducted more rapidly, as individual components of the botanical sample are not identified or quantified5,6. Instead, the spectra are compared point by point using known compounds, chemometric classifiers, for comparison.
With the global nutraceutical market continuing to grow rapidly, regulations for the analysis of nutraceuticals are being introduced to ensure the quality of such products and protect consumer safety. Consequently, there is increasing demand for rapid but effective methods for the analysis of complex natural products.
A key consideration when undertaking classification by chemical profiling is reproducibility of the spectra. Consequently, although it is not as sensitive as mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy is increasingly becoming the technique of choice for chemical profiling of plant extracts since it provides more reproducible results7.8.
Nuclear magnetic resonance spectroscopy in chemical profiling
In order to interpret spectra obtained by NMR, it is necessary to know how much light is emitted at each wavelength in the light source. This is typically achieved using a Fourier Transform, which converts the light characteristics into the frequency domain so spectra can be visualized. The real absorbance spectrum achieved in this way has sharp and symmetric peaks, which are needed for qualitative analysis or quantitative analysis. However, the use of such methodology results in about half of the available information being discarded.
Reproducibility is the key factor for accurate chemical profiling, and the appearance of the peaks is not a major concern. Consequently, it is beneficial to sacrifice some resolution in order to maximize reproducibility. Using this logic, the magnitude or amplitude spectrum, which includes data from the entire NMR signal, has recently been investigated as a tool in the authentication of nutraceuticals. In this technique, the increase in the signal results from the greater peak areas of the wider peaks than those found in the real spectrum. It does not produce a spectrum as clear as the real absorbance spectrum, but it benefits from having a greater signal-to-noise ratio and inherent reproducibility. It is also easy to interpret since the magnitude of the peaks relates directly to the signal.
This technique was used to obtain spectra from tea extracts, liquor samples, hops extracts, and cannabis extracts9. Samples across the four datasets were evaluated against six classifier compounds using proton NMR measurements made using a Bruker Avance III HD and Bruker Ascend™ 500 nuclear magnetic resonance spectrometer (Bruker BioSpin AG, Fällanden, Switzerland) equipped with a Ø5-mm broad-band multinuclear probe.
For 23 of the 24 classifier comparisons, the absolute magnitude spectral dataset gave significantly improved results for all classifiers compared with the real spectrum. Error scaling resulted in appropriate weights being given to the smaller peaks in the spectra and the absolute magnitude spectral scores allowed much greater resolution of samples than the real spectral scores9.
Absolute magnitude NMR provides a powerful tool for the chemical profiling of complex materials.
- WHO. The World Medicines Situation 2011—Traditional Medicines: Global Situation, Issues and Challenges [Internet]. WHO Press, Geneva, Switzerland; 2011. Available at: http://digicollection.org/hss/en/m/abstract/Js18063en/
- Remsberg CM, Good RL, Davies NM. Ingredient Consistency of Commercially Available Polyphenol and Tocopherol Nutraceuticals. Pharmaceutics. 2010;2(1):50-60. doi:10.3390/pharmaceutics2010050.
- Draves A.H., Walker S.E. Analysis of the hypericin and pseudohypericin content of commercially available St John's Wort preparations. Can. J. Clin. Pharmacol. 2003;10:114–118.
- Russell A.S., Aghazadeh-Habashi A., Jamali F. Active ingredient consistency of commercially available glucosamine sulfate products. J. Rheumatol. 2002;29:2407–2409.
- Harnly J, Chen P, Harrington PD. Probability of identification:adulteration of American ginseng with Asian ginseng. J AOACInt. 2013;96(6):1258–1265.
- Chen P, Harnly JM, Harrington PD. Flow injection mass spectroscopic fingerprinting and multivariate analysis for differentiation of three Panax species. J AOAC Int. 2011;94(1):90–99.
- Mahrous EA, Farag MA. Two dimensional NMR spectroscopic approaches for exploring plant metabolome: a review. J Adv Res.2015;6(1):3–15.
- Larive CK, Barding GA, Dinges MM. NMR spectroscopy for metabolomics and metabolic profiling. Anal Chem. 2015;87(1):133–146.
- De B Harrington P, Wang X. Spectral Representation of Proton NMR Spectroscopy for the Pattern Recognition of Complex Materials. J Anal. Test 2017. Epub ahead of print April 2017. Available at http://link.springer.com/article/10.1007/s41664-017-0003-y
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