Metabolomic Profiling of Saw Palmetto Extracts Allows Distinguishing among Materials Produced Using Different Extraction Methods and to Detect Adulteration with Other Vegetable Oils

Reviewed: Booker A, Suter A, Krnjic A, et al. A phytochemical comparison of saw palmetto products using gas chromatography and ¹H nuclear magnetic resonance spectroscopy metabolomic profiling. J Pharm Pharmacol. 2014;66(6):811-822.

This is another example of collaboration between a dietary supplement manufacturer (Bioforce AG; Roggwil, Switzerland) and an academic institution (University of London; London, UK). The research team analyzed 57 commercial samples (soft gel or hard gel capsules, tablets, or tinctures) obtained from retail outlets or pharmacies from nine countries in Asia, Europe, and North America. Of these products, 29 contained only saw palmetto (Serenoa repens syn. Sabal serrulata, Arecaceae), while the other 28 were labelled as saw palmetto combined with other constituents such as vitamins, herbal extracts, or minerals. Nine fatty acids were quantified in 46 products using an established gas chromatography-flame ionization detector (GC-FID) method. The metabolomic profiles (metabolomics is the term used for the study of unique chemical fingerprints produced by cellular processes, such as those seen in plants) of 34 saw palmetto extracts were recorded using ¹H NMR spectroscopy, and analyzed statistically by principal component analysis (PCA).

According to the results from the GC-FID analysis, the fatty acid composition of the majority of the saw palmetto mono-preparations was comparable, while products containing additional ingredients were predictably much more heterogeneous. The actual contents of fatty acids in the mono-preparations varied between 0.1 and 4.6 times the levels indicated on the label. As expected, products containing saw palmetto and additional vegetable oils showed a different fatty acid composition from the 29 mono-preparations.

In one of the products labeled to contain additional ingredients, ¹H NMR spectroscopy analysis was able to confirm the identity of the added ingredients as soy (Glycine max, Fabaceae) bean oil and glycerin. The analysis by ¹H NMR spectroscopy also allowed looking at a wider range of chemical compounds (for example, β-sitosterol, γ-tocopherol and δ-tocopherols, or β-carotene) and comparing each of the products based on their total extractable metabolite content. The metabolic pattern found in ethanolic preparations showed that the majority of the extract manufacturers used the same mixture of immature and mature fruits obtained from a variety of harvesting regions in Florida. The authors conclude that both methods provide valuable information, and suggest that PCA-based models for saw palmetto products could be used in product development and quality control, in particular for the detection of adulterated material.

Comment: Substitution or thinning of saw palmetto berry extract with other vegetable oils is unfortunately documented as being relatively common, especially in years where saw palmetto harvests are not robust enough to meet market demands. A story published in “Natural Products Insider” in 2009 revealed that palm, canola (Brassica napus, Brassicaceae), olive (Olea europaea, Oleaceae), and coconut (Cocos nucifera, Arecaceae) oils have been found as adulterants, and that the occurrence tends to escalate after a supply shortage.¹ The rather comprehensive overview on the situation in the marketplace by Booker et al. seems to indicate a possible improvement of the situation, since all 57 commercial products actually contained saw palmetto and the presence of additional vegetable oils was declared on the labels. There are a number of methods (e.g., in the monographs in the European Pharmacopoeia, the United States Pharmacopeia, or by AOAC International)^2-4 to authenticate saw palmetto extracts but detection of adulteration in products where saw palmetto is mixed with other vegetable oils is still challenging. Using an analytical fingerprinting technique like GC-FID or ¹H NMR combined with an appropriate statistical analysis is a good way to ensure that the ingredient has the required composition.

References

1.    Myers S. Saw palmetto quality issues. Natural Products Insider. September 11, 2009. Available at: http://www.naturalproductsinsider.com/articles/2009/09/saw-palmetto-quality-issues.aspx. Accessed October 29, 2014.

2.    European Directorate for the Quality of Medicines & Healthcare. European Pharmacopoeia (EP 7.4). Strasbourg, France: Council of Europe; 2011.

3.    United States Pharmacopeial Convention. Saw palmetto. In: USP 37-NF 32. Rockville, MD: United States Pharmacopeial Convention; 2014.

4.    Sorenson WR, Sullivan D. Determination of campesterol, stigmasterol, and beta-sitosterol in saw palmetto raw materials and dietary supplements by gas chromatography: single-laboratory validation. J AOAC Int. 2006;89(1):22-34.