Authenticity Evaluation of Bulk Saw Palmetto Extracts by Isotopic Fingerprinting

Reviewed: Perini M, Paolini M, Pace R, Camin F. The use of stable isotope ratio to characterize saw palmetto (Serenoa repens). Food Chem. 2019;274:26-34.

Keywords: Adulteration, animal fats, GC-MS, isotopic fingerprinting, Serenoa repens, stable isotope ratio

The dilution or substitution of bulk ingredients labeled to be made from saw palmetto (Serenoa repens, Arecaceae) fruits with vegetable oils has been reported by a number of authors,¹ but the market presence of designer oils made from animal fats mimicking the fatty acid profile of authentic saw palmetto extracts has been discovered only recently.²

The same authors who initially reported on the issue with animal fats² have provided a more in-depth comparison of ²H/¹H, ¹³C/¹²C, and ¹⁸O/¹⁶O isotopic ratios in bulk saw palmetto, vegetable oils, and animal fats. In addition, these ratios were measured in a number of individual fatty acids from saw palmetto, vegetable oils, and animal fats. Variations in the isotopic ratios in plants and animals may have a number of reasons. For example, the ²H/¹H ratio in plants is influenced by the geographical origin of the local water. The ¹³C/¹²C ratio in plants depends on the type of photosynthesis that a plant is using. While most plants use exclusively the Calvin cycle, some plants (e.g., corn [Zea mays, Poaceae] or sugar cane [Saccharum officinarum, Poaceae]) have additional photosynthetic pathways, leading to a slightly higher ¹³C/¹²C ratio in the latter. The ¹³C/¹²C isotopic ratio of animal fats is known to be correlated with their diet, e.g., animals that feed exclusively on corn will have a higher ¹³C/¹²C ratio than those that ingest a wider variety of plants. The ¹⁸O/¹⁶O ratio depends on the temperature, freshwater input, and other climatic factors.

Isotope ratios were measured using gas chromatography with a split connector eluting the analytes into an isotope mass spectrometer and a single-quadrupole mass spectrometer. The latter was used to confirm the identity of the fatty acid. The results are expressed as the ratio difference (δ²H, δ¹³C, δ¹⁸O) of the material to be analyzed and a standard with a known isotopic ratio, e.g., the Vienna Standard Mean Ocean Water (VSMOW), which defines the ²H/¹H and ¹⁸O/¹⁶O composition of fresh water.

The isotopic ratios were determined in 20 authentic saw palmetto samples and nine bulk samples allegedly containing saw palmetto extract from suppliers in China. Average Isotopic ratios in authentic bulk saw palmetto varied between δ²H of -165 to -176‰, δ¹³C of -29.7 to -31.0‰, and δ¹⁸O of 27.2 to 40.7‰, respectively. In the commercial samples, values of δ²H of -197 to -231‰, δ¹³C of -27.5 to -29.4‰, and δ¹⁸O of 14.1 to 26.4‰, respectively, were measured. Similar variations in the isotopic ratios were seen when looking at the individual fatty acids.

The isotopic ratio values of the commercial extracts were not within the range for authentic saw palmetto extracts. Both bulk oil and all the individual fatty acids extracted from these samples showed a lower δ²H and δ¹⁸O than authentic saw palmetto samples, but also a lower ratio than most vegetable oils. Six of the commercial samples showed isotopic ratio patterns consistent with animal-derived fatty acids, while the remaining three had ratios that suggested a mixture of authentic saw palmetto extract with animal-derived fatty acids.

Comment: Reports of saw palmetto extract adulteration have mainly described dilution with undeclared vegetable oils, e.g., palm (Elaeis guineensis, Arecaceae), sunflower (Helianthus annuus, Asteraceae), or coconut (Cocos nucifera, Arecaceae) oil.¹ The appearance of materials labeled to contain saw palmetto extracts, which comply with the fatty acid profile of saw palmetto detailed, e.g., in the monograph of the United States Pharmacopeia,³ but have notable differences in the contents of fatty alcohols or sterols, has been documented more recently.⁴ However, many commercial saw palmetto extracts do not have specifications for fatty alcohols or sterols, and these compounds therefore may not be measured. Consequently, the designer extracts masquerading as authentic saw palmetto extracts may pass quality control tests despite being made with fatty acids from animal sources. The relatively simple tests for fatty alcohols and sterols may give a good indication if the material is authentic or not, and are good choices for those laboratories which do not want to spend the money on stable isotope measurements.

References

1. Gafner S, Baggett S. Adulteration of saw palmetto (Serenoa repens), revision 3. Botanical Adulterants Prevention Bulletin. Austin, TX: ABC-AHP-NCNPR Botanical Adulterants Prevention Program; 2018.
2. Perini M, Paolini M, Camin F, et al. Combined use of isotopic fingerprint and metabolomics analysis for the authentication of saw palmetto (Serenoa repens) extracts. Fitoterapia. 2018;127:15-19.
3. United States Pharmacopeial Convention. Saw Palmetto Extract. In: United States Pharmacopeia and National Formulary (USP 41-NF 36). Rockville, MD: United States Pharmacopeial Convention. 2018.
4. Gafner S. Evidence for Adulteration of Saw Palmetto Extracts. Botanical Adulterants Monitor. 2017;11.