Focus on Proanthocyanidins

Adulteration of Grape Seed Extracts

Reviewed: Villani TS, Reichert W, Ferruzzi MG, Pasinetti GM, Simon JE, Wu Q. Chemical investigation of commercial grape seed derived products to assess quality and detect adulteration. Food Chem. 2015;170:271-280.

Grape (Vitis vinifera, Vitaceae) seed extract (GSE) is becoming increasingly popular as a dietary supplement ingredient due to the high content in polyphenolic antioxidants at a relatively affordable price, since this ingredient is mainly produced as a byproduct of the winemaking industry. The main polyphenols are flavan-3-ol monomers and polymers. The polymers are known as proanthocyanidins (PACs); the term oligomeric proanthocyanidin (OPC) is not well defined in the sense that the number of monomer units in an oligomer varies among authors, but most often it is limited to a maximum of 10 units. Oligomeric and polymeric proanthocyanidins are also known as condensed tannins.

Two distinct classes of PACs can be defined based on chemical structure, known as A-type and B-type PACs. A-type PACs are linked by a C-C bond, usually between C-4β and C-8 (sometimes between C-4β and C-6), and an ether bridge between the two flavan-3-ol monomer units, whereas the B-type PACs linked only by the C-C bond (Figure 1). GSE reportedly contains only B-type PACs, which can be used as a criterion to detect adulteration with PACs from other sources that contain both types of polymers.

          

A-type proanthocyanidin: procyanidin A2	B-type proanthocyanidin: procyanidin B1

Figure 1: Chemical structures of A- and B-type proanthocyanidins

The authors have used both HPLC-UV/MS and HPTLC to analyze the PACs in authentic grape seed, pine (Pinus spp., Pinaceae) bark, and peanut (Arachis hypogaea, Fabaceae) skin extracts, and in 21 commercial GSE products that were obtained from a variety of sources, including dietary supplement retailers, supermarkets, and online vendors. While both analytical approaches allowed the distinction between grape seed and peanut skin extracts, GSE and pine bark extract were found to have a remarkably similar qualitative profile of PAC monomers and dimers. High-quality GSEs were found to contain larger amounts of PACs than pine bark extracts, but neither HPLC-UV/MS nor HPTLC were able to conclusively distinguish low-quality GSEs and pine bark extracts. Overall, in six of the commercial samples, grape seed was considered to be substituted with peanut skin extract, while an additional three samples showed evidence of admixture of an ingredient containing A-type PACs. Based on the authors’ evaluation, the adulterant again is likely to be peanut skin extract.

Comment: Results similar to the reviewed study were presented at the American Herbal Products Association’s 2014 Botanical Congress by Sudberg et al.¹ The adulteration of grape seed extracts with peanut skin extracts has the potential to be very damaging for the dietary supplement industry. The US federal Food Allergen Labeling and Consumer Protection Act requires that all packaged food products sold in the United States that contain peanuts as an ingredient must list the word “peanut” on the label. The consumer is not only deceived by buying a product that is not what it is purported to be, but due to the allergenic potential of peanuts in general (even if the allergenicity of processed peanut skins is lower than that for peanuts themselves^2,3) it also represents a safety risk. In the United States alone, the prevalence of people sensitive to peanuts or tree nuts was estimated to be 1.4% in 2008.⁴ The self-determined prevalence of peanut allergies worldwide ranges from 0% in 18 month old children from Iceland to 15% for a group of 15-17-year-olds from France.⁵

One shortcoming of the publication is that it is unclear how the peanut skin and pine bark materials were authenticated. In addition, the exact Pinus species (the actual species used was Masson pine [Pinus massoniana], as specified by Qingli Wu in an e-mail on January 7, 2015) should have been indicated in the paper, since the PAC composition may vary significantly from one species to another. Nevertheless, the available TLC and HPTLC methods provide an affordable and reliable tool to detect adulteration of GSE with peanut skin extract. The HPLC-UV/MS instrument used by Villani et al. is more expensive than TLC or HPTLC equipment, but its use would provide some additional information with regard to the identity of the adulterant. Based on the underlying chemistry, it should be obvious that the UV/Vis methods often used to specify total phenolics (e.g., Folin-Ciocalteu, vanillin/HCl, or dimethylaminocinnamaldehyde [DMAC] assays) will be easily fooled by the addition or substitution of other PAC-containing extracts and are inadequate to determine the identity of GSE.

References

1.     Sudberg E, Sudberg S, Nguyen J. Validation of a high performance thin-layer chromatographic fingerprint method for the simultaneous identification of grape seed and peanut skin and the adulteration of commercial grape seed extract with peanut skin. AHPA Botanical Congress, Las Vegas, NV. October 10, 2014.

2.     Constanza KE, White BL, Davis JP, Sanders TH, Dean LL. Value-added processing of peanut skins: antioxidant capacity, total phenolics, and procyanidin content of spray-dried extracts. J Agric Food Chem. 2012;60(43):10776-10783.

3.     Nordlee JA, Taylor SL, Jones RT, Yunginger JW. Allergenicity of various peanut products as determined by RAST inhibition. J Allergy Clin Immunol. 1981;68(5):376-382.

4.     Sicherer SH, Muñoz-Furlong A, Godbold JH, Sampson HA. US prevalence of self-reported peanut, tree nut, and sesame allergy: 11-year follow-up. J Allerg Clin Immunol. 2010;125(6):1322-1326.

5.     University of Portsmouth; Literature searches and reviews related to the prevalence of food allergy in Europe. EFSA supporting publication 2013:EN-506. Available at http://www.efsa.europa.eu/en/search/doc/506e.pdf. Accessed December 10, 2014.