NMR Analysis of Commercial Passionflower Herb Extracts Sold on the Brazilian Market

Reviewed: Flores IS, Martinelli BCB, Lião LM. High-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) as a tool in the determination of biomarkers of Passiflora-based herbal medicines. Fitoterapia. 2020;142:104500.

Keywords: Adulteration, NMR, passionflower, Passiflora incarnata

The herb of passionflower (Passiflora incarnata, Passifloraceae) is a widely used ingredient in herbal teas and dietary supplements to help in situations of stress and to promote restful sleep. Several additional Passiflora species are found in commerce and have data suggesting some level of pharmacological equivalence. In Brazil, the most common medicinal passionflower species are P. alata, P. edulis, and P. incarnata. The American Herbal Products Association’s Herbs of Commerce. 2nd ed.,¹ includes P. caerulea, P. coriacea, P. edulis, P. foetida, P. incarnata, P. laurifolia, and P. quadrangularis, although only P. incarnata can be sold under the standard common name of passionflower.

The proton nuclear magnetic resonance (¹H NMR) spectra of seven commercial products labeled to contain P. incarnata (n = 6) or P. alata (n = 1) extract were compared to an extract of authentic P. alata made using deuterated methanol. The commercial products contained passionflower extract alone (n = 3), or in combination with hawthorn (Crataegus oxyacantha, Rosaceae, plant part not specified) and other herbal extracts (n = 4).

Proton NMR signals for seven flavonoids (hispidulin, isoorientin, isovitexin, luteolin, luteolin-7-O-glucoside, orientin, and vitexin) were identified in the authentic reference material. However, only the three commercial single-ingredient products showed signals for flavonoids. In addition to hispidulin, isovitexin/vitexin, and orientin, these three products also contained kaempferol and quercetin. Two of the combination products had an almost identical ¹H NMR fingerprint, dominated by salicin. These two products were labeled to contain willow (Salix alba, Salicaceae) bark extract in addition to hawthorn and passionflower extracts. However, none of the characteristic signals for passionflower flavonoids were observed. The remaining two combination products did not provide any distinctive ¹H NMR signals in the range for aromatic protons, and thus were considered to contain neglectable amounts, if any, of passionflower extract.

Comment: Data on the composition of commercial passionflower herb extracts are relatively rare. Avula et al.² analyzed four commercial dietary supplements purchased online in the USA and found that three matched the flavonoid pattern found in passionflower, while one extract did not contain any flavonoids. Ramirez-Durón et al.³ evaluated eight commercial passionflower products purchased in Nuevo León, Mexico. None of these products matched the thin-layer chromatography (TLC) profile of authentic P. incarnata. However, there are several species of Passiflora used in Mexico for medicinal purpose. The present study also suggests that there are quality issues with commercial passionflower extracts, since four of the seven products tested did not contain any of the flavonoids typically associated with passionflower. One of the shortcomings of this paper is the lack of authenticated P. incarnata leaf material for comparison with the commercial products. Since the flavonoid composition of passionflower herb is reportedly variable, more data on the chemical composition of passionflower leaves from different regions around the globe are needed.

Of interest is the occurrence of kaempferol and quercetin in the three single-ingredient products. Passionflower is known to have predominantly apigenin- and luteolin-glycosides, e.g., isoorientin and isovitexin. While kaempferol and quercetin have been reported from passionflower,^4,5 these reports need confirmation from additional studies using more sophisticated methods of identification.

References

1. McGuffin M, Kartesz JT, Leung AY, Tucker AO. American Herbal Products Association’s Herbs of Commerce. 2nd ed. Silver Spring, MD: American Herbal Products Association; 2000.
   
2. Avula B, Wang YH, Rumalla CS, Smillie TJ, Khan IA. Simultaneous determination of alkaloids and flavonoids from and flavonoids from aerial parts of Passiflora species and dietary supplements using UPLC-UV-MS and HPTLC. Nat Prod Rep. 2012;7(9):1177-1180.
   
3. Ramirez-Durón R, Ceniceros-Almaguer L, Salazar-Aranda R, Salazar-Cavazos M, Waksman de Torres N. Evaluation of thin-layer chromatography methods for quality control of commercial products containing Aesculus hippocastanum, Turnera diffusa, Matricaria recutita, Passiflora incarnata, and Tilia occidentalis. J AOAC Int. 2007;90(4):920-924.
   
4. Gavasheli NM, Moniavo II, Éristavi LI. Flavonoids from Passiflora incarnata. Khim Prirodn Soed. 1974;1:95-96. 
   
5. Guseinov MD, Bobkova NV, Svistunov AA, Tarasov VV, Bokov DO, Sergunova EV, Kovaleva TY. Flavonoids in Passiflora incarnata L. dry extract of Russian origin. Pharmacogn J. 2019;11(5):1143-1147.