Croatian sea fennel may contain a treasure trove of preservative and anti-aging metabolites

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Feb 26 2024

In a recent study published in the journal Foods, researchers evaluated the biological activity of hydrolats and essential oils derived from French and Croatian sea fennel. Despite being the main by-product obtained from the isolation of essential oils from these plants, research into the biochemical properties of fennel-derived volatiles remains lacking. Combinations of hydrodistillation, chemical analysis, and biological activity analysis revealed that the chemistry of the two sea fennel populations under study differed significantly in both composition and biological function. The Croatian sea fennel particularly displays beneficial anti-collagenase and anti-tyrosinase activity, highlighting its anti-aging potential and cosmetic application.

Study: Volatiles from French and Croatian Sea Fennel Ecotypes: Chemical Profiles and the Antioxidant, Antimicrobial and Antiageing Activity of Essential Oils and Hydrolates. Image Credit: Happy window / Shutterstock

What is sea fennel?

Sea fennel is a common name that refers to a group of perennial aromatic herbs belonging to the carrot (Apiaceae) family. They can be found growing on beaches, rocks, breakwaters, and piers around the world. Sea fennels are halophytic plants rich in nutritional and organoleptic compounds. Given the increasing global consumer demand for the use of safe and natural ingredients in cosmetics, pharmaceuticals, and other essential oil (EO)-using products, research has extensively explored the biological applications of fennel-derived EOs.

Unfortunately, the potential benefits of volatiles obtained during the isolation of EOs from the fennel plant remain unstudied. Often termed 'hydrolats,' research conducted on these volatiles from other herb sources reveals that they present numerous benefits over EOs, including potent bioactive functions and reduced dosage-dependent cytotoxicity. Additionally, despite being traditionally used in perfume and cosmetic manufacture, sea fennels remain understudies for their clinical and nutraceutical potential. Limited information on EO compositions from different regions suggests that they may not all be the same, with concentrations of metabolites, especially dillapiole.

Understanding the geographical variability in sea fennel biochemical profiles and the potential of both their EOs and volatiles in biological, cosmetic, and pharmaceutical industries would allow for the sustainable and eco-friendly use of safe and naturally derived products, often considered waste (hydrolats). These findings may further guide future research on these abundant and near-ubiquitous yet poorly understood plants.

About the study

In the present study, researchers used a combination of chemical and biological analyses to investigate the biochemical composition and biological properties of sea fennel derived from French and Croatian regions. The study samples comprised 2 kg of sea fennel aerial parts collected from Dalmatia (Mediterranean ecotype) and the Brittany shoreline (Atlantic ecotype) in October 2022. Hydrodistillation was used for EO extraction, with extracted EOs dried using sodium sulfate (Na₂SO₄).

Volatiles from hydrolats were extracted using headspace solid-phase microextraction (HS-SPME), following which gas chromatography-mass spectrometry (GC-MS) was used for chemical composition analysis. The antioxidant activity of EOs and volatiles was estimated using a microplate spectrometric reader. Reduction ability was tested using a Ferric Reducing Antioxidant Power (FRAP) assay. Biological assays further included the synthetic stable 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), the nitric oxide radical (NO), and the hydroperoxyl radical (HOO) assays.

The antimicrobial activities of fennel-derived samples were computed using Staphylococcus aureus ATCC 33862 (gram-positive) Escherichia coli ATCC 1053, and Pseudomonas aeruginosa ATCC 27853 (gram-negative) bacterial strains. Mushroom tyrosinase with L-tyrosine as substrate was used to evaluate anti-tyrosinase activity, elastase from porcine pancreas Type IV E0258 with N-Succinyl-Ala-Ala-Ala-p-nitroanilide (SANA) as substrate evaluated anti-elastase activity, and the Enzo Life Sciences MMP-1 kit for anti-collagenase activity. The Tukey post hoc test was used for statistical comparisons between cohorts.

Study findings

French sea fennel EO extracts were found to be slightly more chemically diverse than their Croatian counterparts, having 13 components in place of the latter's 12. Dillapiole, carvacryl methyl ether, and γ-terpinene were found to be the main bioactive components of French sea fennel EOs, while Croatian sea fennel EOs were found rich in sabinene and limonene, highlighting that these populations are unique chemotypes.  

"It is hard to draw general conclusions about the causes of the differences in the chemical composition of sea fennel EOs, as they may be due to the different abiotic and biotic factors that affect the synthesis and accumulation of plant secondary metabolites, such as the harvest location or geographical variations, plant vegetation/harvest period/growth cycle, plant part used, climatological factors, soil abiotic factors, etc. However, our results agreed with the conclusions of other authors, according to which the main reason is simply the existence of different plant chemotypes (intraspecific variability)."

The complexity of French sea fennel extends to their volatiles, with these plants containing 32 identifiable compounds to Croatian sea fennel's 17. Dillapiole, thymol methyl ether, and γ-terpinene were found in the highest concentration in French sea fennel volatiles, while the Croatian samples were observed to contain terpinene-4-ol and 10-(acetyl methyl)-3-care.

Antioxidant tests revealed that sea fennel-derived compounds' antioxidant potential pales compared to gallic acid, the gold standard in natural phenolic antioxidants. FRAP test values were found to vary between 0.77 and 1.34 µM Fe2+/L, with similar observations made in DPPH assays. Reducing potential analyses paint a different picture, with both French and Croatian sea fennels displaying reducing potential, slightly higher in the latter. Surprisingly, the potency of volatiles and hydrolats was found to be more than three-fold higher than a corresponding amount of EO, highlighting their future industrial potential.

The observable advantages of volatiles over EOs were also observed in the radical scavenging efficiencies of the two cohorts, with volatiles being 3.8 times more efficient than their EO counterparts.

"French EO showed no antimicrobial activity against Escherichia coli and Pseudomonas aeruginosa, but a slight activity against Staphylococcus aureus (8 mm). Conversely, the Croatian EO moderately inhibited the growth of P. aeruginosa (8 mm), but strongly inhibited that of the other two bacterial strains (18 and 25 mm for E. coli and S. aureus, respectively). Interestingly, the CRO EO's inhibition of the latter bacterial strain was as strong as that of the commonly used bactericidal streptomycin. Furthermore, neither the French nor the Croatian hydrolates showed any antimicrobial effect."

Importantly, Croatian sea fennel was observed to display anti-tyrosinase and anti-collagenase activity, both of which were absent in French sea fennel. This highlights Croatian sea fennel as the target of future bioprospecting studies to discover safe and natural anti-aging cosmetic additives.