Gas Chromatography–Mass Spectrometry-Based Classification of 12 Fennel (Foeniculum vulgare Miller) Varieties Based on Their Aroma Profiles and Estragole Levels as Analyzed Using Chemometric Tools

Fennel (Foeniculum vulgare Miller) is a popular aromatic plant native to the Mediterranean basin and cultivated worldwide that is valued for the nutritional and health benefits of its fruits. Headspace solid-phase microextraction of 12 fennel accessions of cultivated (F. vulgare subsp. vulgare) and wild forms (F. vulgare subsp. piperitum) of different origins was carried out for assessing their volatile distribution. Fifty-four volatiles were identified, with ethers amounting for the major class at ca. 52-99% attributed to the abundance of (E)-anethole and estragole. Several subsp. vulgare accessions proved to be excellent sources of the chief aroma (E)-anethole (95.9-98.4%), whereas high levels of estragole at ca. 72% were observed in subsp. piperitum from Minia and Khartoum and must be considered in the safety assessment of fennel. Other volatile classes were detected including ketones, esters, aldehydes, alcohols, and hydrocarbons (monoterpenes, sesquiterpenes, and diterpenes). Fenchone exceeded 15% of the total volatiles in some fennel specimens, linked to a conspicuous bitter aftertaste. The members of subsp. piperitum were more enriched in monoterpene hydrocarbons with sabinene found exclusively in these, while subsp. vulgare comprised a higher content of ethers. Principle component analysis determined isoterpinolene as a special component in subsp. piperitum. In all specimens from the same group, estragole was the most distinguished volatile compound according to the findings from orthogonal partial least squares-discriminant analysis. The highest estimated estragole levels were detected in subsp. piperitum from Minia at 89.8 mg/g. This comparative study provides the first comprehensive insight into volatile profiling of 12 fennel fruit varieties.