Comparative Evaluation of the Volatile Profile of the Essential Oil, the Hydrolate and the Plant Material from Origanum vulgare subsp. virens Grown in Portugal

Oregano (Origanum vulgare L.) is one of the most important aromatic plants in the world, recognized for its applications in food and traditional medicine, as well as for its biological potential and chemical diversity. This study investigated the chemical diversity of 12 accessions of Origanum vulgare subsp. virens from Portugal, grown in the wild and on an experimental field (EF), through a comparative analysis of their essential oils, hydrolate volatiles, and the volatiles obtained by headspace solid-phase microextraction (HS-SPME). The compounds were identified by gas chromatography coupled with mass spectrometry and quantified by gas chromatography with a flame ionization detector. The yields of the essential oil ranged from 1.5 to 3.3% (v/w). A total of 70 compounds were identified in the essential oil, 74 compounds in the hydrolate volatiles, and 48 compounds by HS-SPME. Cluster analysis separated the 36 samples into two main groups, corresponding to the linalool (35–77%) and the terpene-phenolic chemotypes [thymol (24–82%) and carvacrol (18–93%)]. PCA clearly separated the three methodologies of volatiles extraction while keeping similar chemotypes. With few exceptions, the wild and the corresponding EF-grown plants provided comparable volatile profiles. The choice of analytical method can influence the chemical profile, which demonstrates the need for a more comprehensive approach to understanding the chemical descriptors from Portuguese oregano.