Gas Chromatography–Mass Spectrometry Analysis of Volatile Organic Compounds from Three Endemic Iris Taxa: Headspace Solid-Phase Microextraction vs. Hydrodistillation

<i>Iris</i> taxa are sources of valuable essential oils obtained from aged rhizomes used by various industries, including pharmacy, cosmetic, perfume, and food industry, in which irones are the most important aroma components. In this study, volatile organic compounds (VOCs) obtained from dried rhizomes of three endemics from Croatia, <i>Iris pseudopallida</i>, <i>I. illyrica</i>, and <i>I. adriatica</i>, were studied. The VOCs were isolated by three different methods: headspace solid-phase microextraction (HS-SPME) using divinylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) fiber or polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber, and hydrodistillation (HD). The samples were analyzed by gas chromatography-mass spectrometry (GC-MS). In five out of six samples, the main compounds detected by HS-SPME were perilla aldehyde, butan-2,3-diol, acetic acid, 2-phenylethanol, benzyl alcohol, hexanal, and nonanal, while 6-methylhept-5-en-2-one, <i>trans</i>-caryophyllene, and ethanol were common for all studied samples. The former VOCs were absent from the oldest, irone-rich <i>I. pseudopallida</i> sample, mainly characterized by <i>cis</i>-α-irone (43.74-45.76%). When using HD, its content was reduced (24.70%), while docosane prevailed (45.79%). HD yielded predominantly fatty acids, including myristic, common for all studied taxa (4.20-97.01%), and linoleic (40.69%) and palmitic (35.48%) as the major VOCs of <i>I. adriatica</i> EO. The performed GC-MS analyses of EOs, in combination with HS-SPME/GC-MS, proved to be useful for gaining a better insight into <i>Iris</i> VOCs.