Variation in essential oil content and composition of Ridolfia segetum Moris based on 30-hour prolonged fractionated extraction procedure

Abstract A comprehensive study on essential oil samples extracted from Ridolfia segetum Moris (Apiaceae) collected in Tarquinia (Italy) is reported. In this study, a 30-hour, fractionated, steam distillation procedure for essential oil preparation was applied. The gas chromatographic-mass spectrometry analysis showed monoterpene o-cymene and phenylpropanoid dill-apiol as the major essential oil’s constituents revealing a new chemotype dependent on extraction duration. Great impact of the duration of the distillation process on chemical profile of essential oil was observed; prolonged distillation gives chemically more diverse essential oil samples. Preliminary microbiological evaluations of the essential oils samples revealed some activity, although not high, against Candida albicans. Graphical Abstract


Introduction
Many essential oils (EOs) and their ingredients have an unexpectedly large range of applications. They are mainly obtained by hydro-and/or steam distillation apparatus in 2-4 (exceptionally 5) h. Recently, the 24-hour steam distillation procedure for EO preparation, in terms of different harvesting and extraction times, was applied on different plant species (Bo zovi c et al. 2017a(Bo zovi c et al. , 2017b(Bo zovi c et al. , 2018Garzoli et al. 2018aGarzoli et al. , 2018b. The procedure revealed that shortening or extending the extraction time, a different chemical composition profile of the oil could be obtained with variation in the related biological activity. In line with those studies, dried Ridolfia segetum Moris (RS) material, collected in Tarquinia countryside (Viterbo, Italy), was fractionally extracted using a 30 h protocol, as a significant amount of EO after 24 h was still obtained (Sections S1-S2, Supplementary material). Herein, we report the detailed chemical composition variability of the obtained EO fractions, as well as their preliminary antifungal activity against Candida albicans.

EO extraction
RS is an annual plant (Section S1 of Supplementary material), all the material was collected in the end of July containing flowering and fruiting stages mixed together (Figures S1-S4, Supplementary material). The EO was collected at various fraction times (1, 2, 3, 6, 12, 24 and 30 h). A very unusual yield profile was obtained with two maximum ( Figure S5, Supplementary material). Relative yield percentages of EO samples and total yield over the entire extraction time are shown in Table S1 (Supplementary material). The fraction collection was stopped at 30 h as at higher extraction time no more appreciable amount of EO was accumulated.

GC-MS analysis
The gas chromatographic-mass spectrometry (GC-MS) analysis of 13 RSEO samples revealed the presence of 20 different chemical constituents differently distributed on each fraction (Table S2, Supplementary material). Generally, a substantial difference between the first and the second half of the extraction was observed. Monoterpene o-cymene (OCI) has been found to prevail in the oils extracted up to 6 h, while the phenylpropanoid dill-apiol (DAP) was a characterizing compound in the later fractions. Constituents concentration profiles was found related to the extraction fraction time, but some of them were always present in substantial amounts in all fractions, such as b-pinene (PIN), limonene (LIM), b-terpinene (TER), p-cymen-8-ol (PCY) and piperitenone oxide (PEO). However, their percentages were higher in the Eos obtained with the third (2-3 h) and fourth (3-6 h) fractions. Some other constituents were found present only in specific fractions, sometimes reaching rather high amounts. In particular, a-phellandrene appeared after the third hour to reach a significant amount only in the 3-6 h (16.7%) and in the 6-12 h (5.4%) fractions while p-menth-1(7)-en-2-one started to appear after the second hour, being significant in the sixth (12-24 h, 5.4%) and seventh (24-30 h, 9.7%) fractions. Interestingly, cryptone was revealed between the first and the fifth fraction, with the highest percentage (6.2%) in the second one. Monoterpenoid cis-sabinol appeared as important oil constituent after the second fraction, being particularly abundant in the last one (12.9%). Contrary to this, some others disappeared with the process progress, such as a-pinene and 2,3-pinanediol. Taking all these variations into account, especially the increase of some compounds with the extraction development, the obtained RSEO fractions were quite different between each other. Noticeably, the first fraction's had the lowest complex chemical profile (11 identified compounds), while the others contained more chemical components (from 14 to 19 compounds). To simulate a continuous extractions mixtures were also prepared and analyzed and their profiles reflected quite well the original fractions compositions where OCI and DAP continued to be the main characterizing compounds. However, in the mixtures some deviations could be observed: for example, the yields of cis-sabinol and piperitenone oxide had the opposite evolution than in the original fractions (Table S3, Supplementary material).

Anti-Candida activity
The in vitro antifungal activities of the samples against Candida albicans (ATCC 10231) are reported in Table S4 (Supplementary material). The majority of the RSEO samples showed a weak activity at the used concentration range.

Conclusions
The applied extraction method furnished fractions that differ greatly in their chemical compositions. Monoterpene OCI was found to prevail in the EOs extracted up to 6 h, while DAP characterized the later fractions. The OCI prevalence has not been previously reported for RS, while DAP was not usually the main chemical components (Section S3-S4, Supplementary material). These data, coupled to the low concentration of compounds previously reported for this species (a-phellandrene, cis-b-ocimene and terpinolene), the RSEO from Tarquinia seems could be considered as a new chemotype. Unfortunately many RSEO samples were found not effective against C. albicans. However, therefore further biological investigation are in due course