Enantiomeric distribution of key volatile components in Citrus essential oils

Abstract

Citrus as many other plants present characteristic distribution of some enantiomers, thus it is often possible to use this parameter for identifi cation, characterization, genuineness, and pharmacological activity assessment. In particular, it is possible to reveal adulteration of different nature, such as addition of synthetic compounds, or natural components of different botanical origin, with drastic changes in the biological and olfactory properties. This study is focused on the evaluation of the enantiomeric excesses of numerous samples of different Citrus species: C. deliciosa Ten., C. limon (L.) Burm., C. bergamia, C. aurantifolia (Christm.) Swing., C. latifolia Tan., C. sinensis (L.) Osbeck, and C. aurantium L. The enantiomeric distribution is determined by direct esGC and, depending on the complexity of the essential oil, by MDGC with a chiral column in the second dimension. The research is focused on the determination of fourteen chiral components which present specifi c distribution in the essential oils investigated. Particular attention is given to the trend of the enantiomeric distribution during the productive season, so to identify useful parameters for quality assessment also in consideration of the wide range of variability often reported in literature. The components investigated were the following: α-thujene, α-pinene, camphene, β-pinene, sabinene, α-phellandrene, β-phellandrene, limonene, linalool, camphor, citronellal, linalyl acetate, terpinen-4-ol, α-terpineol. The use of MDGC allowed the separation of the enantiomers of camphor and citronellal, otherwise not separated by conventional esGC; however for the separation of the enantiomers of α-pinene it was preferable to use conventional esGC. The MDGC system allowed to determine the enantiomeric distribution of camphene, α-and β-phellandrene in lime essential oil for the fi rst time.The results are discussed in function of seasonal variation and, when possible, in function of the extraction technology, with particular regards to lime oils.

Essential Oil Characterization of Thymus vulgaris from Various Geographical Locations

“…d -α-Thujene was the dominant enantiomer in samples #3 and #4, while l -α-thujene predominated in sample #5. The l -enantiomer of α-thujene was found to be predominant in various Citrus essential oils [ 19 ]. l -α-Pinene dominated samples #1 and #3, but d -α-pinene was the major enantiomer in #4.…”

Determination of Volatile Flavour Profiles of Citrus spp. Fruits by SDE‐GC–MS and Enantiomeric Composition of Chiral Compounds by MDGC–MS

“…() and Bonaccorsi et al . (). A double oven MDGC‐MS (Agilent Technologies) was used for analysis of the chiral aroma compounds.…”

“…Citrus fruit species are known to have a large number of characteristic enantiomeric key compounds. Hence, they could be used as the parameter to identify adulteration such as addition of synthetic compounds, or natural components of different botanical origin which may drastically change the biological and olfactory properties of the product (Bonaccorsi et al ., ). In most cases, enantiomeric mixtures occur with one enantiomer predominant and with characteristic biological activities (Werkhoff et al ., ).…”

Relationship between the terpene enantiomeric distribution and the growth cycle of lemon fruit and comparison of two extraction methods

“…Racemization may occur during processing, extraction and storage, as well as due to non-enzymatic reactions such as autoxidation, photo-oxidation and acidity, among others. Several studies demonstrated that the time of harvest affected the composition of essential oils (13,16,33). Fluctuations in the enantiomer ratios in lemon oil according to the season of harvest have been studied (17).…”

“…In case of assessing the authenticity of flavouring on the basis of its enantiomeric composition, knowing the consistency of this composition in nature is essential (14). Some studies have focused on the variation of the essential oil composition and its enantiomeric composition according to the season (15)(16)(17), but to our knowledge, none have evaluated the dependence of the enantiomeric distribution on the growth cycle of a lemon fruit. Citrus fruits have three well-defined growth stages.…”