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Essential oils are highly volatile, aromatic concentrated extracts from plants with wide applications. In this study, fast, easy-to-use attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was combined with chemometric techniques to verify essential oils’ taxonomy and purity. Principal component analysis (PCA) clustered 30 essential oil samples into three different groups based on plant botanical family and concentration. The first group contained highly concentrated oils from the Asteraceae family, the second group contained highly concentrated oils from the Lamiaceae family, while the last group contained three highly concentrated essential oils from different botanical families and commercial-grade essential oils. Thus, commercial-grade oil samples did not cluster with the corresponding concentrated oil samples despite their similar spectral patterns or botanical family. A loading plot identified infrared (IR) bands that correspond to carbonyl, vinyl, methyl and methylene group vibrations as the most important spectral bands that can be used as marker bands for discrimination between different botanical plant family groups. Hierarchical cluster analysis (HCA) confirmed the results obtained by PCA. ATR-FTIR spectroscopy combined with chemometric algorithms provides a direct and non-destructive method for chemotaxonomic classification of medicinal and aromatic essential oils and an assessment of their purity.

As total life expectancy increases, the prevalence of age-related diseases such as diabetes and Alzheimer’s disease is also increasing. Many hypotheses about Alzheimer’s disease have been developed, including cholinergic neuron damage, oxidative stress, and inflammation. Acetylcholine is a major neurotransmitter in the brain and cholinergic deficits leads to cognitive dysfunction and decline. Recent studies have linked diabetes as a risk factor in developing Alzheimer’s disease and other types of dementia. The incidence of patients with type II diabetes and increased levels and activity of α-amylase is higher in patients with dementia. It has been shown that aromatherapy with essential oils from the mint family can improve cognitive performance in Alzheimer’s disease patients. Selected monoterpenoids from these essential oils are reported to inhibit acetylcholinesterase, both in vitro and in vivo . Terpenoids are small, fat-soluble organic molecules that can transfer across nasal mucosa if inhaled, or penetrate through the skin after topical application, enter into the blood and cross the blood-brain barrier. Recent evidence supports the idea that the common constituents of essential oils also inhibit α-amylase, a starch digestive enzyme that plays an important role in the control of diabetes. The mint family is a fragrant plant family that contains most of the culinary herbs found in the Mediterranean diet. The Mediterranean diet is considered to be one of the healthiest diets in the world, and is found to be beneficial not only for the heart but also for the brain. Herbs used in this diet are rich in antioxidants that can prevent oxidative damage caused by free radicals. However, our study shows that they also contain biologically active compounds with potent α-amylase and acetylcholinesterase inhibitory activities. Consumption of fresh herbs can help boost memory and reduce sugar levels in the body. The use of herbs as a functional food could lead to significant improvements in health. Cognitive stimulation with medical food and medical herbs could delay development of cognitive decline, and improve the quality of life of Alzheimer’s disease patients. This effect can be enhanced if combined with aromatherapy, topically or by inhalation, and/or by ingestion. Terpenes and terpenoids, the primary constituents of these essential oils are small, lipid soluble organic molecules that can be absorbed through the skin or across nasal mucosa into the systemic blood circulation. Many terpenes can also cross the blood-brain barrier. Therefore, topical application or inhalation of essential oils will also produce a systemic effect.

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This review is part 10 of a series of contributions by the critical properties group of the previous IUPAC Commission I.2 on Thermodynamics, Subcommittee on Thermodynamic Data and the present IUPAC Project #2000-026-1-100, Critical Compilation of Vapour Liquid Critical Properties, sponsored by the Physical and Biophysical Chemistry Division. It presents all known experimental data for the critical constants of hydrocarbons containing halogens. Recommendations are given together with uncertainties. Critical temperatures have been converted to ITS-90, and the molar masses are based on the relative atomic masses recommended by the IUPAC-CIAAW in 2005.

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