Date of Award
Doctor of Philosophy (PhD)
Dr. Mohammed Abdul Mohsen Salem Alyafei
Dr. Shyam S. Kurup
Essential Oils (EOs) are expensive hydrocarbons produced exclusively by specific species in the plant’s kingdom. Nowadays, with the growing trends of a healthy lifestyle and enormous research-based discoveries, EOs became a popular, attractive topic, for both research and industry, with revenues reaching billions of dollars annually. The United Arab Emirates (UAE) has rich traditional herbal medicine, associated with topical and EO-aromatherapy applications, that (in most cases) not scientifically justified nor clarified. This dissertation investigated the EO-bearing plants of the UAE, providing a databank with comprehensive knowledge for all indigenous and naturalized EO-bearing plant species of the UAE wildflowers. Also, this work studied EO for one of the common perennial medicinal shrubs of the UAE, which is Aerva javanica (Burm. f.) Juss. ex Schul. (Amaranthaceae). The focus was on EO isolated from leaves and flowers of this shrub, and how different factors (including: postharvest drying methods, particle size, seasonal variation) can significantly influence EO yield quantitatively (by hydrodistillation) and qualitatively (by Gas Chromatography-Mass Spectrometry (GC-MS)). This work aimed to provide a scientific justification for the rich traditional applications of A. javanica, through investigating it is antioxidant activity (in vitro) using DPPH, FRAP, and ABTS assays. Results showed that post-harvest drying methods lead to a significant effect on EO yield qualitatively and quantitatively. Generally, EO of fresh samples provided the best quality yield, while freeze-drying was the best drying method that conserves that quality. Seasonal variations lead to a significant effect on all studied physiological parameters and EO yield qualitatively and quantitatively. Spring was the best season to harvest the best quality EO. Leaves particle size leads to a significant variation on EO yield. A. javanica EO (particularly extracted from leaves) has antioxidant activity (in vitro). Additionally, this dissertation wanted to explore EO of Cleome amblyocarpa Barr. & Murb. (Cleomaceae), which is a medicinal annual herb widespread in the UAE. Studies related to germination and seedling's emergence rate were conducted. The influences of three soil matric potentials were investigated (pF: 1.7 “control”, 1.9 “moderate stress”, 2.1 “high stress”), created by applying three irrigation regimes, and measured by Stevens pF Sensors. Effect of water stress on vegetative growth parameters and yield were recorded (fresh and dry weight basis). Besides, this work studied the influence of the created three pF levels on the EO yield quantitatively (by hydrodistillation) and qualitatively (by GC-MS). Results of GC-MS analysis provided compounds identification for 27, 20, and 17 volatiles, under pF levels of 1.7, 1.9, and 2.1, respectively. Morpho-physiological analyses were conducted by Scanning Electron Microscope (SEM) and spectrophotometer methods. Finally, this dissertation explored (in vitro) the antioxidant activity of C. amblyocarpa EO (extracted from it is seeds and whole plant) using DPPH, FRAP, and ABTS assays. Results showed that C. amblyocarpa is a sensitive desert herb to water availability. Drought stress severity reduced the overall vegetative growth parameters and caused a significant reduction in overall vegetative yield. Drought stress caused significant morpho-physiological variations. The pF at 1.9 is a good stress indicator tool that shows the maximum tolerable water stress level during C. amblyocarpa life cycle. Results showed that this herb is a promising source of phytochemicals that have antioxidant activity (in vitro). This work concluded by adding this species as a new record of the EO-bearing plants, to have in total 136 Emirati EO-bearing plant species, as well as a new natural resource of bioactive antioxidants.
Ramadan Shahin, Suzan Marwan, "THE UNITED ARAB EMIRATES INDIGENOUS ESSENTIAL OIL-BEARING PLANTS: ESSENTIAL OILS OF AERVA JAVANICA AND CLEOME AMBLYOCARPA GROWN IN SANDY SOILS UNDER ARID CONDITIONS" (2018). Dissertations. 114.