Essential Oils: Historical Significance, Chemical Composition and Medicinal Uses and Benefits

Book Preface

The use of essential oils by civilizations constitutes a common practice since antiquity. In earlier times, China, India and the Middle East used herbs and oils in cooking, cosmetics, medicine and in religious rituals. These substances come from a secondary metabolism of plants and are associated with several functions necessary for their survival, such as the defense against microorganisms, predators and attraction of pollinators. Essential oils are composed of a complex mixture of biologically active substances, lipophilic and volatile, and in most cases derivatives of terpene compounds and in a lower occurrence – phenylpropanoids. They have been long recognized for their medicinal uses: antibacterial, antifungal, antiviral, insecticidal and their antioxidant properties. The increased interest in alternative natural substances is driving the research community to find new uses and applications of these substances. This book provides research on the historical significance, chemical composition and medicinal uses and benefits of essential oils. Some of the topics discussed include extraction methods of essential oils; an overview of the most relevant essential oil changes regarding plant phenology and plant development; the antibacterial properties of some essential oils; essential oils applications in agriculture; and the use of essential oils as additives in broiler diets.

Chapter 1 – The use of essential oils has been a common practice in human societies since antiquity. The ancient civilizations of China, India, and the Middle East were already using herbs and oils in cooking, cosmetics, medicine, and religious rituals. These substances derive from plant secondary metabolism and are associated with several functions necessary for their survival, such as defense against microorganisms and predators and attraction of pollinators. Essential oils are composed of a complex mixture of biologically active substances, lipophilic and volatile, in most cases derivatives of terpene compounds and, to a lesser extent, phenylpropanoids. In recent years, interest in these substances has intensified due to the numerous properties associated with them, such as analgesic, expectorant, antimicrobial, antiseptic, insecticidal, fungicidal, and bactericidal qualities. These latter properties in particular have aroused the interest of many researchers in different parts of the world, seeking alternative products to replace synthetic insecticides and fungicides, due to the risks posed by the latter to health and ecosystems. The properties of essential oils make them good candidates for use in the production of medicines and natural insecticides.

Chapter 2 – The biosynthesis of the essential oils can be affected by a number of factors, mainly genetic and environmental ones. These potential variations in their chemical composition can occur and have been the subject of many researchers. Since many of the most commercially important species are perennial species, their harvest time and cultivation conditions can be upgraded through better knowledge of the variations in the phenology in order to improve yields and quality of their essential oil. Furthermore, examining thetrend of qualities and yields over 5, 6 or even more years throughout the plant development provides a key tool for the strategic establishment of new promising species as alternative crops. Producers are interested in these alternative crops that may improve the environmental and
composition of the essential oils is mainly determined by individual variations and, therefore, is largely subjected to a genetic control. However, ontogeny changes throughout phenology can cause more or less pronounced variations in a few compounds of the whole essential oil chemical spectra. Notwithstanding these slight variations in chemical composition, the phenological stages have a greater influence on the yields obtained from distillation of dry material. The most recent published data leads to the suggestion that although flowering time is the most common harvest time for essential oil, producing plants may not always be in line with the highest yields. Herein, the authors provide an overview of the most relevant essential oil changes regarding plant phenology and plant development, summarize the latest reports related to the monitoring of essential oil production, and outline their implications for productivity and quality.

Chapter 3 – Essential oils (EOs) are natural volatile complex blends of biologically active molecules used nowadays for a panoply of applications. Presently, their importance have been highlighted due to the increasing demand by the food and pharmaceutical industries but also for their potential to provide therapeutic benefits in the prevention and management of diseases. In view of the multiple applications of the EOs, it is becoming important to explore different extraction techniques for higher yields of EOs as well as for the isolation of new biologically active compounds. This chapter attempts to highlight recent extraction techniques for obtaining EOs from medicinal aromatic plants. The conventional extraction techniques, their optimisation and improvements are discussed through the innovative principles, their benefits and disadvantages. Moreover, this chapter also endeavors to provide an up-to-date literature on EOs, the reported traditional usage of EOs from medicinal and aromatic plants of Mauritius, common extraction methods, bioactivities, and applications.