**1. Introduction**

Aromatic plants have been used since ancient times for their preservative and medicinal properties, and to impart aroma and flavor to food. Hippocrates, sometimes referred to as the "father of medicine," prescribed perfume fumigations. The pharmaceutical properties of aromatic plants are partially attributed to essential oils. The term "essential oil" was used for the first time in the sixteenth century by Paracelsus von Hohenheim, who named the effective component of a drug, "Quinta essential" [1]. By the middle of the twentieth century, the role of essential oils had been reduced almost entirely to use in perfumes, cosmetics and food flavorings, while their use in pharmaceutical preparations had declined.

The natural mixtures of volatile and aromatic compounds (Essential oils) are secondary aromatic plant metabolites. Essential oils are complex, multi-component systems composed mainly of terpenes in addition to some other non-terpene components. Several techniques can be used to extract essential oils from different parts of the aromatic plant, including hydrodistillation (HD), solvent extraction and supercritical fluid extraction (SFE) [2]. Essential oils are derived from various parts of the plant, including leaves, flowers, fruits, seeds, rhizomes, roots, and bark. In the plant, these constituents serve several physiological purposes for the plant protection from pests and microorganisms, attraction of pollinating insects or birds, providing photoprotection to the plant, and allelopathy.

Essential oils are usually obtained by steam or hydro-distillation first developed in the Middle Ages by Arabs. Known for their antiseptic, i.e., bactericidal, virucidal and fungicidal, and medicinal properties and their fragrance, they are used in embalmment, preservation of foods and as antimicrobial, analgesic, sedative, anti-inflammatory, spasmolytic and locally anesthesic remedies. Up to the present day, these characteristics have not changed much except that more is now known about some of their mechanisms of action, particularly at the antimicrobial level. In nature, essential oils play an important role in the protection of the plants as antibacterials, antivirals, antifungals, insecticides, and also against herbivores by reducing their appetite for such plants. They also may attract some insects to favor the dispersion of pollens and seeds, or repel undesirable others. Essential oils are extracted from various aromatic plants generally localized in temperate to warm countries like Mediterranean and tropical countries where they represent an important part of the traditional pharmacopeia. They are liquid, volatile, limpid and rarely colored, lipid soluble and soluble in organic solvents. Essential oils can be synthesized by all plant organs, i.e., buds, flowers, leaves, stems, twigs, seeds, fruits, roots, wood or bark, and are stored in storage cells like cavities, canals, epidermic cells or glandular trichomes [3, 4]. Most of the commercialized essential oils are chemotyped by gas chromatography and mass spectrometry analysis. Analytical monographs have been published (European Pharmacopoeia, ISO, WHO, Council of Europe; [5]) to ensure good quality of essential oils.

Essential oils have been largely employed for their properties already observed in nature, i.e., for their antibacterial, antifungal and insecticidal activities. At present, approximately 3000 essential oils are known, 300 of which are commercially important especially for the pharmaceutical, agronomic, food, sanitary, cosmetic and perfume industries. Essential oils or some of their components are used in perfumes and make-up products, in sanitary products, in dentistry, in agriculture, as food preservers and additives, and as natural remedies. For example, d-limonene, geranyl acetate or d-carvone are employed in perfumes, creams, soaps, as fragrant components and in food, as natural flavoring agents fragrances for household cleaning products and as industrial solvents. Moreover, essential oils are used in massages as mixtures with vegetal oil or in baths but most frequently in aromatherapy. Some essential oils appear to exhibit particular medicinal properties that have been claimed to cure one or another organ dysfunction or systemic disorder [6–8].

Essential oils have traditionally been used to impart flavoring or preservative effects to foods, or to instill fragrances in cosmetics and aromatherapy. Since ancient times, numerous civilizations have also valued essential oils for their therapeutic qualities in disease prevention and treatment. Later, the Greeks and Romans absorbed Egyptian practices of using essential oils in aromatherapy and expanded it to their baths for promotion of well-being. For instance, baths infused

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*Essential Oil as Antimicrobial Agents: Efficacy, Stability, and Safety Issues for Food Application*

with the oils of jasmine, lavender, or ylang-ylang stimulated mental relaxation. Similarly, current interest in essential oils arises from the various bioactive effects they display, including antioxidant [9, 10], anti-inflammatory [11, 12], antimicrobial [13, 14], antiviral [15, 16], and anticarcinogenic [17]. In developed countries, the benefits derived from using essential oils appear optimistic. Demand for plant essential oils has risen as a consequence of consumers searching for cheaper, more 'natural' alternatives to disease-fighting medications. In food and cosmetic applications, essential oils are considered to be biodegradable, readily available, and 'less toxic' than synthetic preservative agents. As such, this optimism has raised concerns and stimulated studies to evaluate the safety and efficacy of essential oils in various systems in order to better understand their pharmacological properties and

Today there is significant consumer demand for foods that are minimally processed and free from synthetic chemical preservatives with the perception of being "natural" [18, 19]. As a result the food industry is facing great challenges to produce naturally occurring food antimicrobials and antioxidants to reduce the use of synthetic chemical preservatives and still produce safe foods that are also regarded as healthy. Spices and herbs are well known for their antimicrobial and antioxidant properties and have the ability to produce multidimensional flavors in food [20]. The clove, cinnamon, oregano and rosemary are considered as the most common spices and herbs with strong antimicrobial activity. Their essential oils containing chemical compounds such as carvacrol, cinnamaldhyde, eugenol and camphor are identified as the major chemical components responsible for exerting antimicrobial activity [21–24]. Some studies reported that there is a highly positive linear relationship between antioxidant activity, antibacterial activity and total phenolic content

Antimicrobials are used in food for two main reasons: (1) to control natural spoilage processes (food preservation) and (2) to prevent/control growth of micro-organisms, including pathogenic micro-organisms (food safety). Natural antimicrobials are derived from animal, plant and microbial sources. There is considerable potential for utilization of natural antimicrobials in food, especially in fresh fruits and vegetables. However, methods and mechanisms of action, as well as the toxicological and sensory effects of natural antimicrobials, are not

There are more than 1340 plants with defined antimicrobial compounds, and over 30,000 components have been isolated from phenol group-containing plant-oil compounds and used in the food industry. However, commercially useful characterizations of preservative properties are available for only a few EOs. There is a need for more evaluation of EOs in field and food systems. Food-preservative utilization of spices and their EOs as natural agents has recently been focused on extending the shelf life of foods, reducing or eliminating pathogenic bacteria, and

Essential oils are very complex natural mixtures which can contain about 20–60 components at quite different concentrations. They are characterized by two or three major components at fairly high concentrations (20–70%) compared to others components present in trace amounts. For example, carvacrol (30%) and thymol (27%) are the major components of the *Origanum compactum* essential oil, linalool (68%) of the *Coriandrum sativum* essential oil, a- and b-thujone (57%)

*DOI: http://dx.doi.org/10.5772/intechopen.92305*

roles in health.

in some spices and herbs [25, 26].

completely understood [18, 27–30].

**2. Composition of essential oils**

increasing overall quality of food products [27, 31–35].

#### *Essential Oil as Antimicrobial Agents: Efficacy, Stability, and Safety Issues for Food Application DOI: http://dx.doi.org/10.5772/intechopen.92305*

with the oils of jasmine, lavender, or ylang-ylang stimulated mental relaxation. Similarly, current interest in essential oils arises from the various bioactive effects they display, including antioxidant [9, 10], anti-inflammatory [11, 12], antimicrobial [13, 14], antiviral [15, 16], and anticarcinogenic [17]. In developed countries, the benefits derived from using essential oils appear optimistic. Demand for plant essential oils has risen as a consequence of consumers searching for cheaper, more 'natural' alternatives to disease-fighting medications. In food and cosmetic applications, essential oils are considered to be biodegradable, readily available, and 'less toxic' than synthetic preservative agents. As such, this optimism has raised concerns and stimulated studies to evaluate the safety and efficacy of essential oils in various systems in order to better understand their pharmacological properties and roles in health.

Today there is significant consumer demand for foods that are minimally processed and free from synthetic chemical preservatives with the perception of being "natural" [18, 19]. As a result the food industry is facing great challenges to produce naturally occurring food antimicrobials and antioxidants to reduce the use of synthetic chemical preservatives and still produce safe foods that are also regarded as healthy. Spices and herbs are well known for their antimicrobial and antioxidant properties and have the ability to produce multidimensional flavors in food [20]. The clove, cinnamon, oregano and rosemary are considered as the most common spices and herbs with strong antimicrobial activity. Their essential oils containing chemical compounds such as carvacrol, cinnamaldhyde, eugenol and camphor are identified as the major chemical components responsible for exerting antimicrobial activity [21–24]. Some studies reported that there is a highly positive linear relationship between antioxidant activity, antibacterial activity and total phenolic content in some spices and herbs [25, 26].

Antimicrobials are used in food for two main reasons: (1) to control natural spoilage processes (food preservation) and (2) to prevent/control growth of micro-organisms, including pathogenic micro-organisms (food safety). Natural antimicrobials are derived from animal, plant and microbial sources. There is considerable potential for utilization of natural antimicrobials in food, especially in fresh fruits and vegetables. However, methods and mechanisms of action, as well as the toxicological and sensory effects of natural antimicrobials, are not completely understood [18, 27–30].

There are more than 1340 plants with defined antimicrobial compounds, and over 30,000 components have been isolated from phenol group-containing plant-oil compounds and used in the food industry. However, commercially useful characterizations of preservative properties are available for only a few EOs. There is a need for more evaluation of EOs in field and food systems. Food-preservative utilization of spices and their EOs as natural agents has recently been focused on extending the shelf life of foods, reducing or eliminating pathogenic bacteria, and increasing overall quality of food products [27, 31–35].
