**3.7 Enzyme-assisted extraction (EAE)**

In some plants, some phytochemicals in their matrices are dispersed in cell cytoplasm, and secondary metabolites are retained in the polysaccharide-lignin network by hydrogen or hydrophobic bonding and are not accessible with a solvent extraction process [45]. Enzymatic pre-treatment has been considered as an effective way to release bounded compounds and increase overall yield [46]. Specific enzymes such as cellulase, a-amylase, and pectinase added during extraction enhance recovery by breaking the cell wall and hydrolyzing the structural polysaccharides and lipid bodies [46, 47]. There are two approaches for enzyme-assisted extraction method namely enzyme-assisted aqueous extraction (EAAE) and enzyme-assisted cold pressing (EACP) [48]. EAAE methods have been employed mainly for the extraction of oils from various seeds [46, 49–51]. In EACP method, enzymes are used to hydrolyze the seed cell wall of a plant [52].

## **3.8 Extraction of volatile organic compounds**

Distillation is the separation process of the components of a mixture of two or more liquids due to their difference in their vapor pressure. The aims of distillation process are to obtain an essential oil. Hydro-distillation (HD), steam distillation (SD), simultaneous distillation solvent extraction (SDE), microwave-assisted hydro-distillation (MWHD), supercritical fluid (CO2) extraction (SFE), purge and trap, and solid phase microextraction (SPME) [53] were employed to extract volatile organic compounds from fresh plant parts. Among these techniques, HD, SD, and SDE are classical and conventional methods for sampling bioactive volatile organic compounds (VOCs). Hydrodistillation is the distillation technique carried out either by boiling the plant materials or essential oil with water by creating the steam. The composition of the oil distillates from a mixture of two liquids depends primarily upon the boiling points or the vapor pressure at the distillation temperature.

Problems connected with conventional methods include long extraction times, large amounts of solvents, and multiple steps. Additionally, many unstable volatile organic compounds may be thermally decomposed and degraded during the thermal extraction or distillation. Because of their simplicity, these methods are still in use to extract fragrance-and-aroma oils from plants. Purge and trap, SFE, and SPME have aroused much attention from analysts as they are environment friendly sampling techniques for bioactive VOCs [53].

## *3.8.1 Purge and trap*

Purge and trap also known as dynamic headspace uses ultra-purified inert gas as the carrier gas to pass through samples continuously to carry out VOCs, and then VOCs are trapped in the trap that contains the sorbent such as Tenax [54]. The type of sorbent in the trap can be varied in order, and purge and trap can achieve high selectivity for different biological VOCs. Properly prolonging sampling time could also improve the enrichment effect [53]. This method has been employed for sampling not only VOCs but also semi-VOCs [55].

### *3.8.2 Solid phase microextraction*

Solid phase microextraction (SPME), developed by Arthur and Pawliszyn [56] and Pawliszyn [57], has been considered as one of the best inventions in extraction of volatile organic compounds in the field of sample [53]. SPME integrates the extraction, concentration, and introduction simultaneously, and the use of this method results in reducing preparation time and simultaneously increasing sensitivity over other extractions [53]. Because of all these advantages, SPME could be considered as a simple, efficient and environment friendly sample extraction method, which has been used in the environmental [58], biological [59], pharmaceutical [60], field analyses [61], and fragrance-and-aroma study [62]. Additionally, headspace solid phase microextraction (HS-SPME) has been considered as an appropriate method for sample preparation in the fragrance and aroma analysis [62].

## **4. Conclusions and future trends**

Plants have provided humans with many of their essential needs, including lifesaving agents for centuries. As only 1–10% of the available higher plant species have been screened biologically, drug discovery from plants should remain an essential component in the search for new medicines [2], particularly with the development of highly sensitive and versatile analytical methods which include search further for convenient extraction methods in future. Botanical insecticides are also getting a lot of attentions in the integrated pest management to produce healthy fruits, vegetables, and crops [63]. Natural ingredients are also gaining popularity, and the use of plant extracts in cosmetic formulation increases [64]. A cosmetic formulation from natural origin can protect the skin against exogenous or endogenous harmful agents and help to remedy many skin-related diseases [64]. Essential oils have been used for thousands of years, as incense, perfumes, cosmetics, and for their medicinal and culinary applications [64]. This book aimed to cover aforementioned areas and others of applications of plant extracts in depth. It is recommended to conduct international multidisciplinary projects for drug discovery from natural sources, and proper utilization of plants in various areas mentioned in this book is important. Thus, there is a need for cooperative effort among scientists to make use of benefits from these resources.

## **Author details**

Aman Dekebo Department of Applied Chemistry, Adama Science and Technology University, Adama, Ethiopia

\*Address all correspondence to: amandekeb@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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