Review on essential oil extraction from aromatic and medicinal plants: Techniques, performance and economic analysis

Highlights

• Essential oil extraction from aromatic and medicinal plants.

• Analysis of various essential oil extraction methods.

• Performance analysis of different oil extraction techniques.

• Economic and environmental aspects of conventional and non-conventional oil extraction methods.

Abstract

Essential oils extracted from herbal plants have many foods, cosmetic and medical industries applications. Present study discussed various conventional extraction techniques (steam distillation, hydro-distillation, hydro diffusion and solvent extraction) and advanced (non-conventional) extraction techniques (solvent free microwave extraction, subcritical extraction liquid and supercritical fluid extraction). Economic analysis, kinetics modelling, and GC-MS analysis of essential oil produced by various extraction techniques have also been presented. India is the biggest producer of Indian basil oil and Japanese peppermint oil, and USA is the major importer and exporter of EOs with 14% (US$390.9 m) of world imports and 17% (US$351.7 m) of world exports. Production cost for Steam distillation, Water distillation, solvent extraction and Supercritical fluid extraction varies from 15.85 - 76.50US$/kg, 7.05-86.4US$/kg, 8.35-8.53US$/kg and 6.71-42.69US$/kg, respectively. Second order model are consistent with experimental data as determination coefficient (R²) is higher than first order model. Non-conventional extraction methods are superior to conventional extraction methods in terms of low cost, time and energy saving, less solvent requirements, shorter extraction time, etc. From the techno-economic and environmental perspective, water distillation with full energy integration is the best method for rosemary oil. In contrast, supercritical fluid extraction is the best method for oregano oil.

Introduction

European Pharmacopeia 7th edition (Asbahani et al., 2015) defines essential oils as “aromatic products with a mixture of compounds derived from plant raw material, either separated by steam, dry distillation, or by a suitable mechanical technique without heating.” Essential oil is separated from liquid phase without changing its chemical composition by physical method. Herbal plants are very important as most of the population depends on products of these plants (essential oils). The products of these plants are used in food, cosmetic items and medical field etc. (Kant and Kumar, 2021). Various extraction techniques are used for essential oil (EO) extraction from several parts of medicinal plants, such as barks, peels, leaves, buds, seeds, flowers etc. (Tongnuanchan and Benjakul, 2014). The methods used to extract essential oil from these plants are; steam distillation (SD), solvent-assisted extraction, hydro distillation (HD), ultrasonic-assisted extraction, supercritical fluid extraction and solvent-free microwave extraction (Belhachat et al., 2018). Oil extraction techniques are classified as shown in Fig. 1. Conventional methods of essential oil extraction have lower yield and efficiency and higher extraction time than non-conventional methods such as microwave-assisted extraction and ultrasonic-assisted extraction. However, they are still used for essential oil extraction nowadays. Non-conventional methods produce higher yield, require low cost and have relatively short extraction time (Kusuma and Mahfud, 2017, 2018).

Essential oils extracted from medicinal plants are also used for health benefits, as illustrated in Fig. 2.

Various studies have been carried out on the methods of oil extraction from aromatic and medicinal plants. Afzal et al. developed a hybrid solar distillery to extract oil from peppermint leaves and eucalyptus. A secondary biomass system was also attached to meet energy demand during rainy season and night hours (Afzal et al., 2017). Munir et al. extracted EOs from aromatic plants by solar steam distillation system (SSDS) (Munir et al., 2014). Phineas Masango used SD to extract essential oil from vegetable raw material. Results show that steam flow rate affects oil yield (Masango, 2005). Nazem et al. applied hydro distillation to extract EOs from Mentha (peppermint) species and evaluated essential oil yield, phenolic content and essential oil composition (Nazem et al., 2019). Razzaghi et al. designed and developed a condenser to extract herbaceous oil. Condenser performance was evaluated in this study by utilizing two refrigerants named R12 and R134a. Refrigerants were used to separate oil and water from mentha leaves by vapour and air mixture (Razzaghi et al., 2019). Sowbhagya et al. extracted oil from cumin seed by hydro distillation process. Flaking process was used for size reduction of cumin seed in place of conventional method. This study evaluated the effect of flaking on quality of oil and yield (Sowbhagya et al., 2008). Kusuma et al. used solvent free microwave extraction (SFME) for basil oil extraction and compared it with microwave hydro-distillation (MHD). Results showed that SFME has higher yield and shorter extraction time than MHD (Kusuma and Mahfud, 2017).

Essential oils are very important as they are used as anti-cancer agents, anti-viral agents, anti-spasmodic effects, anti-bacterial agents, anti-diabetic activity, and anti-lipid peroxidation etc. Present study aims to summarize all oil extraction methods and their economic and environmental aspects. Not a single review article has been published on extracting oils from medicinal plants, system performance and their economic and environmental aspects in the Indian region. This will be helpful for researchers to find out best essential oil extraction method for a particular medicinal and aromatic plant. From the techno-economic and environmental perspective, water distillation with full energy integration is the best method for rosemary oil. For oregano oil, supercritical fluid extraction is the best method.