Exploiting the bioactive properties of essential oils and their potential applications in food industry

Abstract

Fruits are an abundant source of minerals and nutrients. High nutritional value and easy-to-consume property have increased its demand. In a way to fulfil this need, farmers have increased production, thus making it available for consumers in various regions. This distribution of fruits to various regions deals with many associated problems like deterioration and spoilage. In a way, the common practices that are being used are stored at low temperatures, preservation with chemicals, and many more. Recently, edible coating has emerged as a promising preservation technique to combat the above-mentioned problems. Edible coating stands for coating fruits with bioactive compounds which maintains the nutritional characteristics of fruit and also enhances the shelf life. The property of edible coating to control moisture loss, solute movement, gas exchange, and oxidation makes it most suitable to use. Preservation is uplifted by maintaining the nutritional and physicochemical properties of fruits with the effectiveness of essential oils. The essential oil contains antioxidant, antimicrobial, flavor, and probiotic properties. The utilization of essential oil in the edible coating has increased the property of coating. This review includes the process of extraction, potential benefits and applications of essential oils in food industry.

Introduction

The presence of various types of microbes is the primary reason why food gets spoiled (bacteria, yeasts, and molds). Manufacturers, distributors, and customers are all impacted financially by this issue. More than 20% of all food produced worldwide is thought to be damaged by bacteria (Sauceda et al, 2011). Food preservation requires the regulation of physical, chemical, and especially microbial variables (Karabagias et al, 2011; Sauceda, 2011). Consumers now favour foods that are simple to prepare, of high quality, are secure, organic and minimally refined, but have a longer durability. With the use of food conservation technology, items can be produced that are longer-lasting while retaining their original nutritional and sensory qualities (Sivakumar et al, 2014; Zhou et al, 2010). Synthetic preservatives, most often antimicrobial defence, have been used in the edible product business for a long time, however current research suggests that consuming chemical additives can cause intoxications, allergies, cancer, and other disorders (Aminzare et al, 2016). Because of this, buyers depreciate them, which drives the need to hunt for alternatives. New natural antibacterial agents have been discovered through this research as replacements for those previously employed ( Gyawali & Ibrahim, 2014; Hayek et al, 2013).

Natural conservation, which refers to using naturally occurring antimicrobial preservatives found in plants, animals, or microorganisms, is one of the alternatives that has received more attention. This is particularly true of extracts made from the various kinds of plants and plant parts used as flavouring in some foods (Macwan et al, 2016). Antimicrobials are used in food to prevent microbial development and regulate natural processes that cause food to decay (Tajkarimi et al, 2010). Extracting, purifying, stabilising, and incorporating these antimicrobials into food products without compromising their sensory quality and safety is challenging (Sauceda, 2011).

As per the research of Sanchez-González et al. (2011), Essential oils (EOs) are colourless liquids that are predominantly made up of the aromatic and volatile molecules that are found in all parts of plants, along with the flowers, seeds, peel, bark, stems, and whole plants. They are mostly utilised as food preservatives, medicines, fragrances, and cosmetics in many different nations. Due to their scent and flavour, they were initially utilised as medicine. Because of its strong scent, around 300 different varieties of EOs have been identified and are being employed in perfumery (Burt, 2004). De la Croix was the first to note that the secondary metabolites, particularly the EO vapours, had antibacterial properties (Boyle, 1955). Since then, several biological activities, including insecticidal (Kim et al, 2003), antifungal (Fitzgerald et al, 2003) antibacterial (Oussalah et al, 2007) and antiviral (Schnitzler et al, 2007) activities, have been reported to be shown by EOs and their phytoconstituents. Most vegetable seeds, including perilla and sunflower seeds, include heterocyclic chemicals like pyrazine, which are essential to the flavour and quality of the products. Vegetable seed oils are also rich in proteins and vitamins (Li & Hou, 2018). Generally speaking, the principal sources of diverse volatile chemicals, which are in charge of numerous biological activities, are Siddha and Ayurvedic medicinal plants. For instance, the main volatile substances, such as alcohol, alkenes, and esters, are considered to be significant components of EOs and to have significant pharmacological effects (Satyavani et al, 2015).

Since they are used as flavours (Scragg, 2007), as fragrances in shampoos or lotions and for skin and hair rejuvenation (Sadgrove, 2018; Sadgrove and Simmonds, 2021), as fragrance, in taper, fluid, detergent that disinfect, and in traditional aromatherapy, essential oils and natural volatiles are the most successful commodities of industry (Sadgrove et al, 2021). Because of the high demand, considerable profits can be made by selling essential oils or their constituent parts at the lowest possible cost. This gives people the incentive to look at supply-side shortcuts (Sadgrove et al, 2021), use fakes or adulterants, or create them through synthesis or in a bioreactor. Consumers prefer, on the whole, that their essential oils come from plants, as in the traditional method. If synthetic essential oils are created using genetically engineered yeasts in a bioreactor (Carsanba et al, 2021) or plant cell cultures (Ochoa-Villarreal et al, 2016) rather than through conventional synthesis, which employs potentially hazardous chemicals, some consumers may be willing to tolerate them. Industrial applications and biological properties are represented in Fig. 1.

Fig. 1.

Bioactive properties of essential oil

This concern is justified since fixed oils like sunflower, mustard, or canola oil are frequently advertised as “pure” essential oils after being scented with a few drops of fragrance. Additionally, some fixed oils made from aromatic plants are labelled as “essential oils,” which suggests a higher-quality product (Sadgrove et al, 2021). Typically, an essential oil is a combination of volatile organic substances made using a particular distillation process, such as Steam distillation, dry distillation assisted by microwaves, or hydrodistillation (Sadgrove, 2018). Since it is false to state that essential oils are naturally present in aromatic plants; instead, essential oils are a result of distillation (Sadgrove et al, 2021).

Elements of essential oils

EOs is made up of combinations of more than 50 different scent components, making them incredibly complex. Examples of EOs include tea tree oil, clove oil, lemon oil, cinnamon oil, mustard oil, oregano oil, lavender oil, eucalyptus oil, peppermint oil, and others. Cinnamomum zeylanicum has bark, leaves, and roots that can be used to make cinnamon oil, a volatile substance. Eugenol, trans-cinnamaldehyde, and linalool (obtained from the bark extract) are three significant ingredients that make up 82.5% of the entire makeup. The primary active component of cinnamon essential oils is cinnamon aldehyde, which has been shown to have growth-inhibitory impacts on a numerous pathogen, consisting both gram-negative bacteria and gram-positive and (Ramage et al, 2012; Pereira et al, 2014). According to several researches, cinnamon essential oils also demonstrated anti-inflammatory, anti-parasitic, and free radical-scavenging capabilities (Terzi et al, 2007). Furthermore, terpinene, terpinen-4-ol, 1,8-cineole, terpinene, terpineol, p-cymene, and terpinene were the primary constituents of tea tree oil (TTO) derived from Melaleuca alternifolia (Myrtaceae) attributed to its components such as 1,8-cineole, -myrcene, -terpineol, terpinen-4-ol, -pinene, -pinene, and linalool, tea tree exhibits excellent antibacterial, germicidal, and anti-microbial activity (e.g, a reduction of 73.8% in Candida species.). When applied at rates of 100 and 200 l/ml, it has been reported that its bioactive components exhibit excellent antioxidant activity, whereas its essential oils exhibit significant free radical scavenging activity ranging from 60 to 80%. Tick control has been tested using tea tree’s insecticidal and acaricidal capabilities (Chaieb et al, 2007). On fungus strains, it had a high inhibitory action (Benabdelkader et al, 2011). The phenylpropanoids, including eugenol, carvacrol, thymol, eugenyl acetate, -caryophyllene, cinnamaldehyde, and 2-heptanone, are the main constituents of clove oil, which is primarily derived from clove buds. Among these, eugenol is frequently employed as an antibacterial agent, has the potential to lessen the production of ergosterol, a particular component of cell walls, and has the potential to prevent C. albicans’ germ tubes from forming. It demonstrated substantial levels of inhibitory effects and radical scavenging activity on multi-resistant Staphylococcus spp. when evaluated versus tert-butylated hydroxytoluene (Végh et al, 2012). Linalool, 1, 8-cineole, lavandulyl acetate, viridiflorol, B-ocimene, terpinen-4-ol, l-fenchone, and camphor have all been shown to be key constituents of lavender oil, which is primarily derived by steam distillation from the family Lamiaceae, particularly Lavandula angustifolia. (Prashar and Locke, 2004; Said et al, 2015). The levels of these chemicals’ concentration, however, varied from one species to other. One of the active ingredients in lavender oil is linalool (Said et al, 2015). Antibacterial action against yeast, dermatophytes, Aspergillus strains, Cryptococcus neoformans, and C. species was demonstrated using lavender oil (Posadzki et al, 2012; Sartorelli et al, 2007). 1, 8-cineole is the main ingredient in eucalyptus oil, but it also contains additional substances including transpinocarveol, p-cymene, cryptone, -terpineol, globulol, phellandral, limonene, cuminal, aromadendrene spathulenol, and terpinene-4-ol (Tyagi and Malik, 2011). Eucalyptus EOs are mostly utilised as flavouring agents and have demonstrated strong activity in inhibiting the growth of food-stuffing and pathogenic bacteria (Lambert et al, 2001; Saharkhiz et al, 2012).

The bioactive components of EOs, in particular the compounds that are antibacterial and antifungal, may focus various chemical pathways or cell structures, such as the deterioration of cell walls, harm to membranes, deformation of proton motive force, etc. Data on the antifungal and antibacterial properties of eucalyptus oil, however, is scarce. Instead of a single molecule, it was found that the antibacterial activity was strongly correlated with the synergistic interactions among the minor and major and chemicals found in eucalyptus oil (Tyagi & Malik, 2011). EOs from Eucalyptus odorata, one of the eight eucalyptus species, shown potent cytotoxic effects and inhibitory actions versus S. aureus, S. pneumoniae, H. influenza, and S. pyogenes (Tyagi & Malik, 2011). On Staphylococci, peppermint oil had extremely strong growth inhibitory properties. Numerous studies found that it effectively combated both azole-resistant and azole-susceptible strains of the Candida species (Cox et al, 2008).

Classification of essential oils

Chemically, various categories of essential oil ingredients are distinguished: The size or quantity of carbon atoms in the fundamental source of biosynthesis, The “skeleton” or backbone of the parent, The type of oxidation caused by electronegative atoms, such as nitrogen, oxygen, or sulphur, which are larger than carbon atoms. Three biosynthetic classes of essential oil constituents, phenylpropanoids, terpenes, or isothiocyanates, are produced by four primary biosynthetic processes. They come from methylerythritol and mevalonate (Zhao et al, 2013), shikimate (Santos-Sánchez et al, 2019), and glucosinolate (Malka and Cheng, 2017), and biosynthetic pathways, respectively. However, the Essential oils can further be categorised in a different way depending on the extraction processes, chemical composition etc.

Classification based on chemical composition

Many distinct types of chemicals are found in the essential oils which are found in the various plants. Pine and citrus both include a substance made only of carbon and hydrogen atoms known as hydrocarbon. The terpene compound found in peppermint, coriander, and tea plants is connected to alcohol by the hydroxyl group (OH). In Citronella, lemon balm, and lemon myrtle, you can find terpenoids having a carbonyl group (C = O) attached to a carbon with hydrogen. Cinnamon, bitter almonds, and cumin are common sources of cyclic aldehydes, which are composed of an aldehyde group connected to a benzene ring (Thrun et al, 2018). A carbonyl group is linked to with two atoms of carbon in ketone. Plants like pennyroyal, sage, thuja, and eucalyptus radiate these, among others (Rolf, 2004). Thyme and oregano are examples of phenol, which has a hydroxyl group connected to a benzene ring (Park, 2011). Between the C and benzene rings in phenolic ether is an O ring. Oxide is a compound found in wormseed, eucalyptus, and cajeput that has an O bridging two or more carbons (Lawless, 2013). Esters, such as those found in lavender, wintergreen, and clary sage, are the condensation-product of acid and alcohol (Aggarwal et al, 2013). German chamomile as well as yarrow have sesquiterpenes that are anti-inflammatory and antiviral; Elecampane and arnica contain sesquiterpene lactones that are mucolytic and immune-stimulating; and aniseed, tarragon, clove, and myrtle leaf contain phenylpropanes that are carminative and anaesthetic (Jones, 2011; Ludwiczuk et al, 2017).

Classification based on extraction methods

Depending on how they were extracted, essential oils can be categorised. Although there are other extraction techniques utilised today, steam distillation, cold pressing, and solvent extraction are the most common. These techniques permit the division of essential oils into four categories: Absolutes or concretes, Steam-distilled, Expressed, Solvent-extracted.

Steam-distilled oils

The earliest and most conventional method of extracting oil is steam distillation (Ozel & Kaymaz, 2004). With this technique, impurity-free, pure oil is produced by the extraction of pure aromatherapy oils. To conclude the procedure, plant material is kept in a container and steam is pumped through it. The temperature of the steam encourages the clusters of aromatic compounds and oils in the plant to release. These molecules are liberated, rise with the steam, and move through a sealed system. Then the fragrant steam is cooled and distilled with cold water after going through a cooling procedure. The essential oils condense and change into a liquid state throughout this process (Dima and Dima, 2015; Wenqiang et al, 2007). Later, the liquid mixture is divided into two components: aromatic water or hydrosol and essential oils (Rao, 2012). During steam distillation, various elements, including the steam pressure passing via plant material, the coolant used, the closed system temperature while oil production, are taken into account (Casselm et al, 2009). All of these elements, along with the distiller’s ability, determine the purity and quality of an oil. Known distillers’ oils are highly regarded because of the calibre and purity of their extracts (Battaglia, 2003).

Cold-pressed or expressed oils

The citrus fruit family produces oils from the peel of several fruits, including grapefruits, oranges, lemons, tangerines, and others, and these oils are extracted using this technique. Despite just being referred to as manifest oils, they are categorised as essential oils because of their significant therapeutic significance. With the aid of mechanical pressure, oils are extracted from the fruits as juice (Roux-Sitruk, 2008). Oils are separated from water using a separation method since the luscious form of oils contains a plenty of water. Cold-pressed oils spoil more faster than other essential oils, that is a drawback of this technique. Therefore, it is advised that these oils be purchased in tiny amounts and replenished as needed (Ryman, 2012).

Solvent extracted oils

Some plant materials cannot withstand cold pressing or heat (in the form of steam). When they go through one of these processes, the oil that is created could be tainted or of poor quality (Handa, 2008). To avoid this, few plants, such as Rose, Jasmine, Tuberose, Orange Blossom (Neroli) are extracted using solvents. Ethanol, methanol, ether, hexane, petroleum and alcohol like solvents are used to obtain useful oils (Singh et al, 2014). Plant materials are processed using hydrocarbon solvents in this way. Essential oils are created by filtering and distilling the solvent mixture under low pressure (Aizpurua-Olaizola et al, 2015). One drawback of this approach is that, occasionally, solvent remnants stay in the oils, which can give certain people allergic responses.

Aroma-based categorization

Additionally, essential oils can be categorised according to their aroma or scent. Citrus, Medicinal/Camphorous, Herbaceous, Floral, Woody, and Resinous, Minty, Earthy, and Spicy oils are among the subcategories in this group of oils (Weyerstah et al, 1993).

Citrus oils

This category consists of essential oils with pronounced citrus flavours. Numerous plants, including those that produce bergamot, grapefruit, lime, lemon, orange, and tangerine, produce citrus oils (Viuda-Martos et al, 2008).

Herbaceous oils

Otherwise, the most beneficial herbs are those that can be made into oils. Some of these plants, including Basil, Clary Sage, Chamomile, Melissa, Hyssop, Peppermint, Marjoram, and Rosemary, can be used to extract these oils (Yepez et al, 2002).

Camphoraceous oils

These essential oils are specifically therapeutic in nature. Some of these essential oils come from plants like Cajeput, Boreol, and Tea Tree, which has a flavour reminiscent of baked plums and mugwort. (Weyerstah et al, 1993).

Floral oils

This category includes oils that are manufactured from floral components or that contain plant-derived floral essence. Plants that generate these oils include jasmine, geranium, rose, neroli, ylang-ylang, chamomile, lavender, etc. (Paulo et al, 1998).

Woody oils

Essential oils with a woody scent or those that are derived from the bark and other woody plant parts. Such oils are produced by cedar wood, cinnamon, juniper berries, cypress, pine, and other plants (Junming et al, 2010).

Earthy Oils

Essential oils that are either extracted from the roots and other earthy portions of vegetation or possess a distinctly earthy scent. Some of these oils are produced by Valerian, Angelica, Vetiver, and Patchouli (Jirovetz et al, 2002).

Spicy oils

Spices and hot plants including thyme, aniseed, cloves, black pepper, cardamom, coriander, cinnamon, ginger, cumin, and nutmeg are used to make oils (López-Cortés et al, 2013).

Essential oil extraction methods

Steam distillation

As per the study of Machado et al. (2022), the typical method for separating volatile compounds from plant material to produce essential oils is distillation. During the distillation process, essential oils from aromatic plants are released by evaporation when they are exposed to steam or boiling water. The idea that while distilling two unmixable liquids, especially essential oil and water, the aggregate vapour pressures equal ambient pressure at boiling temperature facilitates the recovery of the essential oil.

The length of the distillation process, pressure, temperature, and most crucially, the nature and quality of the organic material affect the quantity of essential oil during production. From 0.005 to 10% of plants are routinely extracted for their essential oils. Water-steam distillation, water distillation, and steam distillation are the three evaporation techniques that have historically been used. Water distillation is also referred to as “indirect” steam distillation. Plant material is boiled after being soaked in water during this process. The volatile oils are carried by the steam created when water is brought to a boil. After that, cooling and humidification are used to separate the oil from the water. In addition to being sluggish, this approach has the problem that heat causes materials and smells to degrade over time. The leafy plant material is held on a grill over the hot water in the steam method, and the steam travels through the plant material. The leaves must be positioned carefully on the grill to provide even heating and complete extraction. “Direct” steam distillation is the technique most usually employed to extract essential oils. The high temperatures and prolonged isolation durations may change the chemical composition of the crude oil components, typically leading to the loss of the most volatile compounds. After the vapour is piped away and condensed, a mixture of liquid oils is created. The oil has a burnt, smokey scent as a result of some plant material elements breaking down (pyrolyzing) as a result of the high temperatures used.

Padilla-de la Rosa et al, 2021 described the process of steam distillation as: In order to obtain a residual flow, the juice flow is fed (F), passing sequentially through each of the five stages (W). The resulting steam (V) is then condensed in each stage’s condenser to produce the distillate stream (D), which is then used to separate the distilled oil by decantation for a subsequent physicochemical and chromatographic analysis. The feed (F) in the first stage of the apparatus receives the liquid to be distilled, which then passes through each of the five stages of the apparatus until it reaches the waste stream (W). The volatiles are evaporated in each of the processes using both heat exchangers, and then they are recovered in each of the five condensers to produce the distillate (D). This equipment contains a heat recovery system that enables the waste heat (W) from preheating the feed (F) to be recovered, which further reduces energy use when the sensible heat is recovered. A distilled fraction (D) is produced in each of the condensers and is later characterised. This fraction (D) can be blended to achieve the required profile or composition.

According to Packiyasothy and Kyle, (2002) hexane-extracted essential oils have higher antibacterial activity than the similar steam-distilled essential oils. According Bendahou et al. 2008, the content of oregano oil varies depending on the extraction technique used. Steam distillation is the most popular method for producing essential oils since it is simple to use and reasonably priced. This method is most usually used to produce essential oils. However, there are still several technologies that are not widely used, such as solvent extraction, microwave extraction, and hydro distillation. Supercritical carbon dioxide is a method that spares labile compounds from thermal and hydrolytic degradation. This approach also significantly reduces the process’s time and avoids the accumulation of potentially dangerous solvent residues. By extracting with liquid carbon dioxide at high pressure and moderate temperature, an expensive organoleptic character, a lot more natural product is created (Sánchez-González et al, 2011).

Hydro distillation

Conventional EO extraction methods like hydro distillation (HD) and organic solvent extraction often suffer from low productivity, high costs, and severe contamination. Modern technology and the green idea have led to the development of various unique approaches to solve the shortcomings of the conventional extraction strategy. Examples include hydrodistillation with enzyme assistance, hydro distillation with ultrasonic assistance, and hydrodistillation with a microwave (EAHD). According to the European Pharmacopeia’s instructions, an apparatus in the Clevenger type was used to extract the essential oil from A. malaccensis wood. Conventional EO extraction methods like hydro distillation (HD) and organic solvent extraction often suffer from low productivity, high costs, and severe contamination. Modern technology and the green idea have led to the development of various unique approaches to solve the shortcomings of the conventional extraction strategy. Examples include hydrodistillation with enzyme assistance, hydrodistillation with ultrasonic assistance, and hydrodistillation with a microwave (EAHD) (Chen et al, 2022a, b). To determine the yield of essential oils from fresh rue, the dry matter concentration was obtained prior to the separation procedure. The grinding operation is carried out in a food processor with a glass bowl to improve the separation of the oil from the cells of the different plant.

As per the study of (Sneha et al, 2022) 50 ml graduated burette was used to determine the volume of oil produced after the water vapor responsible for the lavender oil was concentrated and eluted. This produces two phases: an aqueous supernatant and an oily precipitate. A Pasteur pipette was used to collect the oily phase. Traditional techniques for obtaining bioactive chemicals from plants include hydro distillation. This process involves packing plant materials into a compartment that is motionless, adding just enough water, and then bringing it to a boil. As a substitute, direct steam might be injected into the plant sample. The oil and water vapour mixture is indirectly chilled with water to get it to condense. As the compressed solution is transferred from the condenser to the separator, the bioactive compounds and oil are separated from the water automatically. Despite its many advantages, including the lack of organic solvents in the procedure, the elimination of the need to dry the plant materials, and quicker extraction periods, the usage of phenolic compounds, which are heat-sensitive, is constrained in high-temperature applications (Zhang et al, 2022a, b).

Hydro diffusion

The separation of essential oils from plant materials involves hydro diffusion, hydro distillation, and steam. Indirect (dry) steam is used in the distillation of steam. Hydro distillations are characterized by the heating of the plant matter with water and the production of steam inside the still. Low-pressure steam (0.1 bar) is used for hydro diffusion, and osmotic action replaces the volatiles from the intact plant material.

The osmotic impact of steam and water on plant cells is the fundamental basis of hydro diffusion. Koeda Metal demonstrated that the rate of diffusion of the different constituents through the cell membranes, which in turn is determined by the degree of solubility of the compounds in the distillation water, governs the amount of evaporation of the volatile constituents during (hydro) distillation from uncomminuted plant matter. This sort of diffusion was initially recognized and named by Von Rechenberg as “Hydro diffusion” section. Due to the apparatus’s design, the low-pressure steam flow in the Schmidt hydro diffusor flows from the top through the vegetable load down to evaporate at the bottom by the law of gravity. This slow-acting process takes less time than hydro distillation. 25–50% of the time and energy (steam) can be conserved with the hydro diffusor. The distillate water cannot be recycled, thus eventually the water layers must be removed using the proper equipment (Fig. 2). Additionally, the yields of essential oils obtained through hydro diffusion should be equal to or higher than those achieved through hydro distillation. The separation of oils from the condensate in the hydro diffusion process in Florentine flasks is inefficient in our studies since the yields of hydro diffusion and hydro distillation were more or less identical. The sorption sequence of the volatile components is dictated to a great extent by their water solubilities during the hydro diffusion of oils from intact (uncommunicated) primordial materials, and as a result, the condensed water is more or less flammable.

Fig. 2.

Hydro diffusion methodology

Hydro distillation

It will become obvious that the ease with which plant cells release oils determines how easy it is to isolate a certain oil. Essential oils may be found in isolated cells, such as organelles or idioblasts (as in the Lauraceae and Rutaceae families of plants), or more prominently at the interface of the plant material, such as in glandular hairs (as in the leaflets of the Labiatae family), cavities, ducts, or canals (like in UmbelIiferous fruits). Steam distillation of essential oils from herbs has well-known thermodynamic effects. However, the hydrodistillation and hydro diffusion processes used to extract essential oils from organic material are more difficult. From the substance’s inside to its exterior, the oil must disperse. Additionally, non-volatiles like lipids (fatty oils), which hold onto the volatile components, are also present in plant tissue. Thus, the partition coefficients, diffusion rates, water solubilities, partial vapor pressures, durations, and velocities of heat transfer all play a part in the steam-based isolation of volatiles from plant material. When Koedametd. “Compared to the isolation processes for essential oils”, they discovered that the order in which the volatile components are isolated during the hydro distillation of oils from specific plant material is mostly influenced by their water solubilities rather than their boiling points. This phenomenon was explained by the fact that hydrodistillation was not as effective in isolating the components as hydro diffusion, which is connected to water solubilities (Related to partial vapor pressures, e.g, boilingpoints).

Solvent extraction

Based on the raw material status, solvent extraction might be referred to as liquid–liquid or solid–liquid extraction (Ignat et al, 2011). Leaching, also known as solid–liquid extraction or phenolic extraction, is quite popular and straightforward techniques. A molecule is extracted from one solvent into another during this process because the solubility or distribution coefficient of these two immiscible (or scarcely soluble) solvents differs. When compared to other separation methods, it offers a better separation effect than chemical precipitation, a higher degree of selectivity, and a quicker mass transfer than the ion exchange method. In comparison to distillation, solvent extraction provides benefits such as minimal energy consumption, large production capacity, swift action, straightforward continuous operation, and ease of automation. Several cutting-edge separation approaches have been developed in recent years to adapt to the expansion of DNA restriction and genetic editing techniques. These techniques include the extraction of membrane separation, reverse micelles, and supercritical fluid.

The procedure involves utilizing an appropriate solvent to directly extract fresh or freeze-dried plant material using an extractor, homogenizer, or ultrasonic bath for a specific amount of time. The multi-phase, unstable state mass transfer procedure is used in solid–liquid extraction. Throughout the extraction, the solute and solid’s concentrations are continuously changing. The mass transport phenomena may be amplified by modifications to diffusion coefficients, boundary layers, or concentration gradients. During the liquid–liquid extraction procedure, an initial liquid solution (raw material) containing one or more solutes is thoroughly combined with an immiscible or almost insoluble liquid (solvent) (Ignat et al, 2011). Maceration, the simplest solvent extraction technique, is popular and cost-effective for the extraction of bioactive compounds. The pre-treatment samples are held in a closed jar with an appropriate solvent while they are dried and/or ground. The solid portion is then compressed to recover significant amounts of occluded solutions after the liquid has been strained off. To get rid of the contaminants, the liquids are blended and filtered. Most of the time, shaking is used to enhance the extraction process in two ways: Increasing diffusion and removing concentrated solution from the sample surface will boost the extraction yield by bringing new solvent in contact with the sample (Azmir et al, 2013). The developing extraction methods have been compared to maceration, which has been proposed to be more adaptable, practical, and affordable for small and medium-sized businesses (SMEs) (Vongsak et al, 2013). By encouraging diffusion and providing fresh solvent volumes to the sample surface, periodic shaking during maceration speeds up recovery (Hogervorst et al, 2017).

Subcritical liquid extraction

A technique that produces essential oils with a increased yield and outstanding quality, preserves the majority of their value-added constituents and changes the least after the process of extraction is highly desired. Although chemical-free procedures are viable, they need a long processing time, and the yield and quality are frequently subpar. Subcritical water technology is used in this work to address these problems. In this project, subcritical conditions were used to extract essential oil from Aquilaria malaccensis wood, which was then analysed using gas chromatography/mass spectrometry (GC/MS). The temperature was shown to be the most important element in surface response optimization, and the ideal temperature, extraction time, sample-to-solvent ratio for subcritical water were found to be 225 °C, 0.2 gr/mL, and 17 min, respectively. The two simultaneous processes used in the subcritical water extraction technique are well-fit to the two-site kinetic and second-order models. The quality of the wood oils produced by A. malaccensis using the sub-critical water methodology are considerably better than those produced using the hydro distillation method, according to GC/MS results. These oils also contain some beneficial compounds with added value, such as furfural and guaiacol, which are useful in the creation of pesticide residues and medications. Pore size, functional group, and morphological examination showed that there had been significant damage to the samples, which aided in the extraction of bioproducts more effectively. The utilization of the subcritical approach results in greater oil production and quality than conventional methods while taking less time to process.

Solvent-free microwave extraction

Solvent-free microwave extraction (SFME) was developed in 2004 by Chemat et al. This process, which has a very simple underlying idea, involves using a microwave to dry distil a fresh plant matrix without the need of water or any other organic solvent. A modified hydro-distillation (HD), which utilises a lot of water, and a modified microwave-assisted extraction (MAE), which employs organic solvents, are not the same as SFME. As a result of the selective heating of the in-situ water content of plant material, the glands and oleiferous receptacles explode. As a result, by using azeotropic distillation and water, the essential oil is released from the plant material. The additional water can be refluxed into the extraction vessel in order to reintroduce the original water to the plant matter (Fig. 3). Citrus fruits, fragrant herbs like basil, mint, and thyme, as well as spices like ajowan, cumin, and star anise have all been treated with this technique (Filly et al, 2014).

Fig. 3.

Solvent—free extraction microwave method

Properties of essential oils

Antibacterial

Certain nutritional factors (fats, proteins, salt, carbohydrates, antioxidants, water, preservatives, and other additives) and pH may reduce the biocompatibility of EOs; in addition, some extrinsic factors (Packaging in vacuum/gas/air, temperature, and microorganism features) are important. Numerous studies found increased levels of bioactivity at acidic pH because EOs behave more hydrophobically and can enter cells more readily at negative pH. Large levels of lipids, proteins, and/or water in food may function as a barrier against bacteria and absorb EOs, reducing their concentration and potency in the aqueous phase. On the contrary hand, high levels of salt and/or water may help EOs work more effectively. Researchers looked into the impact of food items such as potato starch, beef extract, sunflower oil, and pH (4–7) on the antibacterial activity of oregano and thyme. They concentrated on L. monocytogenes’ lag phase as well as its maximal specific rate of growth.

The physical makeup of food may restrict and influence the biological activity of EOs. For instance, Salmonella Typhimurium was injected into both a gelatine gel and a broth, both of which contained an EO. Due to the limited dispersion of EO in the gel, its action was diminished. They mixed oregano with basil, thyme, or marjoram to target Escherichia coli and Pseudomonas aeruginosa, and these mixtures often demonstrated considerable consequences. Due to the high volatility of EO active chemicals, their presence in gaseous form makes it easier for lipophilic monoterpenes to dissolve in cell membranes. According to Tyagi et al. (2012, 2013), who evaluated lemon grass and menthol oils in conjunction with light heat therapy (55 °C), other articles concentrated on the use of EOs in combinations with other therapies. Since the amount of oil in the vapor phase increases as temperature increases, this technique considerably decreases the volume of oil that is needed while also enhancing the antibacterial action of the oil.

Antifungal

In particular, persistent cutaneous, nail, or mucosal infections that can be serious in elderly or immune-compromised people, fungi are becoming more and more significant sources of deep-seated human illnesses that are persistent or acute (Cavaleiro et al, 2006). On the other hand, a number of fruit, cereal, and other Crops can become contaminated by fungi during preservation or in the environment. Regulations limiting undesired biocide residues must be followed by growers, who must also select treatments that will preserve the goods’ quality. However, there is growing worry about the health dangers brought on by fungi and their spores in environments where people live (Prusky et al, 2007). So, inhibiting fungal development is a good strategy to stop the buildup of mycotoxins. It is crucial to remember that mycotoxin formation may increase as a result of partial fungal growth inhibition, such as a drop in fungal growth rate. Crops of grains, vegetables, and fruits can become contaminated by fungi, primarily Aspergillus and Fusarium, then Penicillium, and other phytopathogenic species (Magro et al, 2006).

Aflatoxin toxins, which are the most prevalent Aspergillus toxins and are highly carcinogenic to both humans and many animal species; When present in high doses, the strong mycotoxin cyclopiazonic acid causes localised necrosis in the majority of the interior organs of vertebrates; The metabolite cytochalasin E is extremely poisonous; Strongly immunosuppressive gliotoxin is likely exclusively found in animal diets; Both ochratoxin A and sterigmatocystin are possibly carcinogenic to humans. Butenolide, a toxin produced by fusarium, has been linked to illnesses in cattle; Low toxicity describes culmorin; Fumonisins are extremely poisonous substances. Citrinin, a nephorotoxin, Mycophenolic acid, which can range in toxicity from low to acute, and other penicillium toxins Prokaryotes and eukaryotes are very poisonous to patulin, which also causes mycotoxicosis in animals. Rubratoxin is a strong hepatotoxin. Germination and hyphal extension are steps in the fungal growth process that lead to the formation of visible mycelium. Shortly after spores germinate, a product will spoil. In order to halt fungal growth, subsequent degradation, and potential mycotoxin generation, germination must be prevented. By using items that inactivate spores, it may also be extremely reducing the initial load of live spores is preferable. We must comprehend the conidia generation process in order to comprehend the process of fungal propagation. Conidia are cellular propagules that frequently form from aerial hyphae in areas that are behind the colony border and no longer contribute to vegetative growth. They serve as a way of dissemination for the fungus colony in a setting that is constantly changing. As a result, conidial production (conidiation) frequently rely on simple cellular modifications that can be completed in every aerial hypha extremely fast, leading to a coordinated and massive creation of spores. Conidiation has drawn interest in the food industry because conidia can be used as a biotransformation catalyst and as an inoculum for fermentations. Mycotoxins are well recognised to be present in fungus spores. Since the fungal spore is in its resting phase, antifungal substances do not readily react with it. It is very challenging to kill spores using techniques other than heat; spore germination happens gradually from resistant and non-responsive forms through a number of phases. To assess an antifungal compound’s effectiveness on fungal spores, one must be aware of how sensitive each stage is to it. Mycotoxins and toxic fungi can pose a risk to both human and animal health when they are present in foods and grains that have been kept in storage for a long time. To synthesize new pesticides for the management of fungus and pests without causing fungicide/pesticide pollution, there should be the development of some alternative native biodegradable chemical control methods. The non-phytotoxic, systemic, easily biodegradable, and stimulatory properties of EOs have led to a recent rise in interest in them throughout the world. Additionally, it may be able to use EOs to successfully combat the development of mycotoxin. It is important to look into each situation separately since the microorganisms (namely moulds) that come into contact with plant extracts or EO’s may promote the formation of secondary metabolites. EO’s demonstrated significant antifungal effects. It is impossible to link the partial inhibition of fungal growth with the inhibition of mycotoxin synthesis because fungistatic action may stimulate secondary metabolism in response to stress (Reyes-Jurado et al, 2015).

Antioxidant

The chemical makeup of EOs largely determines their antioxidant capacity. The significant antioxidant activity of EOs is due to the double-bond binding of phenolic and other secondary metabolites. Traditional species including Mentha longifolia, Galagania fragrantissima, Achillea filipendulina, Anethum graveolens, Hyssopusseravschanicus, A. rutifolia and Ziziphorac linopodioides are excellent sources of oxygenated monoterpenes such aldehydes, ketones, and esters. The primary chemical constituents that produce the strongest antioxidant activity are monoterpene hydrocarbons (A. absinthium and A. scoparia) and phenolic terpenoids, such as thymol or carvacrol (O. tyttanthum and Mentha longifolia). Important monoterpenes like thymol and carvacrol can be found in several EOs made from plants like O. tyttanthum, Mentha longifolia, and Thymus serpyllus (Caldefie‐Chézet, 2006). Attributed to the prevalence of important elements like thymol and carvacrol, the oils derived from medicinal herbs like cinnamon, nutmeg, clove, basil, parsley, oregano, and thyme have considerable antioxidant properties. Their primary functions are influenced by the presence of phenolic compounds, which have strong redox characteristics and are crucial for the neutralisation of free radicals and the breakdown of peroxide (Burt, 2004). Linalool, 1,8-cineole, geraniol/neral, citronellal, isomenthone, menthone, and certain monoterpenes are only a few of the additional ingredients that play a significant part in the antioxidant effects of EOs (Bhavaniramya et al, 2019).

Terpenolic and phenolic chemicals found in essential oils have antioxidant action. Most in vitro research on the antioxidant activity of EO has used physico-chemical techniques. Table 1 lists a few EOs along with the tests that were performed to measure their antioxidant activity. For instance, few researchers used three complementary assay procedures to assess the free radical scavenging abilities of a compound: attenuation of ABTS⁺ radical generation, a horseradish peroxide/perborate/luminol combination inhibits iodophenol-enhanced chemiluminescence and shields a target enzyme from oxidative degradation. OH or O₂⁻ produced by cinnamon, pimento, and bay essential oils, which have potent antioxidant properties. None of the studied plant extracts exhibit any appreciable antioxidant protection against OH or O₂⁻ species. Citrus oils, such as bergamot or lemon, have very little antioxidant action. Other publications employ the DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) assay to assess antioxidant capability; this approach is predicated on the antioxidant scavenging the stable DPPH radical. The method employed affects the determination of the antioxidant activity. The methodology and the specific free radical species generated are the only factors that affect the apparent antioxidant activity of free radical scavenging treatments. Therefore, it would appear crucial to assess antioxidant activity using a variety of techniques. According to earlier research, several essential oils show strong antioxidant effects on par with butylated hydroxytoluene, a well-known antioxidant (BHT) (Sánchez-González et al, 2011).

Table 1.

Effect of different essential oils on microorganisms and their medical applications

Essential oil	Classification	Microorganism	Medicinal Applications	Food matrix	References
Limonene Eucalyptus oil Eugenol Peppermint oil Tea tree oil Clove oil Cinnamaldehyde Carvacrol Thyme oil	Gram positive bacteria	Brochotrix thermos pacta Staphylococcus delbrueckii Listeria innocua	Colagogue, hepatoprotective, antioxidant, anti-inflammatory, antifungal, antimicrobial, and anthelmintic activities	Semi-skimmed UHT milk	Bora et al. (2020)
Carvacrol Cinnamaldehyde Clove oil Limonene Eugenol Lemongrass Tea tree oil Thyme oil	Gram negative bacteria	Escherichia coli Salmonella enteritidis Staphylococcus aureus Listeria monocytogenes	Antimicrobial activities antifungal, ant aflatoxin, antioxidant, and phytotoxic activities	Tzatziki (cucumber and yogurt salad) Taramasalata (fish roe salad) and pate	Chen et al. (2021)
Eugenol Tea tree oil Limonene Cinnamaldehyde Carvacrol	Fungi	Zygosaccharomyces bailii Saccharomyces cerevisiae Fusarium oxysporum Aspergillus niger Aspergillus ochraceus Trichoderma viride Penicillium funiculosum Penicillium ochrochloron Penicillium aurantiogriseum	Antibacterial, antifungal, anticancer and antiprotozoal activities	Wheat Chickpea	Bhavaniramya et al. (2019)
Peumus boldus Artemisia scoparia Ajowan (Trachyspermum ammi)	Plant family-Monimiaceae Ranunculaceae Apiaceae	Staphylococcus aureus Listeria monocytogenes Listeria innocua	Antioxidant and radical scavenging activity Antimicrobial, antioxidant, ant aflatoxigenic, and antisemitic activities	Dry fruits	Majeed et al. (2015)
Nigella sativa Citrus	Plant family-Ranunculaceae Cyperaceae	Fusarium oxysporum Aspergillus niger Aspergillus ochraceus	Anti-inflammatory, anti-arthritic, analgesic and anticonvulsant activities	UHT milk	Hanif et al. (2019)
Peppermint Cyperus esculentus and Cyperus rotundus	Plant family-Lamiaceae Rutaceae	Brochotrix thermos pacta Staphylococcus delbrueckii	Antioxidant, antimicrobial, and anti-inflammatory activities	Full fat and low fat soft cheeses	Diniz et al. (2020)
Spearmint Caraway Rose citronella	Plant family-Lamiaceae Apiaceae Rosaceae Cardiopteridaceae	Aspergillus ochraceus Trichoderma viride Penicillium funiculosum Penicillium ochrochloron Penicillium aurantiogriseum	Aromatherapy and complementary medicine Antiseptic, antibacterial, antifungal, and anaesthetic activities	Eggplant salad Fruit juices	Chen et al. (2021)

Anti-cancer

According to the International Agency for Research on Cancer, there were 8.2 million cancer deaths and 14.1 million new cancer diagnoses globally in 2012 (IARC). The majority of cancer-related deaths occur from lung, liver, stomach, colorectal, breast, prostate, and oesophageal cancers. Cancer is currently the leading cause of death and is expected to increase by 70% over the next two decades. There is an impending need for innovative and new chemotherapy treatments (Fig. 4). Generally speaking, there are three phases of cancer: (1) start, in which carcinogen exposure and defective DNA repair processes result in cellular DNA damage and mutation (2) advancement, where hyperproliferation, tissue remodelling, and inflammatory happen as a result of the development of initiated cell(s); and (3) progression, where preneoplastic cells grow clonally to form tumours, which is additionally aided by an increase in genomic instability and altered gene expression. Due to the progression of cancer, which results in changes in susceptibility to therapy, the various stages of carcinogenesis call for various chemotherapeutic techniques. Through the accumulation of variants for genes involved in cell proliferation, apoptosis, and DNA repair, among other things, tumour growth is specifically linked to genomic instability. Chemotherapy medications influence the promotion stage by inhibiting cellular proliferation, speeding up cell death, and inducing tumour cell specialization, among other mechanisms (Blowman et al, 2018).

Fig. 4.

Schematic representation of anticancer activity of essential oils

Although research on the use of EOs as anticancer therapeutic agents is still in its infancy, it is estimated that 50% of conventional chemotherapeutic drugs are derived from plants, with 25% of them coming from plants directly and 25% from chemically altered phytoproducts.

The chemical paclitaxel is one example. The bark of the tree Taxus brevifolia was first used to make paclitaxel, whose most popular brand name is Taxol. Its mode of action relies on the targeting of the cytoskeleton’s tubulin, which induces a mitotic arrest, activates the mitotic checkpoint, and then induces apoptosis (Weaver et al, 2014). It is utilised as a therapeutic agent for a variety of cancer types, including ovarian, breast, and pancreatic cancer, either as a single agent or in common therapeutic schemes. Due to the decrease of the natural supply, this medication has to be synthesised in a lab, principally using the EO ingredient patchoulol to make patchoulol oxide. Recently, Altshuler and associates discovered that (+)-citronellal, a key component of Corymbia citriodora and Cymbopogon nardus essential oils, is also a potent microtubule-disrupting substance, much like the more well-known microtubule-disrupting drugs vinblastine and colchicine (Altshuler et al, 2013).

Potential applications and advantages of EOs in the food sector

Essential oils are abundant in bioactive chemicals, have some exceptional antioxidant and antibacterial activity, and have been classified as Generally Recognized as Safe (GRAS) by the USFDA. These attributes make them appealing as food preservatives (Atarés et al, 2016). However, because of their strong antibacterial and antioxidant qualities, the use of essential oils as food additives has recently gained more attention. These essential oils differ from one another in terms of their biological activity, physical–chemical makeup, and scent. Therefore, it’s crucial to choose the best option or combination for each application (Chen et al, 2021). The very useful plant extracts known as cinnamon essential oils which are employed in the food and cosmetic sectors, particularly as an antibacterial ingredient. Essential oil of cinnamon combined with cyclodextrin nanosponges can produce antibacterial food packaging (Simionato et al, 2019). Garlic essential oils have been shown by numerous researchers to have potent antibacterial action against foodborne microorganisms (Dghais et al, 2023). The food industry has maximized this beneficial property to use it as a potent preservative or to apply it to packaging. Vegetables, meat, fish, rice, fruits, and dairy products are just a few examples of the wide range of food items that essential oils and their constituents can protect from spoilage and fight pathogens in. (Nazari et al, 2019). Various applications of essential oils have been explored in the food industry like, Clove, Cinnamon and Cardamom essential oils hinder the formation of yoghurt starting culture more than mint oil. In another trial, mint oil has proven to be beneficial against Salmonella enteritis in low-fat Greek yogurt and vegetable salad (Vazquez et al, 2023). Due to the low amount of fat of the products, the use of herbal extracts in washing water has a better impact against organic spoilage microbes and food-borne pathogens in vegetables. In rice, sage oil and carvacrol demonstrated a considerable antibacterial activity against Bacillus cereus (Kaewpetch et al, 2023). In the case of fruits, the effectiveness of EOs may be influenced by the pH levels of the fruit and vegetables (Moustafa et al, 2023). The antimicrobial activity of essential oils in chocolate was also evaluated at different temperatures, under dry and umidified environment, and it has been revealed that lemon flavour applied to chocolate infested with E. coli had shown the strongest inhibitory action. Antibacterial activity of essential oil was reduced in the food system, as revealed when it was mixed with chocolate (Wang et al, 2023). Because of their strong antibacterial action, essential oils have been employed in the formulation of antimicrobial food packaging and edible films. Incorporating antimicrobial agents into edible films is an innovative method of improving the safety and storage stability of ready-to-eat foods. Bioactive functions of various essential oils are given in Table 2.

Table 2.

Bioactive functions of various essential oils

Essential oil	Film	Packaging	Food	Active Function	Preservation	Main results	References
Oregano	Whey protein isolate (WPI)	Gelatin edible film Chitosan and hydroxypropylmethyl cellulose edible films	Fresh beef	Antimicrobial	Antibacterial activity against Escherichia coli, Listeria monocytogenes and Staphylococcus aureus	Double the shelf-life of fresh beef stored under refrigerated conditions	Akram et al. (2019)
Clove	Sunflower protein concentrate	Chitosan and locust bean gum edible film	Sardine patties	Antimicrobial Antioxidant	Effective against Aspergillus flavus in dates	Slowed their lipidic auto-oxidation Slightly delay the growth of total mesophiles	Vianna et al. (2021)
Winter savoury Cinnamon Oregano	Alginate	Gelatin edible films	Bologna and ham	Antimicrobial	Protect oranges from Penicillium italicum	Higher migration of active compounds	Atares et al, (2016), Ribeiro et al. (2017)
Cinnamon Clove	Cassava starch	Nanoemulsion coating	Bakery	Antimicrobial	Chitosan film combined with lemon, thyme and cinnamon essential oils provide a new formulation for antimicrobial films	Effective against the fungal tested was high and it became impossible to obtain films Antimicrobial activity and It can be applied in bakery	Zhang et al. (2022a, b)
Oregano	Cellulosic resin	Chitosan based edible coating	Pizza	Antimicrobial	Increases antimicrobial activity and prolongs the shelf life of vegetable products	Inhibition against Penicillium spp, and Staphylococcus aureus	Souza et al. (2021)
Oregano pimento	Milk protein	Novel edible coating with modified chitosan Gum based edible coating	Whole Beef Muscle	Antioxidant Antimicrobial	Effective in preventing microbial growth and lipid oxidation in silvery pomfret and shows the potential to preserve seafoods	Effective antimicrobial activity Highest antioxidant	Varghese et al. (2020)

Essential oils are incredibly useful for applications involving food safety, food preservation, and packaging. Gelatin and essential oils can be used to create films that have better physicochemical properties as well as antibacterial action. Chitosan’s benefits can be enhanced further when the essential oil is applied. Research classified the potential of edible gelatin covering with the effect of adding orange leaf essential oil lengthens the shelf life of chilled pink shrimp. It was demonstrated that coating shrimp with 2% orange leaf essential oil increased their shelf life by 10 days when compared to untreated samples. In a few studies, scientists have used essential oil of orange peel in chitosan to examine the shelf life. Pink shrimp were used in this study. To inhibit lipid oxidation and microbiological development, 2% orange peel essential oil was added to chitosan, extending the shelf life of shrimp by nearly 8 days compared to uncoated shrimp. A study by Randazzo et al. (2016) calculated the antibacterial properties of 8 essential oils extracted from the peel of orange, lemon, and mandarin. He used these oils to analyze 76 L. monocytogenes bacterial strains. When combined with methylcellulose- or chitosan-based biodegradable films, the essential oils’ potential antibacterial effect was shown to be most inhibited. Chiabrando and Giacalone (2019) used the shelf-life of fresh-cut Jintao kiwifruit pieces to examine the effects of an edible coating comprised of sodium alginate combined with grape, orange, and lemon essential oils.

Food goods need to be protected against environmental variables such as UV light, oxygen, water vapor, pressure, and heat. Defending against chemical and microbiological pollutants also contributes to improving food safety and extending shelf life. Numerous packaging technologies support preserving food quality. Due to their favourable effects on resolving environmental issues and raising consumer acceptability, more innovative techniques, such as active packaging, surpassing more established packaging technologies. Due to their capacity to operate as oxygen scavengers and permit the diffusion of active substances into coated food products, essential oils boost the antioxidant activity of the packaging materials. Since essential oils are rich in bioactive chemicals, they enhance the packaging material’s antibacterial qualities, which in turn shield food from harmful microorganisms (Pandey et al, 2022).

As seen in this review, there are several scientific interests in studying the characteristics, uses, and essential oils compositions as well as the many extraction techniques. To determine the smallest amount that can prevent the expansion of microbes or guarantee their antibacterial or antifungal properties, taking into account their application via direct or indirect techniques, the antimicrobial activity of essential oils from various plants and spices has been investigated. Despite extensive research on the application of these essential oils in the food, drug, and cosmetic sectors, the extraction of these natural oil production continues to be a bottleneck. This is because novel essential oil extraction procedures have been developed as a result of the conventional essential oil extraction methods’ low yields and/or lengthy extraction timeframes. Process simulation mathematical models have also been presented to optimize both conventional and novel extraction techniques. These models enable the virtual evaluation of various processing conditions for essential oil extraction before they are carried out at a scale in a lab or pilot plant. Essential oils have a wide range of potential applications as antimicrobial agents, and the research from this review suggests that they may eventually replace traditional antimicrobials.

Declarations

Conflict of interest

The authors have no conflicts of interest to declare.