**4. Extract**

The residual biomass from the distillation of aromatic plants to obtain essential oils contains valuable components such as carotenoids, carbohydrates, lipids, flavonoids, and phenolic acids within a lignocellulosic matrix. The current destiny of most distillation residues is a garbage dump. When this is not the case, common applications are the transformation into biofuel (as raw lignocellulosic bagasse, or with further processing into biochar) or as a major ingredient for composting operations. However, an important and profitable step may be inserted before these treatments to take advantage of the presence of flavonoids and other bioactive molecules in these residues. Extraction techniques may be employed to obtain fractions enriched in these bioactive substances. Maceration, Soxhlet extraction, microwave-assisted extraction, ultrasonic-assisted extraction, supercritical extraction techniques, pulse electric field extraction, enzyme-assisted extraction, molecular distillation, and accelerated solvent extraction are some of the tools employed to obtain extracts from plant materials. Further processing may involve ultrafiltration, nanofiltration, membrane filtration, supercritical antisolvent fractionation, or other physical processes that help to separate extract components according to molecular size. Rosemary (*Salvia rosmarinus*) is a medicinal and aromatic herb that contains bioactive compounds (carnosic acid, carnosol, rosmarinic acid) of interest in many fields. Many of the previously mentioned techniques have been applied to fresh and residual rosemary biomass and this collective effort permits the comparison of these techniques and their operating conditions according to yield, extract stability, costs, and energy demands [13].

The efficient recovery of bioactive compounds from the distillation residual biomass is an important subject of current research in the field of aromatic plants. A search of scientific publications from 2000 to July 2023 on "aromatic plant" in Scopus produced 28,973 results, more than 25% of which (6556) included the word "waste." Many works have determined the compositions of extracts obtained from the biowaste of individual aromatic species at the laboratory scale with various techniques. Polyphenols are frequent constituents, and their presence is related to the antioxidant

#### *Essential Oils and the Circular Bioeconomy DOI: http://dx.doi.org/10.5772/intechopen.112958*

or antimicrobial activities determined for the extracts. It is now clear that the solid wastes from essential oil distillation are rich sources of bioactive molecules with applications in the cosmetic, food, pharmaceutical, hygiene, and other industries. The challenges are scaling up the extraction processes and developing extract fractionation processes toward enrichment in specific sets of compounds or isolating individual substances. The following are examples of the general situation of the addition of value to aromatic plant distillation waste through the production of extracts.

The term "polyphenols" designates phenolic substances that contain several hydroxyl groups but does not imply that they have a polymeric nature. A more general denomination is "phenolic compounds." They include hydroxybenzoic acids, hydroxycinnamic acids, phenylpropanoids, coumarins, flavonoids, and phenolic terpenes [14].

*Rosa alba* waste from steam distillation and supercritical CO2-extracted fresh flowers and steam distillation wastes from *L. angustifolia*, *M. officinalis*, and *Ocimum basilicum* essential oil production were dried at 50°C, ground, sieved (0.5 mm), and macerated with 70% ethanol (1:6 w/v) at 60°C (1 h) and room temperature (24 h). The CO2-extracted *Rosa alba* afforded the extract with the highest polyphenol content (11 g/L), followed by melissa waste (6.6 g/L). Flavonoids such as rutin (1.2 g/L), catechin (1.1 g/L), and quercetin-3-glucoside (0.7 g/L) were quantified in these extracts using HPLC-DAD. Basil waste produced the extract with the highest rosmarinic acid content (1.2 g/L). Other phenolic acids, such as gallic, ferulic, and 3,4-dihydroxybenzoic acids, were found in the extracts at concentrations between 0.1 and 0.6 g/L. Thus, the distillation wastes from these aromatic plants are a rich source of polyphenols that could be used as supplements to increase antioxidant activities in food [15].

Ultrasonic agitation (37 kHz, 30°C) and 70% methanol were used to obtain extracts from residual distillation biomass of six aromatic species (*M. officinalis*, *Mentha spicata*, *Origanum vulgare*, *Salvia fruticosa*, *S. rosmarinus*, and *Satureja thymbra*). LC-MS analysis of these extracts identified a total of 48 compounds, including 20 phenolic acids, 26 flavonoids, and 2 phenolic diterpenes. Phenolic acids varied from 3817 mg/100 g (*S. rosmarinus*) to 14,462 mg/100 g (*M. spicata*). Flavonoids varied from 747 mg/100 g (*S. fruticosa*) to 3112 mg/100 g (*Satureja thymbra*) [16]. Rosmarinic acid is a frequent component of residual biomass extracts, determined at concentrations between 0.7 and 154 mg/g of extract [17]. Its higher concentrations have been reported in residual biomass extracts of *M. officinalis* (93.3 mg/g), *M. spicata* (96.6 mg/g), and *Thymus vulgaris* (105 mg/g) [18].

Residual rosemary hydrodistillation biomass was dried, ground, and extracted with ethanol under ultrasonic agitation. LC-MS analysis showed that 60% of the chromatographic area was represented by carnosol (35.6%), carnosic acid (12.1%), cirsimaritin (9.1%), and genkwanin (4.7%). The absence of rosmarinic acid was attributed to its thermal degradation evidenced by the presence of caffeic acid (0.9%) in the extract, and at its dissolution in the hydrosol [19]. The antioxidant activity of this extract was high, similar to that of the extract obtained from red grape pomace. It had insect antifeeding effects on *Leptinotarsa decemlineata* Say (Coleoptera:Chrysomelidae) (polyphagous/olyphagous chewing insects) and the aphid *Myzuspersicae sulzer* (Hemiptera:Aphididae).

The unfractionated rosemary extract can be used as an antioxidant or as a natural crop protectant, among many other applications. However, there are continuous efforts to isolate its main components or to obtain enriched fractions. Increased yields of ursolic acid (15.8 mg/g), rosmarinic acid (15.4 mg/g), and oleanolic acid

(12.2 mg/g) were obtained in ultrasound-assisted extraction by varying the pH, ethanol%, temperature, and solvent:solid ratio [20].

Thyme (*T. vulgaris*) is a common aromatic plant used in the traditional medicine, pharmaceutical, and food industries [21]. Residual biomass from thyme distillation was macerated with 75% ethanol (1:10 w/v) at room temperature for 1 day. The extract was obtained with a 3.85% yield with a phenolic acid content of 62 mg of gallic acid equivalents per gram of dry extract. LC-MS analysis revealed that its main components were rosmarinic acid (105 mg/g) and rutin (87 mg/g) [18].

Culinary herbs of many cultures include some types of oregano, of which there are several species from various origins. Carvacrol and thymol are the most common oregano essential oil components and are also the main contributors to the bioactive properties of this herb. The variability in origin and habitat is reflected in the reported 20-fold variation in carvacrol content found in comparisons of essential oils obtained from different oregano species [22]. Mexican oregano is mainly represented by *Lippia graveolens*, whose essential oil is rich in thymol in carvacrol. The analogous species in northern South America is *Lippia origanoides*, which in Brazil is more commonly recognized as *Lippia sidoides*, a synonym according to genetic studies [23]. Similar to other species, there are many *L*. *origanoides* and *L. graveolens* chemotypes, which are distinct populations within the same species with different secondary metabolite profiles. There are reports of at least five *L. origanoides* chemotypes, some of which have no thymol or carvacrol in their essential oils [24, 25].

One approach to the complete utilization of *L*. *origanoides* categorizes essential oil and hydrosol as products of the distillation process and directs the residual plant material to various purposes, such as extraction, composting, or combustion material for steam generation. A patent has been granted for this process, specifically applied to *L*. *origanoides* [26].

Extraction with ethanol-modified supercritical CO2 of the residues from thymolrich *L*. *origanoides* distillation afforded a resin that contained 20 g of flavonoids/kg. When applied to the phellandrene-rich *L*. *origanoides* chemotype, oleoresin contained 31 g of valuable pinocembrin/kg [27]. This relatively large content of pinocembrin motivated further studies on solubility [28] in CO2, and mass transfer models [29]. A recent report of this work showed that the use of two coexisting fluid phases with various proportions of ethanol, water, and CO2, afforded an extract containing 145 g pinocembrin/kg, which is approximately a fivefold increase relative to the concentration obtained with ethanol-modified CO2 [30].
