Essential Oil Extraction Basics

Essential oils are hydrophobic secondary metabolites extracted from plants and commonly employed in perfumes, flavorings, and alternative medicinal practices like aromatherapy.

The primary method for extracting essential oils is through steam distillation. In this process, steam is generated in a separate boiler and then passed through botanical material in a still. This action softens the cells, enabling the essential oil to be released in vaporized form.

In the distillation of two dissimilar liquids, such as water and essential oil, each exerts its own vapor pressure as if the other were absent. When the combined vapor pressures equal the surrounding pressure, the mixture reaches a boiling point. Essential oil components, typically with boiling points up to 300°C, subsequently undergo evaporation.

After evaporation, the steam and essential oil undergo condensation and separation. Biomass steam distillation usually yields two products: a relatively pure essential oil and an aqueous condensate called a hydrosol. The essential oil consists of hydrophobic, often aromatic compounds produced in minimal concentrations as secondary metabolites in plants. Conversely, the hydrosol contains secondary metabolites that are more hydrophilic.
Essential Oil Extraction Basics

Leaching extraction process

Solid/liquid extraction is sometimes called leaching. When the soluble component is incorporated in a liquid, liquid/liquid extraction may be applied to recover the valuable soluble component.

Leaching process is influenced by processes such as desorption, complexation, and mineral dissolution. Commonly the extract is the product or intermediate product and the residue is a waste or byproduct.

Leaching is one of the oldest operations in chemical industries which involves the use of solvent to remove a solute form a solid mixture.

A solvent dissolves a solute, which is an element. As a result, the solvent will turn into a liquid, while the solute will be the component extracted from the solid matrix. Furthermore, in tea for example, the solute would be the extracted green tea, and the solvent would be hot water. In this example, the hot water removes substances from the solid matrix, i.e., the tea in the bag.

Leaching process is widely used in the biological and food processing industries for the separation of sugar from sugar beets with hot water, or for the extraction of oil from peanuts, soybeans, and sunflower seeds. Likewise, many pharmaceutical products are obtained by leaching plant roots, leaves and stems.

The advantages of leaching process include:
*Easy to execute.
*It is not very harmful when compared to pyrometallurgical methods.
*Does not generate any gaseous pollutants.
Leaching extraction process

Acid-Base Extraction

Extraction involves dissolving a compound or compounds either (1) from a solid into a solvent or (2) from a solution into another solvent. Acid-base extraction is the process of separating acids and bases in an organic mixture.

Acid-base extraction is typically used to separate organic compounds from each other based on their acid-base properties.

Generally, most organic compounds are neutral, and therefore more soluble in organic solvents than they are in water. However, if the organic compound becomes ionic, then it becomes more soluble in water. This is useful in extracting an organic acid or base compound from an organic phase to an aqueous phase.

An acid-base extraction can be used to extract carboxylic acids from the organic layer into the aqueous layer. Most organic carboxylic acids are insoluble or slightly soluble in water, but these compounds are highly soluble in dilute aqueous sodium hydroxide because the acid is deprotonated by the base producing the sodium carboxylate salt.
Acid-Base Extraction

Cold pressing method

Cold pressing is a method of mechanical extraction at room temperature (or lower than 140°F, 60°C), which involves crushing the seeds or nuts and forcing out the oil through pressure. The oil that can be consumed after precipitation and filtration without refining.

Cold press extraction is one of the methods required less energy than other oil extraction techniques and also environmental friendly.

Expression or cold pressing is commonly used in the production of essential and food oils. High quality oils can be obtained by performing production at low temperatures using cold press method. The term expression refers to any physical process in which the essential oil glands in the biomass are crushed or broken to release the oil.

Generally, the seeds are placed in a huge cylinder where they are continuously rotated and crushed until all the oil is collected.

The oil extraction rate of the cold pressed method is only half of the hot-pressed method. Hence, cold pressed oil is more expensive than hot pressed oil.

Cold-pressed oils are of higher quality because the temperature during the processing does not rise to a level that produces adverse effects on the ingredient. Cold pressed oil retains its natural flavor, color, bioactive substances, nutrients, and can be stored for a longer time without the use of additives.

Cold-pressed oils are suitable for food prepared in medium to low heat due to their low smoking points whereas hot-pressed oils are preferred for preparing meals at high temperatures due to their high smoking points.
Cold pressing method

Solvent extraction method

Extraction is a common technique used in organic chemistry to isolate a target compound. It is the first step to separate the desired natural products from the raw materials. In the extraction process, a solute is transferred from one phase to another to separate it from unreacted starting materials or impurities.

Extraction methods include solvent extraction, distillation method, pressing and sublimation according to the extraction principle.

Solvent extraction: The goal is to use a liquid (solvent) to dissolve (solvate) a target molecule or group of compounds (solute) and to wash them out of the solid plant material. The solvent is then separated from the solute in order to concentrate the solute. This separation is usually achieved by evaporating (distilling) the solvent, which concentrates the solute.

Solvent extraction is a method where chemical compounds are isolated based on their solubilities. Solvent extraction is the most widely used method. The main purpose of solvent extraction is to isolate hazardous materials from the sediments and sludge or separate the useful components from debris. The extraction of natural products progresses through the following stages:
1. The solvent penetrates into the solid matrix;
2. The solute dissolves in the solvents;
3. The solute is diffused out of the solid matrix;
4. The extracted solutes are collected.

The organic solvent selected should be such that:
*The given solid must be much more soluble in the organic solvent than in water.
*The extracting solvent must be immiscible with the solution to be extracted. Water or a water-based solution is usually one of the pair. The other solvent is an organic solvent. The extracting solvent should be sufficiently volatile so that it can be removed easily from the extracted material by distillation.

Volatile solvents such as hexane, benzene, ether, ethyl acetate, and dichloromethane are usually used for the extraction of semi-volatile compounds from water. Hexane is suitable for extraction of non-polar compounds such as aliphatic hydrocarbons, benzene is suitable for aromatic compounds, and ether and ethyl acetate are suitable for relatively polar compounds containing oxygen.

Method
The aqueous solution of the given solute is taken in a separating funnel. It is mixed with the desired organic solvent.

The funnel is closed, and its contents are shaken vigorously. It is then allowed to remain undisturbed for some time. Once the two phases settle back into two layers (in the funnel, the solvent forms the upper layer while the water forms the lower layer) they are separated by opening the stopcock at the bottom of the separatory funnel and allowing one layer to flow out. The liquid that had the solute removed is called the raffinate, while the liquid that gained the solute is called the extract. On evaporating the organic solvent, the solute can be recovered.

Solvent extraction has thousands of applications. It is used in many industries including the petrochemical, pharmaceutical, food, and beverage industries. It's also a common method used to separate and purify elements, proving this process a helpful way to recovery different chemical components.
Solvent extraction method

Soxhlet extraction

A Soxhlet extractor is a piece of laboratory apparatus designed in 1879 by Franz von Soxhlet. In the laboratory, soxhlet extractor is used for extraction. The soxhlet extractor uses the solvent reflux and siphon principle to continuously extract the solid matter by pure solvent, which saves the solvent extraction efficiency and high efficiency.

Soxhlet extraction is widely used for many types of solid samples, especially biological and environmental samples. It has been used for a wide range of samples like soils, sediments, and animal and plant tissues. A wide variety of solvents like dichloromethane (DCM), pure or mixed with acetone or hexane, and acetone–hexane mixtures can be used.

The soxhlet extractor setup consists of a round bottom flask, siphon tube, distillation path, expansion adapter, condenser, cooling water inlet, cooling water outlet, heat source and thimble.

In this method, sample needs to be crushed, using a pestle and mortar, to provide a greater surface area. The sample material is packed in filter paper and placed in the thimble which is placed inside the Soxhlet extractor.

The solvent is heated using heating source like isomantle and will begin to evaporate, moving through the apparatus to the condenser. Due to heat the solvent in the bottom flask vaporizes into the condenser. The condensate then drips into the reservoir containing the thimble. Once the level of solvent reaches the siphon it pours back into the flask and the cycle begins again.

The advantage of Soxhlet extraction is that it can be extracted multiple times. Compared with the general soaking method, it has the advantages of small solvent dosage, high efficiency and complete extraction.
Soxhlet extraction

Liquid-liquid extraction

Extraction method of compound in food:
*Liquid-liquid extraction (LLE)
*Solid-liquid extraction (SLE)
*Super-fluid (SFE)

Liquid-liquid extraction is a mass transfer operation in which a liquid solution (the feed) initially containing one or more solutes is thoroughly mixed with an immiscible or nearly immiscible liquid. It is a process carried out at room temperature and at atmospheric pressure.

This technique is used to extract aromatic compounds from a liquid. Since the liquid is usually aqueous, the solvent used is organic and immiscible in water to facilitate the separation of the two phases.

It is an extraction of substance from one liquid phase into another liquid phase. The solvent exhibits preferentially affinity or selectivity towards one or more of the components in the feed and has different density.

Extraction can be done in batch by certain an emulsion of the organic phase in the aqueous continuous phase, followed by phase separation to recover the organic phase. The process can minimize the loss of neutral oil and retains bioactive compounds.

Liquid-liquid extraction is used particularly for the winning of compounds that are not very volatile, which occur in small amounts in solution along with numerous other substances.
Liquid-liquid extraction

Supercritical fluid extraction

Supercritical fluid extraction uses a supercritical fluid, such as CO2, with or without an added organic modifier, such as CH3CN or CH3OH or their mixtures, to extract the required compound from the matrix.

Supercritical fluid extraction has the great advantage of low energy cost, high yield, superior quality (since a lower extraction temperature range is used), absence of potentially explosive or toxic solvents, and absence of toxic by-products.

A basis for many supercritical fluid process is that the solubility of a dissolved compound is a strong function of pressure and temperature near the solvent’s critical point.

The large change in solubility simply reflects the large change in density, or solubility, which characterizes the solvent strength.

Supercritical fluid extraction has been used for a long time in the food industry.

It has been applied to delipidation of protein, deoiling of lecithin, isolation of important oils, fractionation of butterfat, decaffeination of coffee, oil extraction from oil seeds, removal of bitter aroma compounds from hops, extraction of spices, and removal of cholesterol from different foods.
Supercritical fluid extraction

Solvent extraction of lipids

Lipids are removed from lipid-containing materials by two methods: mechanical crushing and solvent extraction. Solvent extraction systems rely on solubility differences between lipids and other food components in particular system.

These solubility differences primarily relate to issues of charge or polarity and the nature of the association between lipids and the other components within the material to be extracted.

Neutral or non-polar lipids such as hydrocarbons, sterol esters, acylglycerols and carotenoids can be bound through non-covalent interactions such as van der Waals forces and hydrophobic associations between hydrocarbon chains of lipids and hydrophobic protein domains within foods.

Soxhlet apparatus

The extraction of polar lipids requires more polar solvents such as ethanol or methanol to disrupt these molecular interactions.

Depending on its efficiency the extraction procedure should be repeated to ensure total recovery of lipids. Generally, extractions are performed in triplicate.

Solvent extraction becomes more efficient when sample is heated and extraction is continues. In a Soxhlet apparatus, dried and homogenized sample are weighed in thimbles that are subjected to steady extraction with heated solvent for several hours.
Solvent extraction of lipids

Animal fats processing

For centuries animal fat was the principle edible source. Handing and processing animal fats have evolved from the primitive to state-of-the-art processing equipment and technology. Processing of animal fat for edible use may ranges from simple to complex.

If fat is selectively removed from the animal carcass and carefully rendered, the result product can be simply filtered to remove particulate.

For more complex products with more rigorous quality specifications, the complete processing train of caustic refining, bleaching, hydrogenation, blending and deodorization is used.

Animal fats recovered from fatty tissues by cooking processes known as rendering. The two predominant rendering processes are wet and dry rendering.

In wet rendering, the fatty tissue is heated under steam pressure, thus rupturing the cells and liberating the fat.  The lard produced by this method of rendering is known as ‘prime steam lard’. In addition to lard, tallow and whale oil also usually steam rendered. The wet process is preferred for edible animal fats.

In dry rendering, the fatty tissue is heated in jacketed drums with agitation until the fats is released. Presently, centrifuges are used to separates the fat from water and protein. The dry rendering process is preferred for inedible products.
Animal fats processing