Supercritical CO₂ extract

A supercritical CO₂ extract is a dense botanical extract obtained by washing plant material with carbon dioxide (CO₂) under pressure. When the pressure drops, CO₂ evaporates as a gas. Only the substances extracted from the plant remain. This mild process also captures heavy components that steam cannot carry and leaves no solvent residue in the extract. Food, cosmetic and supplement manufacturers use it for scent, taste, color and active substances. The same plant can also yield essential oils, absolutes or oleoresins. The difference lies in the extraction method.

What is a supercritical CO₂ extract?

Carbon dioxide becomes a solvent under pressure. A solvent is a liquid that extracts substances from plant material. In supercritical CO₂ extraction, pressurized CO₂ mainly dissolves small lipophilic molecules and dissolves few hydrophilic molecules [1]. Therefore, aroma compounds, plant lipids, oil-soluble pigments and antioxidants pass into the CO₂ extract. Rosemary extract obtained with CO₂ was found rich in antioxidant carnosic acid [2]. Red pepper CO₂ extract contains its coloring carotenoids [3]. Amaranth seed oil extracted with CO₂ contains squalene [4].

Pressure settings determine the product. Low pressure extracts light and volatile aroma components. High pressure also captures heavier aroma components and waxes [5]. The same plant can therefore yield two products: a light, fluid volatile fraction similar to an essential oil, and a dark, dense total extract. Differences: volatile fraction and total extract.

What is it used for?

A CO₂ extract carries the scent, taste, color and oil-soluble components of the plant in concentrated form. Manufacturers add small amounts to their formulations.

Food: taste, color, natural additive. Ginger oleoresin obtained with CO₂ was proposed as a natural food additive due to its high antioxidant content [6]. Carotenoids in red pepper CO₂ extract give food a red color [7].

Cosmetics: skin-compatible lipids. Amaranth seed oil obtained with CO₂ carries squalene [4]. Squalene occurs naturally in skin surface lipids. It is used as an emollient in cosmetics and creams [8].

Supplements: concentrated active substances. A glabridin-rich CO₂ extract of licorice root was administered to mice on a high-fat diet for eight weeks. The extract reduced body weight gain in a dose-dependent manner [9].

Why choose a supercritical CO₂ extract?

Components not obtained by other methods. A CO₂ extract also carries heavy components that steam cannot transport: carnosic acid, carotenoids and pungent ginger compounds [2], [3], [6]. Because the process operates at mild temperatures, heat-sensitive components are obtained without degradation [1].

Short answers on documentation. Food and cosmetic brands require composition and residue declarations from suppliers. When pressure drops, CO₂ separates as a gas and does not remain in the extract [6]. Residues depend on the extraction solvent. Organic solvents are not used in CO₂ extraction. In some extractions, a small amount of ethanol is added to CO₂ as a co-solvent and is subsequently evaporated. Ethanol is on the European Union list of extraction solvents requiring no numerical limit for food use [10]. In pharmaceutical guidelines, it is classified as a solvent with low toxic potential, with a limit of 5,000 ppm [11]. If ethanol was used, the technical data sheet includes an ethanol residue line.

One extract, multiple functions. A single CO₂ extract performs several functions in a formulation. Carotenoids in red pepper extract provide both red color and antioxidant properties to food [7]. Ginger oleoresin provides the scent and pungency of ginger and was proposed as a natural additive due to its antioxidant content [6].

How does it differ from an essential oil?

Essential oil is the steam-volatile fraction. Essential oil is mostly obtained by steam distillation. Steam is passed through the plant material. Scented components carried by steam condense upon cooling and collect as oil on top of water. Heavy components that cannot travel with steam remain in the plant. Citrus peel oil, by contrast, is mostly cold-pressed: the oil glands in the peel are pressed mechanically. The main component of citrus peel oil is limonene.

CO₂ extracts contain heavy components in addition to essential oil compounds. Therefore, their color and consistency are often different. In Diamante citron peel, CO₂ extracts were found richer in heavier aroma compounds and waxes compared to distilled oil [5].

What is an absolute?

An absolute carries the scent of delicate flowers. Delicate flowers like rose yield very little oil with steam distillation [12]. These flowers are first washed with a solvent. The resulting waxy product is called a concrete. The concrete is mixed with cold alcohol, waxes precipitate, and the alcohol-soluble scented portion is separated. When alcohol is removed, the absolute remains [13].

The composition of an absolute differs from an essential oil. In rose absolute, the main component was phenylethyl alcohol, which gives rose its honey-like, sweet note. It measured 78%. In distilled rose oil, the main components were two rose-scented compounds, citronellol and geraniol [14].

What is an oleoresin?

An oleoresin carries the full profile of a spice. An oleoresin is a dense extract containing the scent, taste and pungency of a spice together. It is considered a concentrated form of the spice [15]. Ginger oleoresin is a dark brown, viscous liquid. Besides essential oil, it contains gingerols that provide pungency [6].

Oleoresins are obtained with solvents or CO₂. Traditional oleoresins are extracted with an organic solvent, which is then removed [6]. A total extract obtained with CO₂ is also called an oleoresin [6], [3]. Red pepper oleoresin was extracted with CO₂, and yields of oleoresin and pigments increased with higher pressure [3].

What does the name tell you?

The method shows in the product name. Labels use different words for the same kind of product. The name of a CO₂ extract usually contains "SFE" (supercritical fluid extraction), "supercritical CO₂" or "scCO₂". The designation also appears on the first line of the technical data sheet (TDS).