1. Technical Overview

Carbon dioxide supercritical fluid extraction (CO2 SCFE) is more effective in the segregation of non-polar, volatile, and low molecular weight phytochemicals because supercritical CO2 is naturally non polar [1]. A selective process, supercritical fluid extraction (SCFE) separates, for example, phenolic phytochemicals from Euterpe oleracea pulp at a certain pressure while removing anthocyanin from the same pulp at another pressure [1].

Figure 1. Use of nutritional supplements is growing
Image credits: Steve Buissinne at Pixabay

Plants naturally produce phytochemicals. Research has proved their utility in preventing and fighting cancer, inflammation, mutation, oxidation [2], and ageing [3]. As many as 4,000 phytochemicals are identified and 150 of these have been investigated in detail [4].

CO2 SCFE can even extract some polar phytochemicals, but not those located inside the cell wall. Addition of small quantities of solvent modifiers or organic co-solvents such as methanol and ethanol can overcome this limitation [1].

SCFE delivers better extraction yields when combined with ultrasound extraction, microwave radiation, and enzyme pre-treatment. For example, exposing Perilla frutescens leaves to ultrasound for 125 seconds substantially improves the yields of luteolin and apigenin [1].

2. Global Phytochemical Market

Phytochemicals market is galloping thanks to their ability to fight and ward off various diseases and supply essential nutrients without producing side effects. The market is expected to reach $9 billion by 2029 [5].

Epicatechin, a phytochemical, upgrades the nutritional value of bread. Carotenoid is another phytochemical that imparts natural color to food. Broadly, phytochemical types are [6]:

  • Carotenoids
  • Phytosterols
  • Flavonoids

Riding the organic boom, the phytochemical market is rapidly gaining ground. Industry stimulants include:

  • Capacity of pytochemicals to naturally fight disorders such as diabetes, cancer, obesity, hypertension and others [3].
  • Improved awareness on the health benefits of organic food, and natural ingredients in foods and beverages [5].
  • Declining preference for synthetic chemical based medicines, foods, beverages, and other products [5].
  • Surging meat and dairy consumption [3].

Established applications of phytochemicals include [5]:

  • Functional Food
  • Pharmaceutical
  • Foods-beverages
  • Neutraceuticals
  • Cosmetics
  • Animal Feed

3. Supercritical Fluid Extraction (SCFE) & Carbon dioxide (CO2) SCFE

3.1. Why SCFE Use is Rising?

Regulations on toxicity, quality, safety, and residues in consumer products are getting stricter as consumers demand products with more natural ingredients in food-beverage, pharmaceutical, neutraceutical, and personal care products. SCFE is safer, more eco-friendly, and leaves behind zero or less toxic residues in the final product.

Alternative methods have drawbacks:

  • Solvent Extraction: uses toxic organic solvents whose residue cannot be completely separated from the extracted ingredient [7]. Some solvents deplete the ozone layer and create environmental issues [8].
  • Hydrodistillation: employs heat which can thermally degrade the ingredient [9].

3.2. What are Supercritical Fluids & How do they Assist with Extraction?

A fluid at above its critical pressure and temperature is a supercritical fluid. The phase boundary between its liquid and vapour phase disappears and its properties can be customized by changing the pressure and temperature.

Roughly, supercritical fluids with higher density possess greater solvent power. And because altering pressure and temperature substantially varies their density, supercritical fluids make exceptional solvents.

Figure 2. Triple Point Parameters

Supercritical fluids are excellent solvents because of their [10]:

  • Higher, Liquid-like Density: boosts solvent power.
  • Low, Gas-like Viscosity: improves mass transfer and diffusion inside porous solids.
  • Low, Gas-like Surface Tension: enables greater seepage inside porous solids.

3.3. Why Supercritical Carbon dioxide (CO2) Makes an Excellent SCFE Solvent?

Carbon dioxide and water are the most popularly utilized supercritical fluids [11]. Supercritical (CO2) is an ideal solvent for SCFE because it [10]:

  • Has a critical temperature of 31.10C, which is around the ambient temperature. Relatively low temperatures for CO2 SCFE avoid thermal degradation.
  • Has a more manageable critical pressure of 73.9 bar.
  • Is non-flammable and non-toxic.
  • Has a customizable density to upgrade its solvent power.
  • Is available in ample quantities and in pure form.
  • Has a comparatively low cost.

Although CO2 is a greenhouse gas (GHG), the SCFE process using CO2 becomes eco-friendly if the gas is captured from the atmosphere, reused, and recycled.


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References

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6152233/
  2. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phytochemical
  3. https://www.theinsightpartners.com/reports/phytochemicals-and-plant-extracts-market
  4. https://www.futuremarketinsights.com/reports/phytochemical-api-market
  5. https://www.globenewswire.com/news-release/2019/08/12/1900582/0/en/Phytochemicals-Market-is-Expected-to-Reach-US-9-0-Bn-by-2029-PMR.html
  6. https://www.marketsandmarkets.com/Market-Reports/phytochemical-plant-extract-market-268182066.html
  7. https://www.sciencedirect.com/topics/immunology-and-microbiology/solvent-extraction
  8. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/organic-solvent
  9. http://www.florajournal.com/archives/2019/vol7issue1/PartA/7-3-34-739.pdf
  10. https://www.chemengonline.com/supercritical-co2-a-green-solvent/?printmode=1
  11. https://en.wikipedia.org/wiki/Supercritical_fluid