Supercritical carbon dioxide extraction of Gac oil

Supercritical CO₂ Extraction System – TST Manufacturer, Taiwan

Gac Fruit: A Valuable Source of Nutrients

Gac (Momordica cochinchinensis) is a highly valuable fruit containing numerous bioactive compounds. However, conventional extraction methods typically recover only about 87% of these micronutrients. Recently, new extraction technologies developed both globally and in Vietnam have achieved up to 91.5% nutrient recovery, with potential for nearly 100% solvent-free purification.

Gac fruit is exceptionally rich in essential nutrients such as α-carotene, β-carotene, and lycopene, which provide significant health benefits. Studies have shown that β-carotene content in gac aril is 9–15 times higher than in carrots, and lycopene levels are 68 times higher than in tomatoes and 54 times higher than in watermelon. β-carotene is a powerful antioxidant that helps prevent aging and oxidative stress-related disorders of the lungs, heart, blood vessels, and nervous system.

Gac is a perennial vine belonging to the Cucurbitaceae family, commonly grown across Southeast Asia, including Vietnam. Despite its wide distribution, gac cultivation in Vietnam remains limited, mainly as scattered plants along fences or small garden plots. Traditionally, gac fruit has been used as a natural food colorant and flavoring in festive dishes such as xôi gấc (sticky rice with gac), and in local confectionery.

In recent years, gac has gained industrial significance due to the extraction of gac oil, which contains high levels of vitamin A and E, thereby greatly increasing its economic value. Each vine can produce 15–20 fruits per season, and with proper care, yields can reach several dozen kilograms per plant. The plant is resilient, low-maintenance, and long-lived (15–20 years), making it a potential poverty-reducing crop with strong commercial potential.

Market prices for gac vary from 15,000 to 65,000 VND/kg, and can rise to 80,000–85,000 VND/kg during peak seasons. After preliminary processing, gac can reach 150,000–200,000 VND/kg, and gac oil extracted via advanced methods can sell for over 1,000,000 VND/kg.

Supercritical CO₂ Extraction Technology

The traditional mechanical pressing or solvent extraction methods used for plant-derived compounds have limitations, especially the low yield of bioactive components in the extracted product.

In contrast, supercritical CO₂ (SC-CO₂) extraction technology has been successfully applied worldwide in the production of essential oils, natural flavors, and lipid fractions rich in DHA and EPA, serving the food, pharmaceutical, and cosmetic industries.

Although the concept of using CO₂ as a solvent dates back more than 130 years, its modern application has evolved through decades of research:

• 1861 – Gore discovered that liquid CO₂ could dissolve camphor and naphthalene effectively, producing vivid colors but showing limited solubility for fats.
• 1875–1876 – Andrews studied the supercritical state of CO₂, describing it as an intermediate phase between liquid and gas.
• 1920–1960 – Numerous studies were conducted on supercritical solvents, with CO₂ emerging as the preferred choice due to its unique physicochemical properties.
• 1980s onward – Supercritical CO₂ technology gained widespread attention and industrial-scale applications.

Principle of the Supercritical CO₂ Process

Under normal conditions, substances exist in solid, liquid, or gaseous states depending on temperature and pressure. When a gas is compressed to a sufficiently high pressure, it condenses into a liquid. However, beyond a certain point — known as the critical point — if the temperature continues to increase, the substance enters a unique state called the supercritical phase.

At this supercritical condition (for CO₂: 31°C and 73.8 bar), CO₂ exhibits properties of both a liquid and a gas — it behaves as a dense solvent capable of dissolving a wide range of organic compounds.

When CO₂ is heated and pressurized beyond these critical parameters, it transforms into a supercritical fluid capable of dissolving compounds in solid, liquid, or gas matrices. After extraction, reducing the pressure below the critical point allows CO₂ to revert to its gaseous state, leaving behind a pure, solvent-free product.

Because CO₂ is non-toxic, non-flammable, and chemically inert, the resulting extract is 100% clean, making it ideal for applications requiring high purity and biological activity.

Advantages of Supercritical CO₂ Extraction

• High product purity and safety (no solvent residues).
• Excellent preservation of bioactive compounds due to mild operating temperatures.
• Adjustable selectivity via changes in pressure and temperature, enabling fractionation of compounds at different concentrations.
• Environmentally friendly and sustainable process — CO₂ can be fully recovered and reused.
• Enhanced commercial value of extracts with superior stability and bioactivity.

Global Development of Supercritical CO₂ Technology

Supercritical CO₂ extraction has been widely adopted across multiple countries and industries:

• India: Extraction of active compounds from spices and herbs.
• New Zealand & Poland: Extraction of hop components and herbal ingredients.
• Spain: Treatment of cork stoppers to remove odors without affecting wine quality.
• Germany & Italy: Decaffeination of coffee and tea.
• Taiwan: Removal of pesticide residues from rice to produce “clean rice.”
• South Korea: Production of sesame oil using supercritical CO₂.

According to Wipsglobal patent data, since 1980, nearly 300 patents have been registered worldwide for supercritical CO₂ extraction technologies. The first patent (US4308200), filed in the United States in 1980, described the use of supercritical CO₂ for extracting pine resin and oil.

Currently, China accounts for over 50% of all patents related to this technology, reflecting its strong research and industrial adoption.

Applications covered by these patents include:

• Extraction of vegetable oils and fats – 16.84%
• Extraction of essential oils – 4.81%
• Extraction of herbal compounds – 14.78%
• Application in food industry – 11%
• Application in cosmetic industry – 2.06%
• Technical and methodological innovations – 15.81%

Application of Supercritical CO₂ Extraction in Vietnam

In Vietnam, supercritical CO₂ technology has been used primarily for extracting cajeput essential oil, but its application for gac oil extraction remains limited. Conventional pressing or solvent-based extraction methods yield only 81–87% of bioactive components, resulting in lower-quality oil unsuitable for high-end food, pharmaceutical, or cosmetic formulations.

Recent research by Dr. Phan Tai Huan, Faculty of Food Technology, University of Agriculture and Forestry, Ho Chi Minh City, demonstrated that supercritical CO₂ extraction can achieve a 91.5% extraction efficiency for gac oil.

Compared to traditional methods, the results are striking:

• Vitamin E content: 3,000–6,000 ppm (vs. ~400 ppm)
• β-carotene: 20,000 ppm (vs. ~3,500 ppm)
• Lycopene: 4,000 ppm (vs. ~3,800 ppm)

The oil obtained through SC-CO₂ extraction is purer, richer in nutrients, and completely free of toxic organic solvents, making it ideal for fractional extraction and high-value applications.

Outlook

The application of advanced supercritical CO₂ extraction technology opens new directions for agricultural product diversification, enhances added value of raw materials, and promotes economic development in agricultural regions.

Source:
Hoang Mi – STINFO Journal, Issue 11/2014