How to extract beta-carotene from microalgae?

Extracting β-carotene from microalgae is an important development direction for natural pigments and functional ingredients.

Principle

Utilizes the high permeability and solubility of CO₂ under supercritical conditions (high pressure and specific temperature) to selectively extract β-carotene.

Process

• Pretreatment: Dry and pulverize microalgae (such as Dunaliella salina) to disrupt the cell walls.
• Extraction Conditions:

Pressure: 30–40 MPa (30 MPa for Dunaliella salina, 40 MPa for other microalgae)

Temperature: 45–60°C (45°C for Dunaliella salina; 60°C for Scenedesmus almeriensis)

CO₂ Flow Rate: 10 L/h (Dunaliella salina) or 1 g/min (for other algae)

Time: 5–6 hours.

• Optimization: Add an entrainer (such as ethanol) to increase the solubility of β-carotene in CO₂.

Advantages

• Extraction yield reaches up to 95.09% (salina), and the cis-isomer ratio reaches 82%, indicating higher activity.
• No solvent residue, high product purity, and compliance with food/pharmaceutical standards.

Principle

A hydrophilic solvent (alcohol) is used to form a two-phase system with salt/sugar, enriching β-carotene in the organic phase.

Common Systems and Processes

• Ethanol-Acetone/Ammonium Sulfate System (for Spirulina):

15% (ethanol + acetone) + 24% ammonium sulfate;

6% solid-liquid ratio, pH 8.0, extraction at 30°C, extraction yield 94.55%.

• Ethanol-n-Butanol System:

8.2% ethanol + 36% n-butanol, solid-liquid ratio 1:20, ultrasonication for 3 minutes, yield 3.13 mg/g.

• Tert-Butanol-Maltose System:

Ultrasound-assisted extraction (90 W, 5 min), yield 3.19 mg/g.
 

Principle

Ultrasonic cavitation destroys the microalgae cell wall, accelerating solvent penetration.

Key Operational Tips

• Solvent Combinations:

Petroleum ether-acetone, methanol-acetone, or tetrahydrofuran;

n-Butanol-ethanol mixture (reduces the use of toxic solvents).

• Parameter Optimization:

Ultrasound Power: 90–325 W;

Time: 3–5 minutes (excessive use may cause isomerization).

Principle

Cellulase and pectinase hydrolyze the microalgae cell wall to release intracellular components.

Procedure

• Microalgae slurry is pretreated with an enzyme solution (pH 4.5–5.0) at 40–50°C;
• Secondary extraction is performed with an organic solvent (e.g., n-hexane).

Limitations

Enzymes are easily inactivated in organic solvents, so the timing of solvent addition must be carefully controlled.

Steps

• Microalgae powder is mixed with 95% ethanol and acetone (e.g., a 1:2 ratio);
• Microwave treatment is performed (power 300–600 W) for less than 10 minutes.

Risks

Overheating may cause thermal degradation or isomerization of β-carotene.

• Stability Control: β-carotene is easily degraded by light, heat, and oxygen. The entire process must be performed in the dark and under nitrogen.
• Comprehensive Utilization of Algal Residue: For example, the residue after β-carotene extraction from Dunaliella contains polysaccharides (10%), which can be further isolated for anti-tumor active components.
• Solvent residue: For food/pharmaceutical use, it must comply with GB 2760 or FDA standards, and supercritical or low-toxic two-phase aqueous systems are preferred.