Methodological Optimization of Supercritical Fluid Extraction of Valuable Bioactive Compounds from the Acidophilic Microalga Coccomyxa onubensis

Can a tiny alga from a toxic river hold the key to greener extraction? For the first time, scientists have used supercritical fluid extraction to unlock valuable compounds from Coccomyxa onubensis.

In the heart of Spain's mining belt, the Tinto River's acidic waters harbor a microscopic treasure: the alga Coccomyxa onubensis. This eukaryote thrives where few others can, packing a punch of bioactive compounds with potential for nutraceuticals and functional foods. But getting those compounds out efficiently has been a challenge—until now.

Researchers turned to supercritical fluid extraction (SFE), a green, energy-saving method already used across industries. Using a Box–Behnken design, they tested how temperature, pressure, and ethanol co-solvent percentages affected extraction. The results were striking: co-solvent and temperature mattered most, with pressure playing a lesser role.

At 70°C, 40 MPa, and 50% ethanol, the alga yielded a maximum lutein recovery of 66.98%. Meanwhile, the richest phenolic extracts—36.08 mg gallic acid equivalents per gram—and peak antioxidant activity (2.237 mmol Trolox equivalents per gram) emerged under similar conditions but different temperatures (30°C and 70°C, respectively).

This isn't just lab trivia. The extracts could find their way into food, cosmetics, and health products. More importantly, SFE offers a sustainable way to valorize extreme-environment microbes that green methods have barely touched. The river's secret is out.

Key Points

• First SFE study on acidophilic alga Coccomyxa onubensis
• Max lutein recovery 66.98% at 70°C, 40 MPa, 50% ethanol
• Co-solvent and temperature are the most significant factors