Supercritical CO₂ Extraction of the Oat Lipids for Functional Food Ingredients

Introduction: Oats (Avena sativa L.) contain 5–9% lipids with a unique fatty acid profile rich in oleic, linoleic, and palmitic acids. While conventional solvent extraction raises environmental concerns, alkaline methods cause undesirable phenolic oxidation. This study investigates supercritical CO₂ (SC-CO₂) extraction as a green biorefining strategy to recover lipid-enriched fractions from oat matrices, supporting a sustainable valorization model where defatted residues can be further processed for protein and fiber recovery.

Methods: Proximate analysis was first conducted on various oat fractions: fine powder (70 mesh), husk with powder (18 mesh), and husk (7 mesh). Because the fine powder fraction exhibited the highest lipid (5.77%) and protein (11.19%) content, it was selected for SC-CO₂ extraction. Extraction was performed at varying temperatures (40–50 °C) and pressures (250–450 bar). The extracted oils were analyzed for fatty acid profiles, triacylglycerols, total carotenoids, tocopherols, phytosterols, and oxygen radical absorbance capacity (ORAC) antioxidant activity.

Results: Proximate analysis confirmed that ash content was highest in the husk fraction (3.14%). For the extraction phase, pressure and particle size emerged as the most significant factors influencing oil yield. SC-CO₂ extraction yielded the highest oil content from the fine powder at the maximum pressure of 450 bar, which was lower than the yield obtained via traditional Soxhlet solvent extraction with hexane. However, co-extracted polyphenols significantly contributed to the extracted oil's antioxidant activity.

Conclusions: Although SC-CO₂ extraction resulted in a lower lipid yield compared to traditional methods, these results confirm that this green technology successfully produces a solvent-free, bioactive oat lipid ingredient. Furthermore, this approach preserves the defatted oat residue, allowing for subsequent downstream isolation of valuable beta-glucans and proteins within a circular biorefinery concept.