Supercritical CO2 extraction and fractionation of turmeric polyphenols: Antioxidant capacity and inhibition of lipid oxidation in sunflower oil

Turmeric (Curcuma longa) is a rich source of antioxidants, including polyphenols and curcuminoids. This study investigates the antioxidant capacity and oxidative stability of a polyphenol-rich fraction obtained via supercritical fluid extraction (SFE) with supercritical CO₂. Optimized extraction conditions (300 bar, 40 °C, CO₂ flow rate: 1 L/h, 20 % w/w ethanol) yielded 11.4 ± 0.3 % (w/w) crude extract. Fractionation separated a hydrophilic Fraction B, rich in polyphenol and weak in curcuminoids, and a Fraction C, weak in polyphenol and rich in curcuminoids. Fraction B showed the highest total phenolic content (476 ± 6 mmol/L GAE/g dry matter) and superior antioxidant activity in DPPH, ABTS, and ORAC assays. HPLC-MS identified curcumin, demethoxycurcumin, bis-demethoxycurcumin, phenolics, and phenolic terpenoid hybrids, highlighting their potential contributions to antioxidant efficiency and the synergistic radical-scavenging interactions that influence oxidative stability. Turmeric fractions were added to the stripped sunflower oil. Isothermal calorimetry confirmed that an oil enriched with Fraction B prolonged the induction period of lipid oxidation (11.4 ± 0.3 h) at 30 °C in the presence of AIBN (20 mmol/L) as a free radical initiator, outperforming Fraction C. These findings highlight the potential application of turmeric extracts in functional foods and nutraceuticals to increase their stability against oxidation.