Application of Silibinin Oleate as a Nutraceutical Antioxidant for Improving the Quality of Sunflower Oil

Sunflower oil is particularly prone to thermo-oxidative degradation due to its high content of polyunsaturated fatty acids, especially under high-temperature conditions. This study investigated the oxidative stability of sunflower oil heated at 180 °C for 4 and 8 h, focusing on the protective effect of silibinin oleate (SIL-O), a lipophilic polyphenolic derivative, compared to the synthetic antioxidant butylated hydroxytoluene (BHT). Oxidative changes were evaluated through peroxide value (PV), p-anisidine value (p-AV), and total oxidation value (TOTOX), while structural alterations were monitored using FTIR spectroscopy. Additionally, fatty acid composition was analyzed by GC-MS to assess compositional changes associated with oxidation. Thermal treatment led to increases in PV, p-AV, and TOTOX, indicating progressive oxidation, alongside a decrease in unsaturated fatty acids. FTIR analysis revealed characteristic changes, including a reduction in the unsaturation band (~3008 cm−1), modifications in the ester carbonyl region (~1743 cm−1), and the emergence of bands associated with cis–trans isomerization (~968–970 cm−1). Strong correlations were observed between fatty acid degradation, FTIR indices, and oxidation parameters. Compared to the control, SIL-O inhibited oxidation in a dose-dependent manner. At 300 ppm, it outperformed BHT, demonstrating its potential as a natural antioxidant for enhancing the stability of sunflower oil during high-temperature processing.