The Impact of Hypericum perforatum L. as an Organic Free-Radical Scavenger in Biodiesel-Diesel Blends

The extraction of Hypericum perforatum L. (HP) was performed using the Soxhlet extraction method to evaluate its potential as an organic free-radical scavenger in biodiesel-diesel blends. Experimental blends—B100, B20D80, B20D80BHT, and B20D80HP—were prepared, incorporating Hypericum perforatum L. extract at a concentration of 3000 ppm, and compared with butylhydroxytoluene (BHT). The antioxidant properties were assessed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), high-performance liquid chromatography (HPLC), and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. DSC analysis ranked the antioxidant efficiency as D100 < B20D80 < B20D80BHT < B20D80HP, demonstrating the superior stabilization effect of Hypericum perforatum L. extract. TGA and FT-IR results confirmed enhanced thermal stability, while HPLC identified key phenolic compounds such as rutin, ellagic acid, and kaempferol, which contribute to antioxidant activity. DPPH assays further confirmed the extract’s superior free-radical scavenging efficiency compared to BHT. These findings highlight Hypericum perforatum L. as a promising natural antioxidant for improving biodiesel oxidative stability.