Effects of roselle extract on the oxidative stability of hempseed oil

Hempseed oil is exceptionally rich in valuable unsaturated fatty acids if adequate oxidative protection is ensured. The aim of this study was to investigate its stability at 60 degrees C in the presence of roselle (Hibiscus sabdanffa) extract rich in anthocyanins (7206.6 mg.kg(-1) dry weight) and characterized by high antioxidant and antiradical activities. Thermal degradation of the oil during storage was evaluated on the basis of the fatty acid profile using analysis by gas chromatography-mass spectrometry and kinetic studies based on peroxide value and differential scanning calorimetry measurements. The evolution of the unsaturated fatty acids showed protective properties of the natural extract against lipid oxidation. Accumulation of peroxides in oil was reduced by 56 % in the presence of roselle extract compared to untreated oil, which was confirmed by kinetic analysis of the induction period. The thermal degradation kinetics using the Ozawa-Flynn-Wall method indicated that 0.2% (w/w) addition of roselle extract to hempseed oil improved its stability due to higher activation energy compared to other samples. The antioxidant effect of Hibiscus extract was also validated by Fourier-transform infrared spectroscopy. Our findings indicate that H. sabdanffa can be a safe and effective natural alternative to synthetic antioxidants applied to hempseed oil.