Oxidative stability of flaxseed oil: Effect of hydrophilic, hydrophobic and intermediate polarity antioxidants

Oxidative deterioration is a major issue limiting the utilization of flaxseed oil (FSO). Present study explored the effects of hydrophilic (tannic acid), hydrophobic (alpha-tocopherol), and intermediate polarity (ascorbyl palmitate) natural antioxidants, which displayed highest DPPH radical scavenging and iron chelating abilities among several others, on the oxidative stability of FSO. A synthetic antioxidant (TBHQ) was also used as a control. FSO oxidation was examined by peroxide and p-anisidine values during 30-day storage at 25, 40 and 60 degrees C, and by accelerated oxidation using a rancimat at 110 degrees C. On mass concentration basis, all natural antioxidants were less effective than TBHQ. Irrespective of the polarity, all natural antioxidants, except alpha tocopherol, delayed primary and secondary oxidation, and increased the oxidative stability index. The alpha-tocopherol displayed pro-oxidant effect at all concentrations. Rather than polarity, antioxidant capacities, and their ability to replace minor components from the oil-water interface were crucial for the protection of FSO.