In-situ reverse micelle-assisted extraction of polar antioxidants for improving oxidative stability of nonpolar flaxseed oil based on polar paradox theory

Flaxseeds are rich in α-linolenic acid, which is highly unsaturated and easily oxidized. Since adding antioxidants is the most common and effective method, natural antioxidants are becoming more popular with the increasing concern of food safety. Based on the special antioxidant effect of polar antioxidants in the oil system described in the polar paradox theory, this study used flaxseed oil as the solvent to directly extract natural antioxidants so that a new type of antioxidant oil system with associative colloids (i.e., reverse micelles) inside could be constructed in situ, which was further optimized with ultrasound to improve extraction efficiency and antioxidant effectiveness. The results showed that this new system had the highest antioxidant content under the optimal conditions of 135 W, 11 min and 31°C. The storage stability was much better than the traditional TBHQ-added flaxseed oil system. In addition, the existence of nanoscale spherical reverse micelle structure (diameter about 2 nm) was confirmed in the new antioxidant flaxseed oil system through small-angle X-ray scattering analysis, which further explains the extraction mechanism. The antioxidant mechanism of the new system was preliminarily explored by tracking the migration of free radicals using electron paramagnetic resonance, and the influence of emulsifier type, moisture content, oxidation temperature and time on the critical micelle concentration was determined in such flaxseed oil system, which lays the foundation for precise regulation of the association colloids formation in highly unsaturated oils and effective improvement of lipid oxidative stability.