Antioxidant and prooxidant activity behavior of phospholipids in stripped soybean oil-in-water emulsions

Phospholipids have been reported to inhibit lipid oxidation in bulk oils, but very little is known about their influence on oxidation in oil-in-water emulsions. In the present study, the impact of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) on lipid oxidation was studied in 1% stripped soybean oil-in-water (O/W) emulsions as a function of DOPC concentration and pH (3 and 7). At pH 7.0, DOPC inhibited lipid oxidation in O/W emulsions, while DOPC was prooxidative at pH 3.0. DOPC did not affect emulsion droplet charge or size at either pH 3.0 or 7.0 The antioxidant activity at pH 7.0 was observed in a series of phospholipids (PL) that varied in fatty acid unsaturation level and chain length as well as type of phosphate head group. Overall, phosphatidylcholine with either oleic or palmitic acid were the most effective at inhibiting lipid hydroperoxide and hexanal formation of all of the PLs tested. Antioxidant mechanism of PLs could not be ascribed to their ability to decompose lipid hydroperoxides. It might be possible that, at pH 7.0, the PLs antioxidant activity is related to their ability to form structures within the lipid phase of the emulsions droplets or to chelate metals.