Enzymatic modification of lecithin for improved antioxidant activity in combination with tocopherol in emulsions and bulk oil

Industry attempts to meet consumers' clean label demands by removing synthetic antioxidants (e.g. EDTA) frequently result in deleterious effects on oil quality, causing the formation of toxic oxidation derivatives as well as off-flavors and aromas. Thus, there is an urgent need for novel and natural antioxidant systems. For example, after becoming oxidized, α-tocopherol can be recharged to its active form by phosphatidylethanolamine (PE) for increased efficacy. Unfortunately, plant-based lecithin is mostly phosphatidylcholine (PC), which lacks the amine group necessary to recharge tocopherol. Purified phospholipids are typically too expensive for food products, however enzymatic conversion of PC to PE is more cost effective.The aims of the present study are 1) to determine the optimal reaction conditions for converting high PC lecithin into modified high PE lecithin (MHPEL) and 2) to validate the MHPEL's synergism with tocopherol in delaying lipid oxidation in model emulsion systems at pH 7, and 4, and in bulk oil. High PC lecithin was incubated with phospholipase D from Streptomyces chromofuscus and ethanolamine at varied pH, temperature, and time and then analyzed for compositional changes by HPLC. To assess shelf life, aliquots of 1% o/w emulsions buffered to pH 7 and 4 as well as bulk oil were prepared and stored at 32 and 55°C, respectively. Treatment groups included control, MHPEL, purified PE standard, tocopherol, tocopherol + MHPEL, and tocopherol + purified PE standard. Lipid hydroperoxide formation was measured spectrophotometrically, and hexanal formation was measured using GC headspace analysis. Maximum conversion occurred at pH 9 and 37°C, reaching >73% PE after 4 hours. The combination of MHPEL and tocopherol increased shelf-life by 75% compared to tocopherol alone in o/w emulsions at pH 7, 50% in o/w emulsions at pH 4, and 100% in bulk oil. This approach represents an exciting and clean-label antioxidant system with commercialization potential.