Changes of molecular mobility of ascorbyl palmitate and α-tocopherol by phospholipid and their effects on antioxidant properties in bulk oil

Abstract: Phospholipids are amphiphilic compounds and have synergistic or antagonistic dual effects against lipid oxidation. Proton mobility analyzed by nuclear magnetic resonance (NMR) relaxation technique may provide a useful information on the reactivity of antioxidants in the presence of minor compounds.

The objectives of this study were to determine molecular mobility of protons of ascorbyl palmitate and α-tocopherol in the presence of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) using NMR relaxation technique and to evaluate synergistic effects of DOPC on ascorbyl palmitate in diverse in vitro systems.
Effects of DOPC on the antixodiant activities of ascorbyl palmitate or α-tocopherol were evaluated using in vitro assays and corn oil matrix at 60 °C for 18 days The NMR experiments were conducted with VNS-600 NMR spectrometer (Varian Inc., Palo Alto, CA, USA) operating at 600 MHz.
Synergistic effects of DOPC on the antioxidative capacities of ascorbyl palmitate were evaluated in DPPH radical scavenging assay and bulk oil matrix. NMR relaxation technique can provide information on the mobility of protons. Molecular mobility of two protons in hydroxyl group of ascorbyl palmitate decreased by 85 and 78% in the presence of DOPC compared to those without DOPC. However, proton mobility of α-tocopherol increased by 41% when DOPC was present. DOPC significantly enhanced the DPPH reactivity in medium chain triacylglycerol, while this effect was not observed in α-tocopherol. Mixture of ascorbyl palmitate with DOPC showed synergistic antioxidant properties in corn oil at 60 °C. DOPC may make protons of ascorbyl palmitate in more rigid state, which can enhance hydrogen donating ability and antioxidant properties of ascorbyl palmitate in bulk oils.

The results of this study clearly showed that mobility of hydrogens in antioxidants were influenced by the presence of phospholipids and affect solubility of antioxidants, which might help to explain synergistic and antagonistic effects of phospholipids.