Role of moisture on the lipid oxidation determined by D(2)O in a linoleic acid model system

The possibility of moisture, as an active substance for lipid oxidation, was determined in linoleic acid model systems containing deuterium oxide (D2O) and deuterium free H2O, by measuring the headspace oxygen content and headspace volatiles. Mixtures of D2O and H2O, at the ratio of 3:0, 2:1, 1:2, and 0:3 (w/w), were added to linoleic acid and oxidised at 60°C. The existence of deuterium in headspace volatiles, was indirectly determined by comparing the amount of fragmented mass to charge ratio (m/z), which was 73.1/72.1 for d1-pentane/pentane, 57.0/56.0 for d1-2-propenal/2-propenal, 101.1/100.1 for d1-hexanal/hexanal, 113.1/112.1 for d1-t-2-heptenal-D/t-2-heptenal, and 153.2/152.2 for d1-2,4-decadieanl/2,4-decadieanl. As the oxidation time increased to 12h, the ratio of 73.1/72.1 (m/z) for pentane and 57.0/56.0 for 2-propenal increased significantly with a concentration dependent manner of deuterium oxide, which implies water was incorporated as a substrate during volatile formation. However, hexanal, t-2-heptenal, and 2,4-decadieanl did not follow the patterns of pentane and 2-propenal, implying that the formation mechanisms of these volatiles may not share the same pathways with pentane and 2-propenal. This study showed that moisture participates for the formation of volatiles and moisture may act as a substrate for lipid oxidation.