Abstract
The autoxidation of soybean oil was effectively inhibited by the addition of a commercial free oxygen absorber (FOA) of the iron powder type into the headspace and/or oil phase in a flask closed with a rubber stopper. Increase in peroxide value (POV) during storage at room temperature for 4, 6 or 10 months was almost completely suppressed by FOA added to the headspace or both headspace and oil phase in a sealed flask (0.72.1 times that at the start). The decomposition of tocopherols (Toc) in soybean oils hardly occurred. POV of soybean oil, which is usuallypreserved in a flask (blank test), remarkably increased (20.8410.5 times that at the start), and Toc was reduced to about 40 % the initial level at 10 months of storage. On opening the sealed flask, can or bottle, the soybean oil preserved by FOA was found to be more resistant to autoxidation than new soybean oil not pretreated with FOA. The dissolved free oxygen in the oil is thus shown to substantially accelerate autoxidation. The preservation of soybean oil by FOA sealed with polyethylene (PE) film was assessed for the prevention of oil penetration into the absorber, since such penetration deactivates the absorber and may cause migration of iron and other substances from FOA into the oil. The addition of FOA sealed with PE film into the headspace of the flask inhibited increase in POV (to about 1/41/3 that of blank), but it was less active than that of the uncovered absorber (about 1/20 that of blank). The addition of FOA sealed with PE film to the oil phase in a sealed flask slightly depressed increase in POV (about 1/32/3 that of blank). The present results indicate FOA to be the quite effective for improving quality maintenance of edible oils.
