Inhibition of linoleic acid oxidation by interaction with a protein-rich oat fraction

A protein-rich fraction from oat was found to protect linoleic acid against oxidation in an aqueous suspension containing soybean lipoxygenase-l and m icellar linoleic acid. In this system the oat. fraction reduced the initial oxidation rate of linoleic acid by 50% when the oat fraction/linoleic acid ratio was 5:1 (w/w). The oat fraction did not act on the lipoxygenase enzy me but reduced the concentration of linoleic acid that serves as a substrat e for lipoxygenase-l. To achieve the reduction in the oxidation rate a cont act between liaoleic acid and the oat fraction was required. The efficiency of the protection was dependent on the duration of this contact: the maxim um protection was reached after a 5-min incubation period. However, total c essation of oxidation was not; reached with any concentration of the oat fr action, indicating that the oxidizible and non-oxidizible forms of linoleic acid are in equilibrium. Because lipoxygenase-1 prefers the monomeric form of the substrate, the present findings agree with the hypothesis that the oat fraction reduces the concentration of monomolecular form of substrate. In most food systems monomolecular free linoleic acid is liberated slowly a nd at relatively low concentrations, therefore, even a small amount of the oat fraction would guard the system from oxidative deterioration.