1-Octen-3-ol and 13-hydroperoxylinoleate are products of distinct pathways in the oxidative breakdown of linoleic acid by Pleurotus pulmonarius

The oxidative breakdown of linoleic acid leading to the formation of the mushroom flavor alcohol 1-octen-3-ol by mycelial homogenate of the edible mushroom Pleurotus pulmonarius grown in submerged culture was studied. The compounds 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid (13-HPOD) and 10-oxo-trans-8-decenoic acid (10-oxo-acid) were found to be the major nonvolatile metabolites associated with the enzymatic cleavage of linoleic acid to 1-octen-3-ol. Whereas 1-octen-3-ol and 10-oxo-acid were produced at all linoleic acid concentrations studied (up to 8 mM), 13-HPOD was absent at linoleic acid concentrations below 1 mM but became the major nonvolatile product of the enzymatic oxidation at concentrations above 1 mM. Despite its accumulation, 13-HPOD was found not to be the precursor of 1-octen-3-ol when it was supplied as the substrate instead of linoleic acid. Periodic addition of linoleic acid during the course of the reaction maintained 1-octen-3-ol formation at a constant rate while 13-HPOD accumulated, suggesting that 1-octen-3-ol formation may be limited by either competitive product inhibition or substrate availability. These results suggest the involvement of two different lipoxygenases in 1-octen-3-ol and 13-HPOD formation. Mild heat treatment of the pellets before homogenization and incubation completely inhibited 1-octen-3-ol formation and resulted in the accumulation of an additional HPOD, possibly a 1-octen-3-ol precursor. It would appear, therefore, that 13-HPOD accumulation takes place in parallel with 1-octen-3-ol and 10-oxo-acid biosynthesis, suggesting that these are two distinct biosynthetic pathways catalyzed by two different lipoxygenases.