[Progress report. Lipoxygenases--their significance in lipid chemistry]

Lipoxygenase catalysed reactions play an important role in the field of lipid peroxidation. The enzyme is characterized concerning its sources, biological importance, isolation, substrates, active centre and inhibition. Extensive explanations should show the complex mechanisms of enzyme catalyses divided into two major ways: dioxygenase and hydroperoxidase reactions. Food science specific importance and expected effects on food systems are discussed and related to reaction products generated during catalysis and enzymatic processes both preceding and following lipoxygenase reaction.

[On characterization of lipoxygenase from barley (author's transl)]

Lipoxygenase from brewing barley of Nordbaden has optimum activity at alkaline pH and predominantly forms 9-hydroperoxy-10-trans, 12-cis-octadecadienoic acid (9-LHPO) from linoleic acid. While at pH 7 90% 9-LHPO is produced, its proportions drops during incubation at more alkaline pH (pH 7,75) to 70%. This positional specifity is not caused by isoenzymes. While linoleic acid methylester is converted only to a lesser degree, trilinolein is not accepted as substrate.

Biochemistry of lipoxygenase in relation to food quality

A renewed interest in lipoxygenase has led to detailed studies of its isoenzymes, substrate specificity, and the nature of its reaction products. Lipoxygenase is highly specific for cis,cis-1,4-pentadiene systems such as linoleic, linolenic, and arachidonic acid (or ester) and catalyzes the formation of the corresponding hydroperoxides with a cis,-trans-conjugated diene system. The hydroperoxides can then undergo enzymic or spontaneous degradation, producing a range of carbonyl compounds. This review will discuss the biochemical properties of this enzyme and its contribution to the quality of raw and processed food products. An attempt has been made to discuss both the desirable and undesirable effects associated with the action of lipoxygenase, citing specific food examples where appropriate.

Conversion of linoleic acid hydroperoxide by soybean lipoxygenase in the presence of guaiacol: identification of the reaction products

Linoleic acid hydroperoxide formed by soybean lipoxygenase was metabolized by the same enzyme in the presence of guaiacol. The products of this reaction included, trihydroxyoctadecenoic acids, hydroperoxydihydroxyoctadecenoic acids, hydroxyepoxyoctadecenoic acids, dihydroxyoctadecenoic acids, hydroxyoctadecadienoic acids, and oxooctadecadienoic acids.