Volatile lipid oxidation products.

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.

Biochemistry of lipoxygenase in relation to food quality.

Changes in lipids and volatile compounds of oat flours and extrudates during processing and storage

A mixture of positional isomers of linoleic acid hydroperoxide was produced from the oxidation of linoleic acid by lipoxygenase from corn or soybean. Chromatography on a column of silicic acid separated 13-hydroperoxy-11,9-octadecadienoic acid in 99+% purity from the mixture obtained by soybean lipoxygenase oxidation of linoleic acid. Attempts at isolation of pure 9-hydroperoxy-10,12-octadecadienoic acid from hydroperoxides obtained by corn lipoxygenase oxygenation of linoleic acid were partially successful with isolation of the 9-hydroperoxide in 97% purity.

Isolation of a pure isomer of linoleic acid hydroperoxide.

Linoleic acid was oxidized with a protein fraction from soya beans (25°C; 2 h), in which lipoxygenase and peroxydase activities occurred. The fatty acids formed were isolated and, after emulsification with a sugar ester, were evaluated for bitter taste. The main components of the bitter-tasting fraction was a mixture of 9.12.13-trihydroxyoctadec-10- and 9.10.13-trihydroxyoctadec-11-enoic acids. The taste threshold lies in the range 0.6–0.9 μmol/ml. Two further trihydroxy-acids and two oxodihydroxy-acids were also identified in the bitter-tasting fraction.

Enzymatic oxydation of linoleic acid: formation of bittertasting fatty acids.

Bei Haferenzym-Linolsaure-Incubationen wird durch Lipoxygenasekatalyse stark uberwiegend die 9-Hydroperoxyoctadecadiensaure (9-LHPO) gebildet. Daneben entsteht ein vergleichsweise geringer Anteil an 13-LHPO. Der sich anschliesende enzymatische (Lipoperoxidase, Isomerase) und nicht-enzymatische Abbau der beiden Hydroperoxide fuhrt zu einem hohen Anteil der aus der 9-LHPO gebildeten 9-Hydroxy-cis,trans-octadecadiensaure, 9-Hydroxy-cis-12,13-epoxy-trans-10-octadecensdure und 9, 12, 13-Trihydroxy-trans-10-octadecensaure.

Über die Bildung und den Abbau von Linolsäurehydroperoxiden in Cerealien Quantitative Bestimmung der Reaktionsprodukte

Mittels Gelchromatographie von Ammoniumsulfatpraparaten aus Hafer und Sojabohnen wurden jeweils zwei Proteinfraktionen mit gemeinsamer Lipoxygenase- und Linolsaurehydroperoxid-Abbau-Aktivitat erhalten. Beide Enzymkomplexe (I u. II) unterscheiden sich mit > 250000 (I) und 100000 (II) in ihrem Molekulargewicht. Das Aktivitatsverhaltnis Lipoxygenase zu “Lipoperoxidase” in II lag fur Hafer und Sojabohnen in der Grosenordnung von 30:1. Bei der isoelektrischen Fokussierung von II traten nach substratspezifischer Anfarbung bei Sojabohnen vier Banden im pH-Bereich von 5,65-5,80, bei Hafer eine Bande bei einem isoelektrischen Punkt von 5,70 auf. Das Vorliegen eines bifunktionellen Lipoxygenase- „Lipoperoxidase” Komplexes wird diskutiert.

Über das Lipoxygenase — „Lipoperoxidase” — System in Cerealien. Abtrennung von zwei Proteinkomplexen mit Lipoxygenase — und Linolsäurehydroperoxid-Abbau-Aktivität aus Hafer und Sojabohnen

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Über die Bildung und den Abbau von Linolsäurehydroperoxiden in Cerealien Quantitative Bestimmung der Reaktionsprodukte

Über das Lipoxygenase — „Lipoperoxidase” — System in Cerealien. Abtrennung von zwei Proteinkomplexen mit Lipoxygenase — und Linolsäurehydroperoxid-Abbau-Aktivität aus Hafer und Sojabohnen