The formation of cis-3-nonenal, trans-2-nonenal and hexanal from linoleic acid hydroperoxide isomers by a hydroperoxide cleavage enzyme system in cucumber (Cucumis sativus) fruits.
1. A particulate enzyme fraction and an acetone powder preparation from cucumber fruits cleaved 9- and 13-hydroperoxyoctadecadienoic acids to form volatile aldehydes and oxoacid fragments. 2. From the 9-hydroperoxide, the major volatile fragments were cis-3-nonenal and trans-2-nonenal using particulate enzyme and acetone powder preparations, respectively. 3. Hexanal was the only significant volatile fragment from the 13-hydroperoxide. 4. The particulate enzyme system was equally effective on both 9- and 13-hydroperoxide isomers and was fully active under anaerobic conditions and at pH 6.4. 5. An enzymic pathway for the biogenesis of hexanal, cis-3- and trans-2-nonenal (components of the characteristic flavour volatiles of cucumber) from linoleic acid is proposed. This involves the sequential activity of lipoxygenase, hydroperoxide cleavage and cis-3-: trans-2-enal isomerase enzymes.
D000447:Aldehydes; D002208:Caproates / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007651:Keto Acids / Q000378:metabolism; D008041:Linoleic Acids / Q000378:metabolism*; D010545:Peroxides / Q000378:metabolism; D010944:Plants / Q000201:enzymology*; D013237:Stereoisomerism; D013347:Subcellular Fractions / Q000201:enzymology
D000447:Aldehydes; D002208:Caproates; D007651:Keto Acids; D008041:Linoleic Acids; D010545:Peroxides; C013166:2-nonenal; C010463:n-hexanal