Evidence for the Occurrence of Lipoxygenase Activity in Grapes (Variety Carignane)

Evidence of lipoxygenase activity on grapes (variety Carignane) was obtained by four different methods: oxygen uptake enzymaticly catalyzed in the presence of linoleic acid; increase in absorbance at 234 nm by the action of a partially purified enzyme on linoleic acid; inhibition studies by elaidolinoleic acid and cyanide ions; and isolation and identification of isomeric hydroperoxides by HPLC and GC-MS. The results obtained by HPLC show that, after the action of grape enzymes on linoleic acid, 80% of 13-hydroperoxides and 20% of 9-hydroperoxides are formed. These results agree with the formation of C₆ aldehydes and alcohols from C18-hydroperoxides. Hypotheses concerning the destiny of 9-hydroperoxides are discussed.