Hydroperoxide lyase from olive (Olea europaea) fruits

Hydroperoxide lyase catalyses the cleavage of hydroperoxides from polyunsaturated fatty acids to yield oxoacids and volatile aldehydes. Some of these aldehydes are constituents of the aroma of many fruits and vegetables, and are the major components of the aroma of virgin olive oil. The enzyme has been extracted by solubilization of membrane fractions prepared from the pulp tissues of developing olive fruits. Partial purification by ion-exchange and hydroxyapatite chromatography resulted in the resolution of two isoforms of the enzyme of similar properties: both showed optimal pH at 6.0 and were active with 13-fatty acid hydroperoxides only. The activity measured with 13-EZZ-hydroperoxy-linolenate was 2.5-fold higher than that measured with 13-EZ-hydroperoxylinoleate. Both enzymes showed high affinity for 13-hydroperoxides, with K-m values in the micromolar range. The involvement of this enzyme activity in the formation of volatile aldehydes, present in the aroma of olive oil, is discussed. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.