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The extraction of 13-hydroperoxide-lyase activity from mint leaves as well as its use for C6-aldehyde production was studied in this work. The enzyme cleaves 13(S)-hydroperoxy-C18 fatty acids into C6-aldehyde and C12-oxo-acid. Two mint species were tested: Mentha veridis and Mentha pulegium. The headspace injection method coupled to gas chromatography was used for volatile compound analysis. The optimal conditions for temperature and pH were, respectively, 15 and 7 degrees C. We also studied the specific synthesis of hexanal and hexenals respectively from 13(S)-hydroperoxy-linoleic acid and 13(S)-hydroperoxy-linolenic acid. Considerable quantities of aldehyde (up to 2.58 micromol) were produced after 15 min of cleavage reaction in 2 ml stirred at 100 rpm, especially in presence of extract of M. veridis. The conversion yields decreased from 52.5% as maximum to 3.3% when using initial hydroperoxide concentrations between 0.2 and 15 mM. An unsaturated aldehyde, the 3(Z)-hexenal was produced from 13(S)-hydroperoxy-linolenic acid. The 3(Z)-isomer was unstable and isomerized in part to 2(E)-hexenal. In this work, we observed a very limited isomerization of 3(Z)-hexenal to 2(E)-hexenal, since the reaction and the volatile purge were carried out successively in the same flask without delay or any contact with the atmosphere. These aldehydes contribute to the fresh green odor in plants and are widely used in perfumes and in food technology. Their importance increases especially when the starting materials are of natural biological origin as used in this work. GC-MS analysis allowed the identification of the products.

The unsaturations and groups bound to the ring and to the lateral chain of lactones give a large diversity in this class of molecules. In this work we produced enzymatically a macrolactone in organic media. The substrate used was a hydroxy-fatty acid: (+)-coriolic acid and the enzymes tested were free or immobilized microbial lipases. The immobilized lipase from Candida antarctica seems to be the most adequate catalyst offering a high reaction yield. The intra-esterification was studied as a function of temperature and type of solvent. Higher yields were obtained when using diisopropyl-ether at 35 degrees C. This reaction, involving an alcohol group on an internal position on the carbon chain of the substrate hydroxy-acid, produces an original lactone: 13S-octadeca-(9Z,11E)-dienolide. The product was purified and characterized using (1)H nuclear magnetic resonance spectroscopy, mass spectrometry and infrared spectroscopy.

The biocatalysis of substrates in the gas phase may offer advantages over many conventional solution-based reactions, both in analytical devices and in bioreactors designed to accommodate this new technology. To date, however, the range of substrates for which gas-phase biocatalysis has been shown to be suitable is limited. Further research is required to establish the parameters that affect the kinetics and productivity of such systems.