Oxylipins and Green Leaf Volatiles: Application of Enzymes From Plant Origin to Produce Flavors and Antifungal Aldehydes

Recombinant enzymes present economic feasibility, high yields, consistency, a regular supply due to the absence of seasonal fluctuations, stability, and great catalytic activity. The sequences of plant enzymes are available or can be improved by mutagenesis, screening for optimizing process conditions, or protein engineering. Lipoxygenase (LOX), the enzyme that starts the oxylipin synthesis pathway, catalyzes the site-specific oxygenation of linoleic (C18:2) and linolenic acids (C18:3), leading to 9- or 13-hydroperoxide derivatives. These reactive molecules are converted into a series of oxylipins by the catalytic activity of enzymes belonging to different oxylipin branches downstream to LOX. The hydroperoxide lyase (HPL) pathway produces short-chain volatile aldehydes that provide the fresh, green flavor in fruits and vegetables, and to other defense-related compounds. 13-LOX and 13-HPL are localized in plastids, contributing to the synthesis of short aldehydes and colnelenic acid. The aldehydes, products of the HPL pathway, are involved in plant defense as signalling molecules and as compounds with antiinsect and fungal activity. 9-LOX and 9/13-HPL localized in microsomes and lipid bodies act in tandem in the pathway, producing short aldehydes (hexanal, nonenal) and alcohols. These compounds can be used as flavoring agents to restore the natural freshness of food products. C6- and C9 aldehydes can be applied as mite antifeedants and in the control of mycotoxigenic fungi. In this chapter, the production of green leaf volatiles (GLVs) is reviewed. The opportunities of nanotechnology to stabilize and exploit enzymatic activities to produce GLVs and flavors are discussed.