Biocatalytic Synthesis of Natural Green Leaf Volatiles Using the Lipoxygenase Metabolic Pathway

Abstract

In higher plants, the lipoxygenase enzymatic pathway combined actions of several enzymes to convert lipid substrates into signaling and defense molecules called phytooxylipins including short chain volatile aldehydes, alcohols, and esters, known as green leaf volatiles (GLVs). GLVs are synthesized from C18:2 and C18:3 fatty acids that are oxygenated by lipoxygenase (LOX) to form corresponding hydroperoxides, then the action of hydroperoxide lyase (HPL) produces C6 or C9 aldehydes that can undergo isomerization, dehydrogenation, and esterification. GLVs are commonly used as flavors to confer a fresh green odor of vegetable to perfumes, cosmetics, and food products. Given the increasing demand in these natural flavors, biocatalytic processes using the LOX pathway reactions constitute an interesting application. Vegetable oils, chosen for their lipid profile are converted in natural GLVs with high added value. This review describes the enzymatic reactions of GLVs biosynthesis in the plant, as well as the structural and functional properties of the enzymes involved. The various stages of the biocatalytic production processes are approached from the lipid substrate to the corresponding aldehyde or alcoholic aromas, as well as the biotechnological improvements to enhance the production potential of the enzymatic catalysts.

Bioactive (Poly)phenols, Volatile Compounds from Vegetables, Medicinal and Aromatic Plants

“…( E )-2-nonenal and ( Z )-3-hexenal ( Figure 12 ), despite their different structures, also originate from different fatty acids (( E )-2-nonenal, from linoleic acid and ( Z )-3-hexenal from linolenic acid) and are described as presenting other sensory attributes. “Penetrating”, “waxy” [ 150 ] or “fatty” [ 152 ] characteristics have been linked to ( E )-2-nonenal, while, for ( Z )-3-hexenal, “leafy”, “powerful”, “strawberry leaf”, “winey”, “green leaves”, “apple-like”, “leaf-like” and “cut grass” attributes have also been linked.…”

“…(E)-2-Nonenal and Hexenal (Figure 12), despite their different structures, also originate from differe acids ((E)-2-Nonenal, from linoleic acid and (Z)-3-Hexenal from linolenic acid) a described as presenting other sensory attributes. "Penetrating", "waxy" [150] or [152] characteristics have been linked to (E)-2-Nonenal, while, for (Z)-3-Hexenal, " "powerful", "strawberry leaf", "winey", "green leaves", "apple-like", "leaf-like" a grass" attributes have also been linked. Volatile aldehydes, also a chemical class formed by the lipoxygenase pathway from fatty acids [139,149], are well-known for their green note odour.…”

Optimizing the Production of Recombinant Hydroperoxide Lyase in Escherichia coli Using Statistical Design

“…In this pathway, LOX first catalyzes the oxygenation of polyunsaturated fatty acids (PUFAs), such as linoleic or α-linolenic acids, to produce corresponding hydroperoxides [4,13,14]. Subsequently, HPL acts on these PUFA hydroperoxides to form volatile short-chain aldehydes (C 6 or C 9 -aldehydes) and ω-oxoacids [6,[15][16][17][18][19]. HPLs are heme enzymes belonging to the cytochrome P450 family and are divided into two subfamilies by their substrate specificities, namely CYP74B for 13-HPLs and CYP74C for 9-HPLs and 9/13-HPLs.…”

“…The industrial production of GLVs by chemical synthesis is environmentally unfriendly, and nowadays, consumers have a strong preference for naturally synthesized additives and flavors. Given the high demand for such natural flavors and the low yield of extracting the compounds directly from plants, efficient biocatalytic processes using the enzymes of the LOX pathway are developed [19,32]. In these processes, vegetal oils are hydrolyzed by lipase, and then the PUFAs released are converted by LOX and HPL into green note aldehydes [23,[33][34][35][36].…”

“…In these processes, vegetal oils are hydrolyzed by lipase, and then the PUFAs released are converted by LOX and HPL into green note aldehydes [23,[33][34][35][36]. Since lipases and LOXs are commercially available, genetic engineering approaches focus on the production of recombinant HPL [19,[37][38][39][40][41].…”