Stabilization of an enzymatic extract from Penicillium camemberti containing lipoxygenase and hydroperoxide lyase activities

Recombinant Lipoxygenases and Hydroperoxide Lyases for the Synthesis of Green Leaf Volatiles

Green leaf volatiles (GLVs) are mainly C₆- and in rare cases also C₉-aldehydes, -alcohols, and -esters, which are released by plants in response to biotic or abiotic stresses. These compounds are named for their characteristic smell reminiscent of freshly mowed grass. This review focuses on GLVs and the two major pathway enzymes responsible for their formation: lipoxygenases (LOXs) and fatty acid hydroperoxide lyases (HPLs). LOXs catalyze the peroxidation of unsaturated fatty acids, such as linoleic and α-linolenic acids. Hydroperoxy fatty acids are further converted by HPLs into aldehydes and oxo-acids. In many industrial applications, plant extracts have been used as LOX and HPL sources. However, these processes are limited by low enzyme concentration, stability, and specificity. Alternatively, recombinant enzymes can be used as biocatalysts for GLV synthesis. The increasing number of well-characterized enzymes efficiently expressed by microbial hosts will foster the development of innovative biocatalytic processes for GLV production.

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

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.

Lyoprotection and stabilization of laccase extract from Coriolus hirsutus, using selected additives

The development of stable lyophilized laccase, obtained from Coriolus hirsutus, using a wide range of temperature treatments and storage conditions, was investigated. Using selected lyoprotectants, including, dextran 6 kDa, sucrose and a mixture of sodium benzoate, potassium sorbate and sorbitol (BKSS) (1.5:1.0:98.5; w/w/w) resulted by 2.4, 1.4 and 1.8-fold increase in laccase activity after lyophilization as compared to the fresh enzyme, respectively, whereas the addition of mannitol preserved 98.2% of its activity. Using 2.5% (w/v) dextran (15-25 kDa) or mannitol appeared to be the most appropriate lyoprotectants for the laccase activity. The laccase stability of the lyophilized enzymatic extract was greatly enhanced with the presence of mannitol, with 96.2, 38.9 and 24.7% of residual activity after 4 weeks of storage at - 80, 4 and 25 °C, respectively. The inactivation constant (k_inactivation) value and the amount required to decrease 50% of the laccase activity (C_1/2) showed that Carbowax^® polyethylene glycol (PEG)-8000 was the most appropriate additive for laccase activity, followed by glycerol and CuSO₄. When the enzymatic extract was incubated at 50 °C in the presence of either CuSO₄, PEG-8000 or glycerol, the time required to decrease 50% of the laccase initial activity (t₅₀), were 52.9, 54.6, 50.2 h, respectively, as compared to that of the control trial of 38.9 h.

Stability of hydroperoxide lyase activity from Amaranthus tricolor (Amaranthus mangostanus L.) leaves: influence of selected additives

BACKGROUND

Hydroperoxide lyase (HPL) has potential value for the flavour additive industry. Currently, the production and application of HPL suffer from stability problems. The objective of this study was to investigate the stabilisation of HPL preparation from Amaranthus tricolor leaves by the addition of selected chemical additives.

RESULTS

Amaranthus tricolor leaves were identified as a particularly rich source of 13-HPL activity. The addition of 100 g L(-1) sucrose and trehalose to microsomal HPL prior to lyophilisation could retain nearly 100% enzymatic activity, compared to only 20% for the lyophilised control. The lyophilised microsomal HPL containing sucrose maintained full activity for even 40 days storage at -20 degrees C. For HPL solution, glycerol was effective for long-term stability at -20 degrees C. Moreover, poyols (sucrose and trehalose) and amino acid (glycine) enhanced the thermostability of HPL, while KCl and polyol mannitol decreased the thermostability of HPL.

CONCLUSION

The flavour-producing enzyme HPL, found in the leaves of Amaranthus tricolor, was stabilised by the addition of chemical additives.