Enzymatic depolymerization of industrial lignins by laccase‐mediator systems in 1,4‐dioxane/water

Abstract

Lignin is the second most abundant polymer after cellulose in lignocellulosic biomass. Its aromatic composition and recalcitrant nature make its valorization a major challenge for obtaining low molecular weight aromatics compounds with high value-added from the enzymatic depolymerization of industrial lignins. The oxidation reaction of lignin polymer using laccases alone remains inefficient. Therefore, researches are focused on the use of a laccase-mediator system (LMS) to facilitate enzymatic depolymerization. Until today, the LMS system was studied using water-soluble lignin only (commercial lignins, modified lignins, or lignin model compounds). This work reports a study of three LMS systems to depolymerize the three major industrial lignins (organosolv lignin, Kraft lignin, and sodium lignosulfonate). We show that an enzymatic depolymerization of these lignins can be achieved by LMS using laccase from Trametes versicolor, 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt as mediator and a cosolvent (25% of 1,4-dioxane) to enhance the solubilization of lignins. C 2020

Laccase as a Tool in Building Advanced Lignin‐Based Materials

“…[57] Similarly, this limitation in solubility is reflected in laccase-lignin catalysis as early studies of this system have been broadly investigated but limited to water-soluble lignin, modified lignin, or lignin model compounds. [58] Whether the final aim is to polymerize or depolymerize lignin, the solubility of the starting lignin in the reaction medium is an important factor to consider for successful laccase catalysis. For example, Mattinen et al [59] studied the oxidative polymerization of three different technical lignins by a high-redox-potential Trametes hirsuta laccase (ThL).…”

“…It has to be noted that in many other reports, depolymerization was the dominant outcome of lignin incubation in laccase‐mediator systems. [ 5 , 49a , 58 , 76 ] However, the aim of those studies was to deconstruct lignin structure into small aromatic molecules, which is not covered by this Review.…”

“…High degree of polymerization of the lignin substrate and the low redox potential of laccase enzymes usually requires their combination with mediators for efficiently enabling substrate oxidations. [ 45 , 49a , 58 ] However, certain mediators, especially the synthetic ones, are expensive, toxic, and might cause a certain degree of laccase deactivation. [ 5 , 16b ] Obviously, prompting lignin valorization by treatment with laccases should also consider production of efficient and compatible mediators.…”

Biofuels Production from Renewable Resources

“…Dillies et al. [8] reported on three Lac‐mediator systems (LMSs) to depolymerize the major industrial lignins (organosolv lignin, Kraft lignin, and sodium lignosulfonate). Their data show that enzymatic depolymerization of these lignins can be achieved by LMS using Lac from Trametes versicolor , a mediator, and a cosolvent to enhance the solubilization of lignins.…”

Electro-oxidative depolymerisation of technical lignin in water using platinum, nickel oxide hydroxide and graphite electrodes

“…4 In the literature, numerous studies propose several interesting approaches for lignin upgrading, such as pyrolysis, enzymatic or chemical depolymerisation and surface functionalisation. [5][6][7][8][9] However, most of them require harsh reaction conditions, such as high temperature, high pressure, expensive and hazardous catalysts which make the process not economically viable on a larger scale. 10 The electrochemical depolymerisation of lignin, especially if powered by renewable electricity, is a promising technology compared to conventional chemical oxidation because it can operate under mild, safe and eco-friendly reaction conditions, such as room temperature and atmospheric pressure.…”