Laccases in Food Industry: Bioprocessing, Potential Industrial and Biotechnological Applications

Laccases as green and versatile biocatalysts: from lab to enzyme market-an overview

Laccases are multi-copper oxidase enzymes that catalyze the oxidation of different compounds (phenolics and non-phenolics). The scientific literature on laccases is quite extensive, including many basic and applied research about the structure, functions, mechanism of action and a variety of biotechnological applications of these versatile enzymes. Laccases can be used in various industries/sectors, from the environmental field to the cosmetics industry, including food processing and the textile industry (dyes biodegradation and synthesis). Known as eco-friendly or green enzymes, the application of laccases in biocatalytic processes represents a promising sustainable alternative to conventional methods. Due to the advantages granted by enzyme immobilization, publications on immobilized laccases increased substantially in recent years. Many patents related to the use of laccases are available, however, the real industrial or environmental use of laccases is still challenged by cost-benefit, especially concerning the feasibility of producing this enzyme on a large scale. Although this is a compelling point and the enzyme market is heated, articles on the production and application of laccases usually neglect the economic assessment of the processes. In this review, we present a description of laccases structure and mechanisms of action including the different sources (fungi, bacteria, and plants) for laccases production and tools for laccases evolution and prediction of potential substrates. In addition, we both compare approaches for scaling-up processes with an emphasis on cost reduction and productivity and critically review several immobilization methods for laccases. Following the critical view on production and immobilization, we provide a set of applications for free and immobilized laccases based on articles published within the last five years and patents which may guide future strategies for laccase use and commercialization.

Laccase as a Tool in Building Advanced Lignin-Based Materials

Lignin is an abundant natural feedstock that offers great potential as a renewable substitute for fossil-based resources. Its polyaromatic structure and unique properties have attracted significant research efforts. The advantages of an enzymatic over chemical or thermal approach to construct or deconstruct lignins are that it operates in mild conditions, requires less energy, and usually uses non-toxic chemicals. Laccase is a widely investigated oxidative enzyme that can catalyze the polymerization and depolymerization of lignin. Its dual nature causes a challenge in controlling the overall direction of lignin-laccase catalysis. In this Review, the factors that affect laccase-catalyzed lignin polymerization were summarized, evaluated, and compared to identify key features that favor lignin polymerization. In addition, a critical assessment of the conditions that enable production of novel lignin hybrids via laccase-catalyzed grafting was presented. To assess the industrial relevance of laccase-assisted lignin valorization, patented applications were surveyed and industrial challenges and opportunities were analyzed. Finally, our perspective in realizing the full potential of laccase in building lignin-based materials for advanced applications was deduced from analysis of the limitations governing laccase-assisted lignin polymerization and grafting.

Review of advances in the development of laccases for the valorization of lignin to enable the production of lignocellulosic biofuels and bioproducts

Development and deployment of commercial biorefineries based on conversion of lignocellulosic biomass into biofuels and bioproducts faces many challenges that must be addressed before they are commercially viable. One of the biggest challenges faced is the efficient and scalable valorization of lignin, one of the three major components of the plant cell wall. Lignin is the most abundant aromatic biopolymer on earth, and its presence hinders the extraction of cellulose and hemicellulose that is essential to biochemical conversion of lignocellulose to fuels and chemicals. There has been a significant amount of work over the past 20 years that has sought to develop innovative processes designed to extract and recycle lignin into valuable compounds and help reduce the overall costs of the biorefinery process. Due to the complex matrix of lignin, which is essential for plant survival, the development of a reliable and efficient lignin conversion technology has been difficult to achieve. One approach that has received significant interest relies on the use of enzymes, notably laccases, a class of multi‑copper green oxidative enzymes that catalyze bond breaking in lignin to produce smaller oligomers. In this review, we first assess the different innovations of lignin valorization using laccases within the context of a biorefinery process, and then assess the latest economical advances that these innovations offered. Finally, we review laccase characterization and optimization, as well as the prospects and bottlenecks of this class of enzymes within the industrial and biorefining sectors.

High-level synthesis and secretion of laccase, a metalloenzyme biocatalyst, by the halophilic archaeon Haloferax volcanii

Haloarchaea and their enzymes have extremophilic properties desirable for use as platform organisms and biocatalysts in the bioindustry. These GRAS (generally regarded as safe) designated microbes thrive in hypersaline environments and use a salt-in strategy to maintain osmotic homeostasis. This unusual strategy has resulted in the evolution of most of the intracellular and extracellular enzymes of haloarchaea to be active and stable not only in high salt (2-5M) but also in low salt (0.2M). This salt tolerance is correlated with a resilience to low water activity, thus, rendering the haloarchaeal enzymes active and stable in organic solvent and temperatures of 50-60°C used in the enzymatic biodelignification and saccharification of lignocellulosic materials. High-level secretion of haloarchaeal enzymes to the extracellular milieu is useful for many applications, including enzymes that deconstruct biomass to allow for lignin depolymerization and simultaneous fermentation of sugars released from hemicellulose and cellulose fractions of lignocellulosics. Here we detail strategies and methods useful for high-level secretion of a laccase, HvLccA, that mediates oxidation of various phenolics by engineering a recombinant strain of the haloarchaeon Haloferax volcanii.

Efficient decolorization of recalcitrant dyes at neutral/alkaline pH by a new bacterial laccase-mediator system

Laccases and laccase-mediator systems (LMS) are versatile catalysts that can oxidize a broad range of substrates coupled to the sole reduction of dioxygen to water. They possess many biotechnological applications in paper, textile, and food industries, bioethanol production, organic synthesis, detection and degradation of pollutants, and biofuel cell development. In particular, bacterial laccases are getting relevance due to their activity in a wide range of pH and temperature and their robustness under harsh conditions. However, the enzyme and the redox mediator's availability and costs limit their large-scale commercial use. Here we demonstrate that β-(10-phenothiazyl)-propionic acid can be used as an efficient and low-cost redox mediator for decolorizing synthetic dyes by the recombinant laccase SilA from Streptomyces ipomoeae produced in E. coli. This new LMS can decolorize more than 80% indigo carmine and malachite green in 1 h at pH = 8.0 and 2 h in tap water (pH = 6.8). Furthermore, it decolorized more than 40% of anthraquinone dye remazol brilliant blue R and 80% of azo dye xylidine ponceau in 5 h at 50 °C, pH 8.0. It supported at least 3 decolorization cycles without losing activity, representing an attractive candidate for a cost-effective and environmentally friendly LMS functional at neutral to alkaline pH.

Advances in laccase-triggered anabolism for biotechnology applications

This is the first comprehensive overview of laccase-triggered anabolism from fundamental theory to biotechnology applications. Laccase is a typical biological oxidordeuctase that induces the one-electronic transfer of diverse substrates for engendering four phenoxy radicals with concomitant reduction of O₂ into 2H₂O. In vivo, laccase can participate in anabolic processes to create multifarious functional biopolymers such as fungal pigments, plant lignins, and insect cuticles, using mono/polyphenols and their derivatives as enzymatic substrates, and is thus conducive to biological tissue morphogenesis and global carbon storage. Exhilaratingly, fungal laccase has high redox potential (E° = 500-800 mV) and thermodynamic efficiency, making it a remarkable candidate for utilization as a versatile catalyst in the green and circular economy. This review elaborates the anabolic mechanisms of laccase in initiating the polymerization of natural phenolic compounds and their derivatives in vivo via radical-based self/cross-coupling. Information is also presented on laccase immobilization engineering that expands the practical application ranges of laccase in biotechnology by improving the enzymatic catalytic activity, stability, and reuse rate. Particularly, advances in biotechnology applications in vitro through fungal laccase-triggered macromolecular biosynthesis may provide a key research direction beneficial to the rational design of green chemistry.

Enzyme Activities of Five White-Rot Fungi in the Presence of Nanocellulose

White-rot fungi can degrade all lignocellulose components due to their potent lignin and cellulose-degrading enzymes. In this study, five white-rot fungi, Trametes versicolor, Trametes pubescens, Ganoderma adspersum, Ganoderma lipsiense, and Rigidoporus vitreus were tested for endoglucanase, laccase, urease, and glucose-6-phosphate (G6P) production when grown with malt extract and nanocellulose in the form of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidized cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC). Results show that temperature plays a key role in controlling the growth of all five fungi when cultured with malt extract alone. Endoglucanase activities were highest in cultures of G. adspersum and G. lipsiense and laccase activities were highest in cultures of T. versicolor and R. vitreus. Urease activities were highest in cultures of G. adspersum, G. lipsiense, and R. vitreus. Glucose-6-phosphate levels also indicate that cells were actively metabolizing glucose present in the cultures. These results show that TEMPO-oxidized CNF and CNC do not inhibit the production of specific lignocellulose enzymes by these white-rot fungi. The apparent lack of enzymatic inhibition makes TEMPO-oxidized CNF and CNC excellent candidates for future biotechnological applications in combination with the white-rot fungi studied here.

Bio Efficacy Assay of Laccase Isolated and Characterized from Trichoderma viride in Biodegradation of Low Density Polyethylene (LDPE) and Textile Industrial Effluent Dyes

This study is based on the biosynthesis of laccase enzyme from fungi Trichoderma viride and its exploitation in biodegradation of polyethylene using Laccase mediator system (LMS -Laccase + 1-HBT) in Low Density Polyethylene (LDPE) and in biodegradation of textile industrial effluent dyes. In different parts of our lifespan we have seen the numerous types of plastics are getting degraded by various methods, still the average time to completely degrade a plastic bottle is at least 450 years.Similarly industry produces over 3.6 thousand individual textile dyes today and utilizes more than 8000 toxic chemicals in numerous methods for textile manufacture comprising dyeing and printing. As polyethylene and textile industrial effluent dyes are causing severe hazardous effect on environment and health issues in all kind of living organisms, it is necessary to degrade plastics and textile industrial effluent dyes in rapid way. Recently researchers have come up with an idea of degrading plastic and textile industrial effluent dyes with the help of microorganisms and enzymes much faster than normal rate. The Laccase enzyme extracted was tested for its optimum temperature and pH. Lowry’s method is used for protein estimation. A control and sample LDPE was subjected to LMS. The tensile strength and elongation of the sample was less than that of the control after 5 days of treatment. This study showed that laccase together with 1-HBT helps to biodegrade polyethylene. The purified laccase enzyme was used for the pretreatment assay and post treatment assay. The Laccase degrades certain reactive dyes like Congo red, Acid Red, Methylene Blue, Brilliant Blue, Metallic Blue and Black. Thus recommends the application of laccase in textile dye colour removal (bioremediation).

Biogenic manganese oxides combined with 1-hydroxybenzotriazol and an Mn(II)-oxidizing enzyme from Pleosporales sp. Mn1 oxidize 3,4-dimethoxytoluene to yield 3,4-dimethoxybenzaldehyde

Using soil samples, we screened for microbes that produce biogenic manganese oxides (BMOs) and isolated Mn(II)-oxidizing fungus, namely Pleosporales sp. Mn1 (Mn1). We purified the Mn(II)-oxidizing enzyme from intracellular extracts of Mn1. The enzyme oxidized Mn(II) most effectively at pH 7.0 and 45 °C. The N-terminal amino acid sequence of the purified enzyme possessed homology with multicopper oxidases in fungi. The properties of the enzyme and the effects of the pH and inhibitors on the Mn(II)-oxidization activity suggested that the enzyme is a member of the multicopper oxidase family. The X-ray diffraction pattern of the BMOs produced by Mn1 showed a strong correlation with that of a typical poorly crystalized vernadite (δ-MnO₂). Since BMOs are some of the most reactive materials in the environment, we investigated a potential new application of BMOs as oxidation catalysts. We confirmed that BMOs oxidized aromatic methyl groups when combined with the purified enzyme and a mediator, 1-hydroxybenzotriazole (HBT). BMO oxidation of 3,4-dimethoxytoluene achieved a better yield than that of abiotic MnO₂ and white-rot fungus laccase under acidic and neutral pH conditions. Under neutral pH, the BMOs oxidized 3,4-dimethoxytoluene to yield 200-fold more 3,4-dimethoxybenzaldehyde than that of abiotic MnO₂. This is the first report to reveal that BMOs combined with a Mn(II)-oxidizing enzyme and mediator can oxidize aromatic hydrocarbons to yield corresponding aldehydes.