Continuous enzymatic esterification of glycerol with (poly)unsaturated fatty acids in a packed-bed reactor

Tri-enzyme fusion of tryptophan halogenase achieves a concise strategy for coenzyme self-sufficiency and the continuous halogenation of L-tryptophan

The halogenase-based catalysis is one of the most environmentally friendly methods for the synthesis of halogenated products, among which flavin-dependent halogenases (FDHs) have attracted great interest as one of the most promising biocatalysts due to the remarkable site-selectivity and wide substrate range. However, the complexity of constructing the NAD+-NADH-FAD-FADH2 bicoenzyme cycle system has affected the engineering applications of FDHs. In this work, a coenzyme self-sufficient tri-enzyme fusion was constructed and successfully applied to the continuous halogenation of L-tryptophan. SpFDH was firstly identified derived from Streptomyces pratensis, a highly selective halogenase capable of generating 6-chloro-tryptophan from tryptophan. Then, using gene fusion technology, SpFDH was fused with glucose dehydrogenase (GDH) and flavin reductase (FR) to form a tri-enzyme fusion, which increased the yield by 1.46-fold and making the coenzymes self-sufficient. For more efficient halogenation of L-tryptophan, a continuous halogenation bioprocess of L-tryptophan was developed by immobilizing the tri-enzyme fusion and attaching it to a continuous catalytic device, which resulted in a reaction yield of 97.6% after 12 h reaction. An FDH from S. pratensis was successfully applied in the halogenation and our study provides a concise strategy for the preparation of halogenated tryptophan mediated by multienzyme cascade catalysis.

Esters in the Food and Cosmetic Industries: An Overview of the Reactors Used in Their Biocatalytic Synthesis

Esters are versatile compounds with a wide range of applications in various industries due to their unique properties and pleasant aromas. Conventionally, the manufacture of these compounds has relied on the chemical route. Nevertheless, this technique employs high temperatures and inorganic catalysts, resulting in undesired additional steps to purify the final product by removing solvent residues, which decreases environmental sustainability and energy efficiency. In accordance with the principles of "Green Chemistry" and the search for more environmentally friendly methods, a new alternative, the enzymatic route, has been introduced. This technique uses low temperatures and does not require the use of solvents, resulting in more environmentally friendly final products. Despite the large number of studies published on the biocatalytic synthesis of esters, little attention has been paid to the reactors used for it. Therefore, it is convenient to gather the scattered information regarding the type of reactor employed in these synthesis reactions, considering the industrial field in which the process is carried out. A comparison between the performance of the different reactor configurations will allow us to draw the appropriate conclusions regarding their suitability for each specific industrial application. This review addresses, for the first time, the above aspects, which will undoubtedly help with the correct industrial implementation of these processes.

Sustainable synthesis of branched-chain diesters

Esters from branched alcohols and dicarboxylic linear acids are widely used as lube bases due to their good performance at low temperatures. This work proposes a new process to synthesize bis(2-ethylbutyl) adipate and bis(2-ethylbutyl) sebacate by using the lipase-based catalyst Novozym® 435 in a solvent-free system. Different reaction strategies have been tested in order to minimize 2-ethyl-1-butanol losses due to its evaporation and optimum operation conditions have been determined: 2.5 % of biocatalyst, 50 °C and a molar excess of alcohol of 15 % for the adipic diester and of 25 % for the sebacic one. It has also been proven that the immobilized enzyme can be reused in seven successive reaction cycles, achieving high yields without an appreciable reduction of activity. This biocatalytic pathway is a promising basis for the development of a more sustainable large scale process for obtaining biodegradable lubricants, as it is pointed out by productivity, economic and green metrics calculations.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Highly Selective Synthesis of Monolaurin via Enzymatic Transesterification under Batch and Continuous Flow Conditions

This study aimed to investigate the highly selective production of monolaurin via enzymatic transesterification of methyl laurate and glycerol. It was determined that a binary solvent system (tert-butanol/iso-propanol, 20:80, wt./wt.) was suitable for the enzymatic production of monolaurin, especially in the continuous process. The highest mass fraction of monolaurin in the product mixture (80.8 wt.%) was achieved in a batch mode under the following conditions: a methyl laurate-to-glycerol molar ratio of 1:6, a substrate concentration (methyl laurate in the binary solvent) of 15 wt.%, an enzyme dosage of 6 wt.% of the amount of methyl laurate, and a reaction time of 1.5 h at 50°C. Compared with the results under the batch conditions, a slightly higher yield of monolaurin (82.5 ± 2.5 wt.%) was obtained in a continuous flow system at a flow rate of 0.1 mL/min, while the mass fraction of dilaurin in the product mixture was only 0.7 ± 0.6 wt.%. In addition, the yield of monolaurin remained almost unchanged during the 18 tested days of the continuous experiment.

From batch to fed-batch and to continuous packed-bed reactors: Lipase-catalyzed esterifications in low viscous deep-eutectic-solvents with buffer as cosolvent

This work explores for the first time the use of Deep Eutectic Solvents (DES) with phosphate buffer 100 mM pH 7 as cosolvent (10% v/v) in biocatalytic reactions in fed-batch and packed-bed bioreactors. The lipase-catalyzed esterification of glycerol and benzoic acid is studied, as it involves two substrates with different polarities (for which DES are needed). In the fed-batch bioreactor, the highest conversion (90%) was obtained at a substrate flow rate of 0.01 mL/min. The fed-batch operation increased the conversion by 59% compared to the batch mode. Regarding productivity, semi-continuous and continuous bioreactors showed analogous results. Upon recirculation of the reaction media in the continuous bioreactor, a conversion of 67% was achieved in 7 cycles of operation. The stability of the biocatalyst in the packed-bed bioreactor decreased only 2% in 10 days, demonstrating the attractiveness that low viscous DES-water mixtures with continuous processes may have.

Multienzyme mevalonate pathway bioreactor

The five-carbon metabolic intermediate isopentenyl diphosphate constitutes the basic building block for the biosynthesis of all isoprenoids in all forms of life. Two distinct pathways lead from amphibolic intermediates to isopentenyl diphosphate. The Gram-positive cocci and certain other pathogenic bacteria employ exclusively the mevalonate pathway, a set of six enzyme-catalyzed reactions that convert 3 mol of acetyl-CoA to 1 mol each of carbon dioxide and isopentenyl diphosphate. The survival of the Gram-positive cocci requires a fully functional set of mevalonate pathway enzymes. These enzymes therefore represent potential targets of inhibitors that might be employed as antibiotics directed against multidrug-resistant strains of certain bacterial pathogens. A rapid throughput, bioreactor-based assay to assess the effects of potential inhibitors on several enzymes simultaneously should prove useful for the survey of candidate inhibitors. To approach this goal, and as a proof of concept, we employed enzymes from the Gram-positive pathogen Enterococcus faecalis. Purified recombinant enzymes that catalyze the first three reactions of the mevalonate pathway were immobilized in two kinds of continuous flow enzyme bioreactors: a classical hollow fiber bioreactor and an immobilized plug flow bioreactor that exploited a novel method of enzyme immobilization. Both bioreactor types employed recombinant acetoacetyl-CoA thiolase, HMG-CoA synthase, and HMG-CoA reductase from E. faecalis to convert acetyl-CoA to mevalonate, the central intermediate of the mevalonate pathway. Reactor performance was monitored continuously by spectrophotometric measurement of the concentration of NADPH in the reactor effluent. Additional potential applications of an Ni(++) affinity support bioreactor include using recombinant enzymes from extremophiles for biosynthetic applications. Finally, linking a Ni(++) affinity support bioreactor to an HPLC-mass spectrometer would provide an experimental and pedagogical tool for study of metabolite flux and pool sizes of intermediates to model regulation in intact cells.