Enzymatic catalysis in microreactors has attracted growing scientific interest because of high specific surface enabling heat and mass transfer and easier control of reaction parameters in microreactors. However, two major challenges that limit their application are fast inactivation and the inability to the biocatalysts in microchannel reactors. A fluid and unsinkable immobilized enzyme were firstly applied in a microchannel reactor for biocatalysis in this study. Functionalized forms of graphene-immobilized naringinase flowing in microchannels have yielded excellent results for isoquercitrin production. A maximum yield of 92.24 ± 3.26% was obtained after 20 min in a microchannel reactor. Ten cycles of enzymatic hydrolysis reaction were successively completed and an enzyme activity above 85.51 ± 2.76% was maintained. The kinetic parameter V m/K m increased to 1.9-fold and reaction time was decreased to 1/3 compared with that in a batch reactor. These results indicated that the moving and unsinkable graphene sheets immobilized enzyme with a high persistent specificity and a mild catalytic characteristic enabled the repetitive use of enzyme and significant cost saving for the application of enzyme catalysis. Thus, the developed method has provided an efficient and simple approach for the productive and repeatable microfluidic biocatalysis.

BACKGROUNDWhole‐cell catalysis has been widely used because the steps of extracting pure enzyme are omitted and the cost would be greatly saved. However, the efficiency of the whole‐cell catalyst can be limited by the existence of the cell membrane. In the present study, to enhance the binding between an intracellular enzyme and a substrate, ionic liquids (ILs) and deep eutectic solvents (DESs) were used to treat Escherichia coli BL21‐pET21a‐rhaB1 cells for isoquercitrin production by the biotransformation of rutin.RESULTSThe whole‐cell catalyst exhibited the highest catalytic activity with 6% choline chloride‐urea (ChCl/U) after treatment with different concentrations. The ChCl/U‐treated whole‐cell catalyst was more stable than the crude rhaB1, because its optimum pH was closer to neutral and it demonstrated higher temperature tolerance. Under the best conditions of rutin concentration 0.05 g L–1, pH 6.5 and 40 °C, the isoquercitrin yield reached a maximum of 93.05 ± 1.3%. Additionally, the whole‐cell catalyst retained >52% enzyme activity after five repeated uses.CONCLUSIONThese results show that using ChCl/U to increase cell permeability improves the catalytic performance of the whole‐cell catalyst of E. coli BL21‐pET21a‐rhaB1. This approach has promising potential for the utilization of natural flavonoids. © 2019 Society of Chemical Industry

Caffeic acid (CA) as a strong antioxidant has lower solubility in nonpolar media, which limits its application in the food industry. To increase the lipophilicity of CA, 1-caffeoylglycerol (1-CG) was synthesized by lipasecatalyzed transesterification of alkyl caffeates in solvent-free system and its antioxidant capacity was investigated. Methyl caffeate was screened as the appropriate substrate from tested alkyl caffeates with a yield of 90.63%. Ethyl acetate was used for extracting 1-CG from enzymatic reactants and could be easily recycled. The produced 1-CG had 2.5-and 10-fold lower values of half maximal inhibitory concentration (IC 50 ) (10.86 and 3.99 μM) than butylated hydroxyanisole by 1,1-diphenyl-2-picrylhydrazyl radical scavenging and β-carotene-linoleic acid assays, respectively. Thus, 1-CG is an excellent antioxidant for application in the functional food industry. Using alkyl caffeates and glycerol as substrates to produce 1-CG catalyzed by immobilized lipase in a solvent-free system is a simple, selective, and safe bioprocess that can readily be achieved in the food industry, and the product 1-CG could be widely applied in food, nutraceutical, and biotechnological products.

BACKGROUND: Enzymatic catalysis in a microchannel under continuous flow has attracted increasing scientific interest. It allows for surfaces with higher specificities for heat and mass transfer and makes it easier to control reaction parameters. However, its applications are limited by a lesser amount of loading and cycle of use of the immobilized enzyme. A series of groove-typed channel microreactors with surface geometry patterns were first established for effective immobilization of naringinase, which was used to produce isoquercitrin from rutin via hydrolysis. RESULTS:Of the tested groove-typed channel microreactors with surface geometry patterns, the enzyme adsorbing capacities of all were increased compared to that with smooth surface. The enzyme adsorbing capacity increased 1.32-fold in the grooved microreactor with triangular pattern. Excellent yields of isoquercitrin production were produced in grooved channel immobilized enzyme microreactors with triangular surfaces. A yield of 91.72 ± 0.65% was obtained in 10 min, the microreactor could be reused 12 times with a residual activity over 56%. Efficient transfer of heat and mass were attained in the grooved microreactors with surface geometry patterns. The Poiseuille number and Nusselt number were increased by 20.61% and 29.63%, respectively, using fluid mechanics analysis in the grooved microreactor with triangular pattern. CONCLUSION: The grooved microreactor with geometry pattern surface provided an efficient method for the high production of isoquercitrin, which is promising for enzyme immobilization and catalysis.

Glycoamino acids and glycoproteins, especially C-glycoamino acids and C-glycoproteins, attract tremendous interests in the realm of biology and chemistry due to their wide occurrence in natural products, excellent pharmacodynamic properties and dynamic stability. Compared with the traditional construction of the amino acid or the glycosyl moiety de novo, postmodification of amino acids and peptides through direct glycosylation reactions constitute a powerful synthetic approach to attaining C-glycoamino acids and C-glycopeptides rapidly on account of the high step-economy, broad functional group tolerance, and conservation of the chirality of the amino acid and glycosyl moieties. In this review, the recent developments in the synthesis of C-glycoamino acids and C-glycopeptides via the post-modification of amino acids and peptides are summarized. Additionally, the important and representative examples, synthetic applications, and crucial mechanism investigations of these glycosylation reactions are also highlighted.