Moving and unsinkable graphene sheets immobilized enzyme for microfluidic biocatalysis.

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.

Nano-polyplex based on oleoyl-carboxymethy-chitosan (OCMCS) and hyaluronic acid for oral gene vaccine delivery.

Here we described nano-polyplexes (NPs) made of oleoyl-carboxymethy-chitosan (OCMCS)/hyaluronic acid (HA) as novel potential carriers for oral gene vaccines delivery. Aerolysin gene (aerA) of Aeromonas hydrophila as microbial antigen was efficiently loaded to form OCMCS-HA/aerA (OHA) NPs. OHA NPs performed the optimal parameters, i.e. smallest (154.5±9.4nm), positive charged (+7.9±0.5mV) and monodispersed system with the N/P ratio of 5 and OCMCS/HA weight ratio of 4. Upon the introduction of HA, OHA NPs was beneficial for the DNA release in intestinal environments in comparison to OA NPs. The mean fluorescence intensity detected in Caco-2 cells incubated with OHA NPs was about 2.5-fold higher than that of OA NPs; however, it decreased significantly in the presence of excess free HA. The OHA NPs and OA NPs decreased the transepithelial electric resistance (TEER) of Caco-2 monolayers obviously and induced increasing the apparent permeability coefficient (Papp) of DNA by 5.45-6.09 folds compared with free DNA. Significantly higher (P<0.05) antigen-specific antibodies were detected in serum after orally immunized with OHA NPs than that immunized with OA NPs and DNA alone in carps. These results enable the OHA NPs might resolve challenges arising from gastrointestinal damage to gene antigens, and offer an approach applicable for oral vaccination.

Alkyl caffeates improve the antioxidant activity, antitumor property and oxidation stability of edible oil.

Caffeic acid (CA) is distributed widely in nature and possesses strong antioxidant activity. However, CA has lower solubility in non-polar media, which limits its application in fat-soluble food. To increase the lipophilicity of natural antioxidant CA, a series of alkyl caffeates were synthesized and their antioxidant and antitumor activities were investigated. The antioxidant parameters, including the induction period, acid value and unsaturated fatty acid content, of the alkyl caffeates in edible oil were firstly investigated. The results indicated that alkyl caffeates had a lower DPPH IC50 (14-23 µM) compared to CA, dibutyl hydroxy toluene (BHT) and Vitamin C (24-51 µM), and significantly inhibited four human cancer cells (SW620, SW480, SGC7901 and HepG2) with inhibition ratio of 71.4-78.0% by a MTT assay. With regard to the induction period and acid value assays, methyl and butyl caffeates had higher abilities than BHT to restrain the oxidation process and improve the stability of edible oil. The addition of ethyl caffeate to oil allowed maintenance of a higher unsaturated fatty acid methyl ester content (68.53%) at high temperatures. Overall, the alkyl caffeats with short chain length (n<5) assessed better oxidative stability than those with long chain length. To date, this is the first report to the correlations among the antioxidant activity, anticancer activity and oxidative stability of alkyl caffeates.

A novel chemoenzymatic synthesis of propyl caffeate using lipase-catalyzed transesterification in ionic liquid.

Propyl caffeate has the highest antioxidant capacity in the caffeate alkyl esters family, but industrial production of propyl caffeate is hindered by low yields using either the chemical or enzymatic catalysis method. To set up a high-yield process for obtaining propyl caffeate, a novel chemoenzymatic synthesis method using lipase-catalyzed transesterification of an intermediate methyl caffeate or ethyl caffeate and 1-propanol in ionic liquid was established. The maximum propyl caffeate yield of 98.5% was obtained using lipase-catalyzed transesterification under the following optimal conditions: Novozym 435 as a biocatalyst, [Bmim][CF3SO3] as a medium, a molar ratio of methyl caffeate to 1-propanol of 1:5, a mass ratio of methyl caffeate to lipase of 1:20, and a reaction temperature of 60°C. The two-step conversion of caffeic acid to propyl caffeate via methyl caffeate is an efficient way to prepare propyl caffeate with an overall yield of 82.7%.