Physical immobilization of laccase on an electrode by means of poly(ethyleneimine) microcapsules

Microcapsules of poly(ethyleneimine) were used to immobilize laccase on the surface of an electrode and its mediated electron transfer was studied with the redox mediator p-phenylenediamine (PPD). The microcapsules consisted of a cross-linked PEI wall generated from an emulsion of an aqueous phase containing the enzyme. The reaction of encapsulated laccase with PPD was studied by spectrophotometry and oxygen consumption. We found that the encapsulation resulted in a small shift for the optimum pH and a lower K_m value when compared to free laccase. These differences are attributed to the charged micro-environment offered by the microcapsules. The microcapsules were then deposited on a glassy carbon electrode and chronoamperometry was used to evaluate the mediated electron transfer between the enzyme and the electrode. No significant differences in term of optimum pH and K_m occurred upon capsules deposition on the electrode. The response time of the electrode for PPD oxidation was higher than those found in the literature, which suggests that the PEI capsule wall offers some resistance to mediator permeation, an hypothesis that was verified by RDE measurements. The charged nature of the PEI membrane appeared to affect several parameters of the laccase-mediator reaction and the effect of pH and mediator charge on this reaction are reported. The immobilization platform under study can be applied to different enzyme-mediator systems than the laccase-PPD used here and is relevant to the development of bioelectrocatalytic systems.     

A Comparative Study between Conventional and Advanced Extraction Techniques: Pharmaceutical and Cosmetic Properties of Plant Extracts

This study aimed to compare the influence of extraction methods on the pharmaceutical and cosmetic properties of medicinal and aromatic plants (MAPs). For this purpose, the dried plant materials were extracted using advanced (microwave (MAE), ultrasonic (UAE), and homogenizer (HAE) assisted extractions) and conventional techniques (maceration, percolation, decoction, infusion, and Soxhlet). The tyrosinase, elastase, α-amylase, butyryl, and acetylcholinesterase inhibition were tested by using L-3,4 dihydroxy-phenylalanine, N-Succinyl-Ala-Ala-p-nitroanilide, butyryl, and acetylcholine as respective substrates. Antioxidant activities were studied by ABTS, DPPH, and FRAP. In terms of extraction yield, advanced extraction techniques showed the highest values (MAE > UAE > HAE). Chemical profiles were dependent on the phenolic compounds tested, whereas the antioxidant activities were always higher, mainly in infusion and decoction as a conventional technique. In relation to the pharmaceutical and cosmetic properties, the highest inhibitory activities against α-amylase and acetylcholinesterase were observed for Soxhlet and macerated extracts, whereas the highest activity against tyrosinase was obtained with MAE > maceration > Soxhlet. Elastase and butyrylcholinesterase inhibitory activities were in the order of Soxhlet > maceration > percolation, with no activities recorded for the other tested methods. In conclusion, advanced methods afford an extract with high yield, while conventional methods might be an adequate approach for minimal changes in the biological properties of the extract.