-The enzimatic activity of peroxidase (POD) and polyphenoloxidase (PPO) extracted from three grape cultivars (Vitis vinifera L.), cultivated in Marialva city, state of Paraná, was evaluated in this study. The enzymatic extracts were prepared starting from the Rubi, Borbon and Benitaka grape cultivars pulp and peel. The activity of the peroxidase was 53.00 units/100 g in the extract from the Rubi cultivar peel, and 327.00 units/100 g from the Benitaka cultivar, these values being superior to those observed in the same cultivars pulp extracts, which were 7.67 units/100 g and 44.00 units/100 g respectively. However, the result was opposite in the Borbon cultivar, with values of 141.11 units/100 g in the pulp and 11.50 units/100 g in the peel being found. The results of the polyphenoloxidase in the Borbon cultivar activity were 100.18 units/100 g in the pulp and 102.60 units/100 g in the peel, and in the Rubi and Benitaka cultivars were 60.40 units/100 g, 48.62 units/100 g in the pulp and 17.40 units/100 g, and 26.20 units/100 g in the peel, respectively. Protein determination was carried out in each extract, and the results found in the pulp and peel, respectively, were 0.56 and 0.64 mg/100 g for cultivar Benitaka, 1.38 and 6.45 mg/100 g for cultivar Rubi, and 21.38 and 5.68 mg/100 g for Borbon. The extracts were submitted to thermal treatments (60°C, 65°C, 70°C and 75°C for a 1 to 10 minutes period) to observe the behavior of the peroxidase and polyphenoloxidase enzymatic activity, being verified a continuous decrease of the peroxidase and polyphenoloxidase activities as a result of the thermal treatment. The extracts of the Rubi and Benitaka cultivars were more heat stable than the extract from the Borbon cultivar for both enzymes. However, the temperatures used were not enough for a total inactivation of the enzymes.

No abstract

A sensitive and simple electrochemical method for norepinephrine (NE) determination was developed based on a poly(1,5-diaminonaphthalene) film electrode (PDAN). Cathodically pretreated PDAN presents good selectivity, sensitivity, and reproducibility for NE. The polymer film can be easily electropolymerized onto a platinum electrode by cyclic voltammetry in 1.0 M HClO 4 . A cathodic pretreatment, consisting of the application of a potential of À0.7 V for 3 s (vs. Ag/AgCl) to PDAN before each voltammetric measurement, enhanced the electrochemical activity of NE with no inference of ascorbic acid (AA). In optimized conditions, PDAN presents linear responses for NE in the range of 9.90 to 90.9 mM by differential pulse voltammetry (DPV) with a detection limit of 1.82 mM. A relative standard deviation of 3.0 % was obtained for 10 consecutive measurements of 40.0 mM NE solutions. The cathodically pretreated PDAN was successfully applied for NE determination in pharmaceutical formulation samples.

A simple and sensitive method for simultaneously measuring dopamine (DA), ascorbic acid (AA), and uric acid (UA) using a poly(1-aminoanthracene) and carbon nanotubes nanocomposite electrode is presented. The experimental parameters for composite film synthesis as well as the variables related to simultaneous determination of DA, AA, and UA were optimized at the same time using fractional factorial and Doehlert designs. The use of carbon nanotubes and poly(1-aminoanthracene) in association with a cathodic pretreatment led to three well-defined oxidation peaks at potentials around À0.039, 0.180 and 0.351 V (vs. Ag/AgCl) for AA, DA, and UA, respectively. Using differential pulse voltammetry, calibration curves for AA, DA, and UA were obtained over the range of 0.16-3.12 10 À3 mol L , respectively. The proposed method was successfully applied to determine DA, AA, and UA in biological samples with good results.