Determination of kinetic parameters of the enzymatic reaction between soybean peroxidase and natural antioxidants using chemometric tools

The oxidation of eugenol, isoeugenol and vanillin natural antioxidants catalyzed by the soybean peroxidase enzyme was studied using uv-vis spectroscopy. An experimental design was used to optimize the different variables. The multivariate curve resolution method was used to obtain the profiles of antioxidant absorbance's as a function of time due to uv-vis absorption bands of both antioxidants and the enzymatic reaction product/s show a strong overlap. From these results, apparent Michaelis-Menten constants as well as the kinetic parameters k1 and k3 involved in the catalytic cycle of peroxidases were calculated. The antioxidant apparent acidity constants were also determined at different pH's from uv-vis spectrophotometric measurements. Values of k1 were (0.6 ± 0.1) × 105 M-1 s-1, (2.0 ± 0.2) × 105 M-1 s-1 and (7.0 ± 0.5) × 106 M-1 s-1 and k3 (4.0 ± 0.2) × 105 M-1 s-1, (6.0 ± 0.6) × 105 M-1 s-1 and (6.0 ± 0.9) × 106 M-1 s-1 for eugenol, isoeugenol and vanillin, respectively.

Development and validation of a LC-MS/MS method for the determination of isoeugenol in finfish

A simple, rapid, selective and sensitive LC-MS/MS method was developed and validated for the determination of isoeugenol in finfish using an off-line dansylation derivatization step to enhance signal intensity. The sample was extracted with 10mL acetone using a tissue homogenizer, followed by derivatization with dansyl chloride and analysis by liquid chromatography tandem mass spectrometry. The method detection limit ranged from 0.2 to 0.7ngg^-1 in six fish species. The limit of quantification was 2.5ngg^-1 in each species. Recoveries of isoeugenol at three different levels (5, 10 and 20ngg^-1) over two different days ranged from 91.2% to 108.0%. Precision (%RSD_R) values determined at 10ngg^-1 were 4.3%, 8.0%, 5.3%, 5.1%, 2.6% and 8.0% for tilapia, catfish, trout, salmon, hybrid striped bass and yellow perch, respectively. Studies of linearity in the range 2.5-40ngg^-1 produced determination coefficients (R²) above 0.997 for all matrices.