Amperometric study of the inhibitory effect of carboxylic acids on tyrosinase

A sustainable amperometric biosensor for the analysis of ascorbic, benzoic, gallic and kojic acids through catechol detection. Innovation and signal processing

A sustainable catechol biosensor for the analysis of beverages and cosmetics.

An optical test strip for the detection of benzoic acid in food

Fabrication of a test strip for detection of benzoic acid was successfully implemented by immobilizing tyrosinase, phenol and 3-methyl-2-benzothiazolinone hydrazone (MBTH) onto filter paper using polystyrene as polymeric support. The sensing scheme was based on the decreasing intensity of the maroon colour of the test strip when introduced into benzoic acid solution. The test strip was characterized using optical fiber reflectance and has maximum reflectance at 375 nm. It has shown a highly reproducible measurement of benzoic acid with a calculated RSD of 0.47% (n = 10). The detection was optimized at pH 7. A linear response of the biosensor was obtained in 100 to 700 ppm of benzoic acid with a detection limit (LOD) of 73.6 ppm. At 1:1 ratio of benzoic acid to interfering substances, the main interfering substance is boric acid. The kinetic analyses show that, the inhibition of benzoic is competitive inhibitor and the inhibition constant (K_i) is 52.9 ppm. The activity of immobilized tyrosinase, phenol, and MBTH in the test strip was fairly sustained during 20 days when stored at 3 °C. The developed test strip was used for detection of benzoic acid in food samples and was observed to have comparable results to the HPLC method, hence the developed test strip can be used as an alternative to HPLC in detecting benzoic acid in food products.

Prediction of tyrosinase inhibition activity using atom-based bilinear indices

A set of novel atom-based molecular fingerprints is proposed based on a bilinear map similar to that defined in linear algebra. These molecular descriptors (MDs) are proposed as a new means of molecular parametrization easily calculated from 2D molecular information. The nonstochastic and stochastic molecular indices match molecular structure provided by molecular topology by using the kth nonstochastic and stochastic graph-theoretical electronic-density matrices, M(k) and S(k), respectively. Thus, the kth nonstochastic and stochastic bilinear indices are calculated using M(k) and S(k) as matrix operators of bilinear transformations. Chemical information is coded by using different pair combinations of atomic weightings (mass, polarizability, vdW volume, and electronegativity). The results of QSAR studies of tyrosinase inhibitors using the new MDs and linear discriminant analysis (LDA) demonstrate the ability of the bilinear indices in testing biological properties. A database of 246 structurally diverse tyrosinase inhibitors was assembled. An inactive set of 412 drugs with other clinical uses was used; both active and inactive sets were processed by hierarchical and partitional cluster analyses to design training and predicting sets. Twelve LDA-based QSAR models were obtained, the first six using the nonstochastic total and local bilinear indices and the last six with the stochastic MDs. The discriminant models were applied; globally good classifications of 99.58 and 89.96 % were observed for the best nonstochastic and stochastic bilinear indices models in the training set along with high Matthews correlation coefficients (C) of 0.99 and 0.79, respectively, in the learning set. External prediction sets used to validate the models obtained were correctly classified, with accuracies of 100 and 87.78 %, respectively, yielding C values of 1.00 and 0.73. This subset contains 180 active and inactive compounds not considered to fit the models. A simulated virtual screen demonstrated this approach in searching tyrosinase inhibitors from compounds never considered in either training or predicting series. These fitted models permitted the selection of new cycloartane compounds isolated from herbal plants as new tyrosinase inhibitors. A good correspondence between theoretical and experimental inhibitory effects on tyrosinase was observed; compound CA6 (IC(50)=1.32 microM) showed higher activity than the reference compounds kojic acid (IC(50)=16.67 microM) and L-mimosine (IC(50)=3.68 microM).

Preventing inhibition of tyrosinase with modified electrodes

Wines, especially red wines, contain numerous biologically active compounds, the most important of which are polyphenols, whose nutritional importance is attributed to their antioxidant power. Because of this, the detection of the amount of phenolic compounds in red wines becomes extremely important. However, using free enzyme in the determination of phenolic compounds in wines cannot reflect the actual values since there are also naturally found inhibitors in red wines. In this study, benzoic acid, cinnamic acid, and sorbic acid were utilized to understand the behavior of immobilized polyphenol oxidase in the conducting polymer matrices toward inhibition. Cinnamic acid was found to be the most powerful inhibitor for both free and immobilized enzyme in copolymer matrix of poly(terephthalic acid bis-(2-thiophen-3-yl-ethyl) ester) (PTATE) with polypyrrole (PPy). In the case of immobilized enzyme in PPy matrix, it was observed that sorbic acid is a stronger inhibitor than cinnamic acid. The inhibitory effects of these inhibitors on PPO were compared with respect to both the structural differences of inhibitors and conducting polymer matrices.

Phenols monitoring and Hill coefficient evaluation using tyrosinase-based amperometric biosensors

Sensitive amperometric biosensors for phenols compounds, based on tyrosinase (polyphenoloxidase, PPO) immobilized on a Pt electrode in an electropolymerized poly-amphiphilic pyrrole matrix or cross-linked with glutaraldehyde, were constructed and compared. Steady-state amperometric measurements, performed at -50 mV vs. SCE in aqueous phosphate buffer containing LiClO(4) 0.1 M (pH 7) as well as in a chloroform solution containing 0.1 M C(6)H(5)CH(2)N(CH(3))(3)Cl, were used in order to compare the electroanalytical and kinetic parameters of the investigated amperometric biosensors in aqueous and nonaqueous media. It was established that the polypyrrole matrix has a higher efficiency for enzyme retention resulting in higher bioelectrode sensitivity, both in aqueous buffer (690 microA M(-1)) and in chloroform (149 microA M(-1)).