Fructose determination in fruit juices using an electrosynthesized molecularly imprinted polymer on reduced graphene oxide modified electrode.

The present work reports the development of a novel electrochemical sensor for the selective detection of fructose. The sensor was developed through electropolymerization of a molecularly imprinted polymer film on a reduced graphene oxide modified electrode. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, atomic force microscopy and RAMAN spectroscopy. Through the application of the modified electrode, the recognition of fructose molecules occurred in a concentration range of 1.0 × 10-14 to 1.0 × 10-11 mol L-1, under a Langmuir adsorption isothermal model. The sensitivity and limits of detection and quantification obtained for the sensor were 9.9 × 107 A L mol-1, 3.2 × 10-15 mol L-1 and 1.1 × 10-14 mol L-1, respectively. The analytical method used for the detection of fructose presented good reproducibility, stability and accuracy, and was successfully applied for the quantification of this sugar in orange, apple and grape juices.

Prediction of beef color using time-domain nuclear magnetic resonance (TD-NMR) relaxometry data and multivariate analyses.

Time-domain nuclear magnetic resonance and chemometrics were used to predict color parameters, such as lightness (L*), redness (a*), and yellowness (b*) of beef (Longissimus dorsi muscle) samples. Analyzing the relaxation decays with multivariate models performed with partial least-squares regression, color quality parameters were predicted. The partial least-squares models showed low errors independent of the sample size, indicating the potentiality of the method. Minced procedure and weighing were not necessary to improve the predictive performance of the models. The reduction of transverse relaxation time (T2 ) measured by Carr-Purcell-Meiboom-Gill pulse sequence in darker beef in comparison with lighter ones can be explained by the lower relaxivity Fe2+ present in deoxymyoglobin and oxymyoglobin (red beef) to the higher relaxivity of Fe3+ present in metmyoglobin (brown beef). These results point that time-domain nuclear magnetic resonance spectroscopy can become a useful tool for quality assessment of beef cattle on bulk of the sample and through-packages, because this technique is also widely applied to measure sensorial parameters, such as flavor, juiciness and tenderness, and physicochemical parameters, cooking loss, fat and moisture content, and instrumental tenderness using Warner Bratzler shear force. Copyright © 2016 John Wiley & Sons, Ltd.