Fast Analysis of Caffeic Acid-Related Molecules in Instant Coffee by Reusable Sonogel-Carbon Electrodes.

Reusable Sonogel-Carbon electrodes containing carbon black (SNGC-CB) have been used for the electrochemical analysis of caffeic acid (CA) in real matrices. Measurements were firstly performed in standard solutions, in which SNGC-CB electrodes allowed the electrochemical determination of CA with high sensitivity and low limit of detection, equal to 0.76 µM. The presence of CB nanostructures in the formulation led to improved performances with respect to pristine SNGC electrodes. Then, measurements were performed in four instant coffees of different brands. A comparison between the results obtained by electrochemical, chromatographic and spectroscopic methods showed that SBGC-CB electrodes represent a simple and economic tool for the rapid assessment of caffeic acid-related molecules in instant coffees.

An electrochemical alternative for evaluating the antioxidant capacity in walnut kernel extracts.

A fast, precise and inexpensive alternative for evaluating the antioxidant activity (AA) in walnut kernel extracts is proposed. Traditional ABTS assay and an electrochemical index approach have been applied to evaluate the AA in walnuts. A fast and efficient defatting of the walnuts by ultrasound assisted extraction (UAE) was carried out. Later, for the extraction of polyphenolic compounds, a procedure based on UAE in ethanolic medium was used. The AA of the sample ethanolic extracts was expressed as both % of inhibition by the ABTS spectrophotometric method and the electrochemical index approach (EI) obtained by the ratio between current and potential peak values using differential pulse voltammetry (DPV) at a Sonogel-Carbon electrode. The behaviour of the EI approach have been explored using six polyphenols standards and walnut kernel extracts at pH 2. All the polyphenols appeared at an oxidation potential between 0.476 and 0.778 V. Eleven samples available to consumers were analysed. A high significant correlation (R2 = 0.927) between the spectrophotometric measurements and the EI approach of the walnut extracts was obtained.

A simple phosphorus determination in walnuts and assessment of the assimilable fraction.

In this work, a method for the determination of phosphorus in walnuts has been developed due to the fact that there is no specific method for this purpose. A closed-vessel microwave-assisted digestion of the samples was optimized and a modified molybdenum blue spectrophotometric method was carried out with excellent precision and selectivity. To differentiate assimilable and non-assimilable phosphorus, an easy extraction procedure using 1 M NH4Cl was used. FTIR spectra ensured that the phytate extraction was successful. A sampling of thirteen different walnuts available to consumers from different crops and geographical origin was performed. Comparative statistical tools to differentiate walnuts were also carried out. Significant differences based on total content of phosphorus were obtained. Finally, a correlation study between total phosphorus concentration and the non-assimilable fraction showed a non-linear relationship (R2 = 0.435). Therefore, in relation to consumer health the total phosphorus determination must be complemented with information about assimilable phosphorus.