Analytical innovations in the detection of phenolics in wines

Assessment of the Polyphenol Indices and Antioxidant Capacity for Beers and Wines Using a Tyrosinase-Based Biosensor Prepared by Sinusoidal Current Method

The application of a novel Poly(3,4-ethylenedioxythiophene)-Tyrosinase/Sonogel-Carbon electrode (PEDOT-Tyr/SNGC) biosensor to beers and wines analysis is proposed. This biosensor implies a new Sinusoidal Current (SC) electrodeposition method to immobilize the enzyme generating a nanostructure surface. The biosensors were characterized electrochemically, employing cyclic voltammetry and electrochemical impedance spectroscopy. Sensitivity, limit of detection, and correlation coefficients of the linear fitting were 2.40 × 10^-4 µA·µM^-1, 4.33 µM, and R² = 0.9987, respectively. Caffeic acid is used as the reference polyphenol. A sampling of nine beers (four lager, three stout, and two non-alcoholic beers), and four wines (three red and one white wine) purchased in a local store was performed. The Polyphenol indeces for beers and wines have been assessed using the proposed biosensor, and the obtained values are in agreement with the literature data. Antioxidant properties of the samples using the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical spectrophotometric method were also evaluated. The correlation between the polyphenol index and the antioxidant capacity was obtained for beers and wines.

Luminescent determination of flavonoids in orange juices by LC with post-column derivatization with aluminum and terbium

A new post-column derivatization system is described and applied to the determination of flavonoids in citric beverages after their separation by LC using a monolithic column. The derivatization involves the formation of the chelates of the analytes with aluminum (III) and terbium (III) in the presence of the surfactant SDS and the measurement of the terbium sensitized luminescence at lambda(ex) 360 and lambda(em) 545 nm. Naringin, hesperidin, quercetin, naringenin, and kaempferol have been chosen as analyte models. The large Stokes shift and the relatively long wavelength emission of terbium(III) can minimize interferences from background sample matrix, which usually emit at shorter wavelengths. Calibration graphs were constructed in the intervals 6.0-1700 ng/mL naringin, 9.8-1700 ng/mL hesperidin, 2.1-2000 ng/mL quercetin, 5.2-1500 ng/mL naringenin and 2.5-2000 ng/mL kaempferol, with regression coefficients higher than 0.9935 in all instances. The precision of the method, expressed as RSD%, was established at two concentration levels, with values of 1.3 and 4.7%, which corresponded to the minimal and maximal error zones of the calibration graphs. The practical usefulness of the method is demonstrated by the analysis of orange juices, which were diluted and directly injected into the chromatographic system, obtaining recoveries between 86.9 and 108.2%.

Optimization of a solid-phase extraction method using copolymer sorbents for isolation of phenolic compounds in red wines and quantification by HPLC

Different solid-phase extraction (SPE) cartridges for the isolation of most of the phenolic compounds present in wines in low concentration were assayed and compared with the C18 SPE sorbent, which is the most common sorbent used for the isolation of these compounds. The use of C18 cartridges has several disadvantages; therefore, a SPE method using copolymer cartridges was developed, optimized, and validated. The method proposed seems to be a good alternative to replace C18 cartridges for the isolation of wine phenolic compounds. The advantages of the proposed SPE method with the HLB cartridge are that interferences can be eliminated with water without losing the compounds of great interest; the method has very good repeatability, reproducibility, and high percentages of recovery; it has a higher sensitivity and loading capacity than silica-based C18 cartridges due to the larger surface area of this type of sorbent, and the method is not adversely affected by drying, being more reproducible than C18 cartridge.

Rapid-resolution liquid chromatography/mass spectrometry for determination and quantitation of polyphenols in grape berries

A rapid-resolution liquid chromatography/mass spectrometric (RRLC/MS) method for detection and quantitation of polyphenols in grape berry skins and seeds has been developed. Pulp-free berry skins were treated with liquid nitrogen and ground; seeds were also ground. Then, 3 g of samples were extracted with 30 mL of a mixture of methanol/water/formic acid 70:30:1 (v/v/v) under sonication and 1 microL of the final extract was injected into two 100 x 2.1 mm i.d., 1.8 microm Zorbax Eclipse plus C18 columns connected in series. Compounds were fractionated using a gradient elution of acidified acetonitrile/methanol 50:50 (v/v)/water. Columns were thermostatted at 70 degrees C. MS was carried out on an Agilent 6410 QqQ instrument equipped with an electrospray ionization source. Positive and negative MS/MS product ion scans were used for compound identification, whereas positive full scan MS in the m/z range 200-1400 was used for quantitation. By means of mass spectra comparison, various flavonols, flavan-3-ols, anthocyanins and stilbenes were identified. Quantitation was performed by external calibration, and concentration values were corrected for matrix effect that was evaluated in separate experiments. Semi-quantitative estimation was performed for compounds for which standards were not commercially available. Recoveries ranged from 90-102% with relative standard deviation (RSD) <5%, whereas the between samples RSD was in the range 4-12%. Two surrogate standards were used for quality control. The developed method was applied to analyze the polyphenol content of three Vitis vinifera table cultivars at physiological maturity and after proper preservation for 6 weeks. Results demonstrated that during preservation about half of the polyphenol content was lost.