Fast and Simple UPLC-Q-TOF MS Method for Determination of Bitter Flavan-3-ols and Oligomeric Proanthocyanidins: Impact of Vegetable Protein Fining Agents on Red Wine Composition.

Wine phenolic compounds, particularly proanthocyanidins (PAs), play a significant role in wine sensory characteristics, specifically bitterness and astringency. Although not consensual, flavan-3-ols and oligomeric PAs are generally considered the primary contributors to wine bitterness. Patatin, a vegetable protein fining agent, has been explored as an alternative to animal and synthetic fining agents for reducing wine bitterness. However, contradictory results exist regarding its effectiveness in removing flavan-3-ols and oligomeric PAs in red wines. In this work, a UPLC-Q-TOF MS/MS method was optimized and validated for accurately measuring flavan-3-ols, as well as dimeric and trimeric PAs, in red wines. The MS/MS analysis of flavan-3-ols, in addition to the typical fragmentation described in the literature, revealed an intense mass fragment resulting from the loss of C3O2 and C3O2 + H2O from the parent ion. It was observed that flavan-3-ols and PAs undergo oxidation during sample preparation, which was reversed by the addition of 5 g/L of ascorbic acid. The method demonstrated good linearity range (2 mg/L to 20 mg/L), detection limit (0.3 mg/L to 0.7 mg/L), quantification limit (0.8 mg/L to 2.2 mg/L), precision (repeatability 2.2% to 7.3%), and accuracy (recovery 98.5% to 100.5%). The application of patatin at different doses (5 g/L to 30 g/L) in two different red wine matrices did not reduce the levels of monomeric, dimeric, and trimeric PAs in red wines. However, similar behaviors were observed for pea protein and gelatin. Therefore, wine fining trials and efficiency measurements of the treatments in each matrix are strongly advised.

Discrimination of Port wines by style and age using chromatic characteristics, phenolic, and pigment composition.

The colour of the different Port wine styles and indication of age (IOA) categories is a distinctive quality parameter influenced by the grapes and ageing process. The impact of Port wine styles and IOA on phenolic composition is mostly unknown. This work aims to study the chromatic characteristics (CIELab) and their relation with the phenolic composition of White, Tawny, and Ruby Port wines and evaluate the feasibility of its utilisation for their discrimination. Port wine styles and IOA categories can be discriminated by their chromatic characteristics, using different data analysis models. The higher b* values, corresponding to the brownish/yellowish colour of Tawny and White Ports belonging to higher IOA categories, seem more related to the sugar browning than the oxidative change in phenolic compounds. However, this last process is essential for the red colour (a*) decrease of Tawny Port wines with higher IOA.

Development and validation of a multiple headspace solid-phase microextraction method for accurate and precise analysis of the aroma of Tawny and White Port wines.

An accurate and precise Multiple Headspace Solid-Phase Microextraction (MHS-SPME) method was developed and validated for quantifying the volatile composition of White and Tawny Port wines. SPME extraction conditions were optimised using a four-factor three-level Box-Behnken design with three blocks and two replications. Optimal extraction conditions were similar for both Port wines. The method showed good linearity (0.001-50 mg/L), precision (<5%), and detection limits (<1µg/L), well below the olfactory detection threshold. Recoveries higher than 95 % were obtained. Twenty-three aroma compounds were quantified in Tawny and, for the first time, in White Port wines, including five acids, fourteen esters, the most abundant class, and four norisoprenoids, whose levels apparently increased with age. White Port wines had a lower abundance of aroma compounds. Results show that this MHS-SPME method is suitable for analysing volatile composition of White and Tawny Port wines, with reduced costs, manipulation time and eliminating matrix effects.

Reductive amination of aldehyde 2,4-dinitrophenylhydrazones using cyanoborohydride for determination of selected carbonyl compounds in Port wines, table wines, and wine spirits.

Carbonyl compounds are mainly analysed by HPLC with ultraviolet detection after reaction with DNPH, yielding carbonyl-hydrazones. The presence of geometrical isomers whose relative abundance is dependent on the reaction condition introduces analytical errors and increases the complexity of the chromatograms. In this work, a simple, fast, and robust method for determining pyruvic acid, acetaldehyde, and α-ketobutyric acid in Port wines, dry table wines, and wine spirits by reductive amination of aldehyde 2,4-dinitrophenylhydrazones using cyanoborohydride followed by HPLC-DAD was developed, optimised and validated. The developed method was simple and showed good performance in several parameters such as linearity (0.025-200 mg/L), detection limits (0.0043-0.0097 mg/L), quantification (0.014-0.032 mg/L), precision (1.1-4.2 %) and accuracy (99.02 %). The method was applied to five different wine matrices, White, Tawny, and Ruby Port wines, white and red table wines, and wine spirits. The quantification of these carbonyl compounds simultaneously was achieved in Port wines for the first time.

Efficiency of carboxymethylcellulose in red wine tartaric stability: Effect on wine phenolic composition, chromatic characteristics and colouring matter stability.

In this work, the effect of carboxymethylcellulose structural features on the efficiency to prevent potassium hydrogen tartrate precipitation in red wines and on the phenolic composition, chromatic characteristics and colouring matter stability was studied. The degree of substitution of carboxymethylcellulose was important for its efficiency in highly unstable wines. Application of carboxymethylcellulose doesn't result in a significant change in the phenolic, monomeric anthocyanin composition, colour intensity, and chromatic characteristics of red wines. Sensory analysis also showed that carboxymethylcellulose doesn't have a significant impact on wine sensory attributes. Carboxymethylcellulose doesn't decrease the colouring matter stability. The use of turbidity for evaluating the colouring matter stability of wines has severe drawbacks as the turbidity value measured might not be related to the amount of suspended material. Therefore, the application of carboxymethylcellulose in red wines is efficient in increasing tartaric stability without impacting on the phenolic composition, sensory characteristics, and colouring matter stability.

An accurate single-step LLE method using keeper solvent for quantification of trace amounts of sotolon in Port and white table wines by HPLC-DAD.

Sotolon has been reported to play an important role in the typical aroma of aged Port wines. A simple and cheap single-step liquid-liquid extraction (LLE) using glycerol as a keeper for liquid chromatography/ultra-violet absorption quantification of sotolon in Port wines is proposed in this work. The glycerol plays a protective role during the concentration of the extracts increasing the sotolon recovery as well the method repeatability. The proposed method yields chromatograms without interfering compounds and a forty-fold enrichment of sotolon. The detection and quantification limits were far below the sotolon odour threshold in Port wine (19 µg/L). The method was also validated for dry white table wines with good validation parameters. The methodology was successfully applied to selected commercial Tawny, Ruby, and White Port wines, being reported the presence of sotolon in young Ruby and White Port wines for the first time, although below the olfactory detection threshold.

4-Ethylphenol, 4-ethylguaiacol and 4-ethylcatechol in red wines: Microbial formation, prevention, remediation and overview of analytical approaches.

The presence of 4-ethylphenol, 4-ethylguaiacol and 4-ethylcatechol in red wines affect negatively their aroma conferring horsy, barnyard, smoky and medicinal aromatic notes. These volatile phenols formed from free hydroxycinnamic acids and their ethyl esters by Dekkera/Brettanomyces yeasts, can contaminate wines. Their formation can cause serious negative economic impact to the wine industry worldwide as consumers tend to reject these wines. For these reasons various preventive and remedial treatments have been studied. This review summarises the wine microbial volatile phenols formation, preventive measures during winemaking and remedial treatments in finished wines along with their advantages and limitations for dealing with this sensory defect and impact on wine quality. Also it is important to control the levels of volatile phenols in wines using fast and convenient analytical methods namely with a detection limit below their olfactory perception threshold. The analytical methods available for quality control and performance characteristics as well their advantages and disadvantages when dealing with a complex matrix like wine are discussed in detail.

A simple dispersive solid phase extraction clean-up/concentration method for selective and sensitive quantification of biogenic amines in wines using benzoyl chloride derivatisation.

A simple, quick, cheap and green dispersive solid phase extraction (dSPE) method followed by benzoyl chloride pre-column derivatisation for HPLC-UV determination of twelve biogenic amines (BAs) in wines is proposed for the first time. The dSPE using a strong cation exchange resin increased the selectivity and sensitivity of the analysis by elimination of interfering compounds and a five-fold enrichment of BAs. The method presented an adequate precision and linearity with detection limits ranging from 0.133 to 0.509 mg/L. Recoveries ranging from 72 to 99% prove the accuracy of the method for determining BAs in red, white and Tawny Port wine samples yielding chromatograms clean from interferents. The method was applied successfully to the analysis of 31 young red wines from different Portuguese wine regions. The dSPE method although has a potential of broader application to other food matrixes, other derivatisation procedures than benzoyl chloride and other detectors.

Reduction of 4-ethylphenol and 4-ethylguaiacol in red wine by activated carbons with different physicochemical characteristics: Impact on wine quality.

Activated carbon (AC) could be a solution to remove 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) off-flavours from Dekkera/Brettanomyces contaminated red wines. The relation between AC physicochemical characteristics and removal efficiency of these compounds is unknown. The impact of ACs characteristics on 4-EP and 4-EG removal, phenolic and headspace aroma composition was studied. All ACs reduced significantly 4-EP and 4-EG levels (maximum 73%). Their efficiency was related to their surface area and micropores volume. A higher surface area of mesopores and total pore volume were detrimental for anthocyanins and colour intensity, while a higher surface area and micropores volume were important for removing phenolic acids. Volatile phenols reduction was more important for the positive fruity attribute perception than the abundance of headspace aroma compounds. With an optimal selection of the AC physicochemical characteristics it was possible to remove efficiently the volatile phenols without impacting negatively on the wine sensory quality.

Data on changes in red wine phenolic compounds, headspace aroma compounds and sensory profile after treatment of red wines with activated carbons with different physicochemical characteristics.

Data in this article presents the changes on phenolic compounds, headspace aroma composition and sensory profile of a red wine spiked with 4-ethylphenol and 4-ethylguaiacol and treated with seven activated carbons with different physicochemical characteristics, namely surface area, micropore volume and mesopore volume ("Reduction of 4-ethylphenol and 4-ethylguaiacol in red wine by activated carbons with different physicochemical characteristics: impact on wine quality" Filipe-Ribeiro et al. (2017) [1]). Data on the physicochemical characteristics of the activated carbons are shown. Statistical data on the sensory expert panel consistency by General Procrustes Analysis is shown. Statistical data is also shown, which correlates the changes in chemical composition of red wines with the physicochemical characteristics of activated carbons used.

A simple, cheap and reliable method for control of 4-ethylphenol and 4-ethylguaiacol in red wines. Screening of fining agents for reducing volatile phenols levels in red wines.

Brettanomyces/Dekkera produces 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) from hydroxycinnamic acids that affect the wine aroma and overall quality. A simple, cheap, fast and reliable quantitation method is needed for routine quality control of wines. In this work a simple method based on one simple liquid-liquid extraction with pentane/diethyl ether (2:1) and analysis by GC-MS allow to obtain very good recoveries (98-102%) and low quantification limits (24 and 11µg/L for 4-EP and 4-EG, respectively), well below the sensory threshold for these volatile phenols and with an adequate measurement uncertainty: 70, 1.75 and 78, 1.95 and 1.35µg/L for levels of 1000, 25µg/L for 4-EP and 1000, 25 and 10µg/L for 4-EG, respectively. In addition a screening of eight fining agents (mineral, protein and polysaccharide based) for reducing the levels of these volatile phenols in red wines was performed, and the impact on the physicochemical characteristics of red wines was evaluated. At the levels used, activated carbon was the most efficient fining agent in removing 4-ethylphenol and 4-ethylguaiacol from red wines (57%) resulting in a 75% decrease of headspace concentration of these volatile phenols. Lower reductions were observed when using egg albumin (19%) resulting in a 30% decrease in the headspace concentration. Other fining agents although not reducing the total amount of the volatile phenols present in wine decreased their concentrations in the headspace like isinglass (27%), carboxymethylcellulose (15%) and chitosan (27%). All of these fining agents could be a possibility for treating wine contaminated with 4-ethylphenol and 4-ethylguaiacol.