A preliminary study of non-coloured phenolics in wines of varietal white grapes (códega, gouveio and malvasia fina): effects of grape variety, grape maturation and technology of winemaking

White wine phenolics: current methods of analysis

White wine phenolic analyses are less common in the literature than analyses of red wine phenolics. Analytical techniques for white wine phenolic analyses using spectrophotometric, chromatographic, spectroscopic, and electrochemical methods are reported. The interest of research in this area combined with the advances in technology aimed at the winemaking industry are promoting the establishment of novel approaches for identifying, quantifying, and classifying phenolic compounds in white wine. This review article provides an overview of the current research into white wine phenolics through a critical discussion of the analytical methods employed. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Chemical and sensory characterisation of sweet wines obtained by different techniques

Little is known about the chemical and sensory characteristics of natural sweet wines obtained by different grape dehydration processes. The main aim of this work is to characterise several natural sweet wines, in order to understand the influence of grape dehydration on the chemical and sensory profile of those wines. First, conventional oenological parameters and low molecular weight phenolic compounds have been determined. Next, sensory descriptive analysis was performed on individual samples based on citation frequencies for aroma attributes and conventional intensity scores for taste and mouth-feel properties. Low molecular weight phenolic compounds and acidity were found in a lower concentration in most wines from off-vine dried grapes. Late harvest wine presented higher amounts of phenolics. White wines showed higher sensory and chemical acidity. Most wines obtained from off-vine and on-vine grape dehydration presented common notes of dry fruits and raisins as aroma properties. Chemical and sensory analyses performed in this study were able to define sweet wines. No significant differences have been found in chemical and sensory profiles of sweet wines according to dehydration processes of the grapes. Late harvest wine and white wines were differentiated from other wines through chemical and sensory analysis.

Physicochemical and Sensory Characterization of Malvasia Wines from Different Mediterranean Areas

The identity of different Mediterranean Malvasia wines from Lipari (Aeolian Islands), Sardinia, Crete, and the Canaries by correlating sensory attributes with physicochemical parameters was determined. The Malvasia wines from Lipari had a wide and harmonic aromatic profile with floral, fruity, and exotic fruit aromas in addition to honey, fruit, and raisin flavors. The similarity of sensory characteristics between the Lipari and Crete samples may have originated from the geographic proximity and from the frequent cultural exchanges between Southern Italy and Greece. The Sardinian Malvasia wines had their own identity based on the prevailing citrus aroma, wood aroma and flavor, high alcohol content, and distinctive color parameters. The Canary Malvasia wine was characterized by high clearness and acidity without particular aromatic attributes.

Profiles of Phenolic Acids and Flavan-3-ols for Select Chinese Red Wines: A Comparison and Differentiation According to Geographic Origin and Grape Variety

The profiles of phenolic acids and flavan-3-ols for the selected Chinese red wines and the potential of using phenolic acids and flavan-3-ols to differentiate the geographic origin and grape variety of wines from China are investigated in this study. Significant differences and markers could be found according to the geographical origin and grape variety. Through a canonical discriminant analysis a good differentiation was developed according to the geographic origin or grape variety, and the accuracy of the discriminant model was 88.9% and 100%, respectively. According to the phenolic acid and flavan-3-ols profiles of the wine samples and good differentiation in the region and the variety discriminant analysis, minimal fraudulent claims were noted for the Chinese red wines investigated.

PRACTICAL APPLICATION

This study provides some help for the protection of geographical origin and monovarietal wine claims.

Statistical analysis of wines using a robust compositional biplot

Eight phenolic acids (vanillic, gentisic, protocatechuic, syringic, gallic, coumaric, ferulic and caffeic) were quantitatively determined in 30 commercially available wines from South Moravia by gas chromatography-mass spectrometry. Raw (untransformed) and centered log-ratio transformed data were evaluated by classical and robust version of principal component analysis (PCA). A robust compositional biplot of the centered log-ratio transformed data gives the best resolution of particular categories of wines. Vanillic, syringic and gallic acids were identified as presumed markers occurring in relatively higher concentrations in red wines. Gentisic and caffeic acid were tentatively suggested as prospective technological markers, reflecting presumably some kinds of technological aspects of wine making.

Resolution of phenolic antioxidant mixtures employing a voltammetric bio-electronic tongue

This work reports the application of a Bio-Electronic Tongue (BioET) system made from an array of enzymatic biosensors in the analysis of polyphenols, focusing on major polyphenols found in wine. For this, the biosensor array was formed by a set of epoxy-graphite biosensors, bulk-modified with different redox enzymes (tyrosinase and laccase) and copper nanoparticles, aimed at the simultaneous determination of the different polyphenols. Departure information was the set of voltammograms generated with the biosensor array, selecting some characteristic features in order to reduce the data for the Artificial Neural Network (ANN). Finally, after the ANN model optimization, it was used for the resolution and quantification of each compound. Catechol, caffeic acid and catechin formed the three-analyte case study resolved in this work. Good prediction ability was attained, therefore allowing the separate quantification of the three phenols with predicted vs. expected slope better than 0.970 for the external test set (n = 10). Finally, BioET has been also tested with spiked wine samples with good recovery yields (values of 104%, 117% and 122% for catechol, caffeic acid and catechin, respectively).

Antioxidant capacities and phenolic levels of different varieties of Serbian white wines

The biologically active compounds in wine, especially phenolics, are responsible for reduced risk of developing chronic diseases (cardiovascular disease, cancer, diabetes, etc.), due to their antioxidant activities. We determined the contents of total phenolics (TP) and total flavonoids (TF) in selected Serbian white wines by colorimetric methods. Total antioxidant activity (TAA) of the white wines was analyzed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity assay. Medas beli had the highest content of TP, TF and TAA. The radical scavenging capacity (RSC) and total antioxidant activity (TAA) of white wines were 15.30% and 1.055 mM Trolox equivalent, respectively. Total phenolic (TP) and total flavonoid (TF) contents in white wines ranged from 238.3 to 420.6 mg gallic acid equivalent per L of wines and 42.64 to 81.32 mg catechin equivalent per L of wines, respectively. A high and significant correlation between antioxidant activity and total phenolic content was determined in wines (R2 = 0.968, p < 0.01). For the individual polyphenols determination we used a high performance liquid chromatography (HPLC)-diode array detection (DAD) technique. The majority of white wine polyphenols was represent by four hydroxycinnamic acids (HCAs).

A thick-film sensor as a novel device for determination of polyphenols and their antioxidant capacity in white wine

A thick-film electrochemical sensor with an iridium-carbon working electrode was used for determining polyphenols and their antioxidant capacity in white wine. Caffeic acid was used as a model species because it has the ability to produce the highest oxidation current. The correlation coefficient of 0.9975 was obtained between sensor response and caffeic acid content. The total phenolic content (TPC) and scavenging activity on 1,1-diphenyl-2-pycrylhydrazyl (DPPH·) radical were also found to be strongly correlated with the concentration of caffeic acid, with a correlation coefficient of 0.9823 and 0.9958, respectively. The sensor prototype was proven to be a simple, efficient and cost effective device to evaluate the antioxidant capacity of substances.

Comparison of phenolic acids and flavan-3-ols during wine fermentation of grapes with different harvest times

To explore the effects of harvest time on phenolic compounds during wine fermentation, grape berries (Vitis vinifera L. cv. Vidal) were harvested at 17.5, 22.8 and 37.2º Brix and were used to make dry wine, semi-sweet wine and icewine with low alcohol levels, respectively. Phenolic acids and flavan-3-ols were assayed during the fermentation of wines by means of reverse phase-high performance liquid chromatography (RP-HPLC). The results showed that concentrations of most of the phenolic acids and flavan-3-ol in musts increased with harvest time delay and higher total levels of these species were detected in all wines, compared with those measured before fermentation (the total phenolic acid content in wines was 1.5-2.0 fold that of in musts). Except for p-coumaric acid and (-)-epicatechin, other phenolic acids and flavan-3-ols had similar variation patterns (wave-like rise) during fermentation in dry wine and semi-sweet wine. However, some detected compounds, including gentisic acid, p-hydroxybenzoic acid, caffeic acid, p-coumaric acid and sinapic acid showed obviously different trends from the other two wines in the icewine making process. It is thus suggested that the harvest time has a decisive effect on phenols in final wines and influences the evolution of phenolic acids and flavan-3-ols during wine fermentation.

Use of solid-supported liquid-liquid extraction in the analysis of polyphenols in wine

Solid-supported liquid-liquid extraction (SS-LLE) was compared to liquid-liquid extraction (LLE) for the analysis of phenolic compounds in wine. Diatomaceous earth commercial cartridges were evaluated together with "in-house" made cartridges for the wine phenolic extraction. Statistical treatment, analysis of variance ANOVA-single factor, was used to compare the extraction yields obtained by these methods, and for the majority of the studied compounds, significantly higher yields were obtained by the SS-LLE methodology using the "in-house" prepared cartridges. This is an environmentally friendly low-cost sample preparation method which proved to be reproducible (RSD<5% for the most compounds) and yielding high recoveries (80-100%) for the compounds studied.

Determination of free molecular phenolics and catechins in wine by solid phase extraction on polymeric cartridges and liquid chromatography with diode array detection

The use of HLB Oasis polymeric cartridges to extract phenolic acids and aldehydes from red wines has been assayed and compared with the combination of ODS and SAX cartridges. The recoveries on the polymeric cartridges resulted to be notably higher with good precisions. The best operation conditions (cartridge conditioning, sample volume, clean-up and elution) for these latter were selected by experiments carried out on a synthetic wine sample spiked with 14 compounds and on red wine samples. A matrix-matched calibration was advisable to reduce the influence of the matrix in the quantification of the analytes as it was verified from the application of standard addition calibrations on several wine samples. Determination of the analytes in the extracts was performed by reversed-phase HPLC using mobile-phase and flow gradients and detection at 250, 280 and 340 nm.

Changes during storage in conventional and ecological wine: phenolic content and antioxidant activity

Polyphenol content, free radical scavenging capacity, and changes during storage over 7 months in the dark were studied in ecological and conventional red and white wines. In red wines, the most changeable components during storage were the anthocyanins since during storage anthocyanins content decreased 88% in conventional wine and 91% in ecological wine. Initially, the total flavonol contents of the conventional and ecological red wines were 163.88 +/- 2.69 and 153.58 +/- 1.71 mg/L, respectively, and no significant variations occurred during storage. No differences in hydroxycinnamic acid derivatives content between conventional and ecological red and white wines were observed. The flavonol level in white wines was very low, as expected since these compounds are found in grape skin. The initial antioxidant activity was 5.37 +/- 0.14 and 5.82 +/- 0.31 mM equivalents Trolox for conventional and ecological red wines, respectively; no significant differences were observed (p = 0.2831), and these values were 7-8 times higher than the antioxidant activity observed in conventional and ecological white wine. In contrast with other studies, the total concentrations of phenolic compounds in conventional and ecological red and white wines were not related to antioxidant activity (p > 0.05). In red wines, no significant differences were observed in the antioxidant activity of ecological and conventional red wine (p = 0.28), while in white wine significant differences were observed in the antioxidant activity between conventional and ecological white wine (p = 0.006).

Recent advances in capillary electrophoresis methods for food analysis

This review article addresses recent advances in the analysis of foods and food components by capillary electrophoresis (CE). CE has found application to a number of important areas of food analysis, including quantitative chemical analysis of food additives, biochemical analysis of protein composition, and others. The speed, resolution and simplicity of CE, combined with low operating costs, make the technique an attractive option for the development of improved methods of food analysis for the new millennium.

Analysis of phenolic compounds in Spanish Albrariño and Portuguese Alvarinho and Loureiro wines by capillary zone electrophoresis and high-performance liquid chromatography

The concentration of different phenolic compounds was measured in Spanish Albariño and Portuguese Alvarinho and Loureiro white wines by capillary zone electrophoresis (CZE), in order to characterize them. Although all samples presented the same qualitative pattern (characterized by tyrosol; (-)-epicatechin; syringic acid; ferulic acid; p-coumaric acid; caffeic acid, gallic acid; 3,4-dihydroxybenzoic acid; cis-coumaroyl tartaric acid (COUTA); trans-COUTA; trans-caffeoyl tartaric acid (CAFTA), and hydroxycinnamic esters), some quantitative differences were observed. When samples were analyzed by high-performance liquid chromatography (HPLC), in order to compare the results obtained by both techniques, no significant qualitative or quantitative differences were obtained. Nevertheless, CZE proved to be a more convenient technique for the routinary analyses of these wines, due to better separation of the different compounds, better peak shapes, and higher speed than HPLC.