Grape and wine polymeric polyphenols: Their importance in enology

Ubiquitin ligase VvPUB26 in grapevine promotes proanthocyanidin synthesis and resistance to powdery mildew

Proanthocyanidins (PAs) are an important group of flavonoids that contribute to astringency, color, and flavor in grapes (Vitis vinifera) and wines. They also play a crucial role in enhancing plant resistance to various stresses. However, the underlying regulatory mechanism governing PAs biosynthesis, particularly in relation to conferring resistance to powdery mildew, has not been extensively explored. This study focused on identifying a key player in PAs biosynthesis, namely the plant U-box (PUB) E3 ubiquitin ligase VvPUB26. We discovered that overexpression of VvPUB26 in grapes leads to a significant increase in PAs content, whereas interfering with VvPUB26 has the opposite effect. Additionally, our findings demonstrated that overexpression of VvPUB26 in transgenic grapevines enhances defense against powdery mildew while interfering with VvPUB26 results in increased susceptibility to the pathogen. Interestingly, we observed that VvPUB26 interacts with the WRKY transcription factor VvWRKY24, thereby facilitating ubiquitination and degradation processes. Through RNA-Seq analysis, we found that VvWRKY24 primarily participates in secondary metabolites biosynthesis, metabolic pathways, and plant-pathogen interaction. Notably, VvWRKY24 directly interacts with the promoters of dihydroflavonol-4-reductase (DFR) and leucoanthocyanidin reductase (LAR) to inhibit PAs biosynthesis. Meanwhile, VvWRKY24 also influences the expression of MYB transcription factor genes related to PAs synthesis. In conclusion, our results unveil a regulatory module involving VvPUB26-VvWRKY24-VvDFR/VvLAR that plays a fundamental role in governing PAs biosynthesis in grapevines. These findings enhance our understanding of the relationship between PAs biosynthesis and defense mechanisms against powdery mildew.

Using ethanol as postharvest treatment to increase polyphenols and anthocyanins in wine grape

Red wine grapes are qualitatively evaluated for their content in polyphenols and anthocyanins. Due to certain conditions (weather, latitude, temperature), the concentration of these compounds may be not at the right level for reaching a high-quality wine, thus postharvest technologies can be operated as a remediation strategy. Ethanol is a secondary volatile metabolite and its application has been demonstrated to delay fruit ripening, to reduce decay, and to increase secondary metabolites. The present study investigates the effects of ethanol post-harvest application on wine grapes' metabolism and composition. Red wine grapes (Vitis Vinifera L. cv Aglianico) were exposed to different ethanol doses (0.25, 0.5, or 1 mL L-1) for 12, 24, or 36 h. Ethanol increased sugar concentration, malic acid, free amino nitrogen, polyphenols, and anthocyanins. Particularly, anthocyanins reached an average value of 1820 mg/L in treated samples versus the 1200 mg/L of control grapes already after 12 h whatever the concentration was. Moreover, the highest concentration of ethanol modified berry metabolism shifting from aerobic to anaerobic one. Obtained results suggest that 12 h of ethanol postharvest treatment could be an interesting solution to improve anthocyanins in wine grapes, especially when the quality is not as good as expected.

The effect of probe density coverage on the detection of oenological tannins in quartz crystal microbalance with dissipation monitoring (QCM-D) experiments

BACKGROUND

Polyphenols are a group of compounds found in grapes, musts, and wines. Their levels are crucial for grape ripening, proper must fermentation, and final wine characteristics. Standard chemical analysis is commonly used to detect these compounds, but it is costly, time consuming, and requires specialized laboratories and operators. To address this, this study explores a functionalized acoustic sensor for detecting oenological polyphenols.

RESULTS

The method involves utilizing a quartz crystal microbalance with dissipation monitoring (QCM-D) to detect the target analyte by using a gelatin-based probe layer. The sensor is functionalized by optimizing the probe coverage density to maximize its performance. This is achieved by using 12-mercaptododecanoic acid (12-MCA) to immobilize the probe onto the gold sensor surface, and dithiothreitol (DTT) as a reducing and competitive binding agent. The concentration of 12-MCA and DTT in the solutions is varied to control the probe density. QCM-D measurements demonstrate that the probe density can be effectively adjusted using this approach, ranging from 0.2 × 1013 to 2 × 1013 molecules cm-2 . This study also investigates the interaction between the probe and tannins, confirming the ability of the sensor to detect them. Interestingly, the lower probe coverage achieves higher detection signals when normalized to probe immobilization signals. Moreover, significant changes in mechanical properties of the functionalization layer are observed after the interaction with samples.

CONCLUSION

The combination of QCM-D with gelatin functionalization holds great promise for future applications in the wine industry. It offers real-time monitoring capabilities, requires minimal sample preparation, and provides high sensitivity for quality control purposes. © 2024 Society of Chemical Industry.

Effect of Supplementary Light with Different Wavelengths on Anthocyanin Composition, Sugar Accumulation and Volatile Compound Profiles of Grapes

Protected cultivation is currently one of the main cultivation modes for grape production, but the long-term use of plastic film will have a certain negative impact on the light environment in vineyards, which in turn causes poor colouring, low sugar content and a lack of aroma in some red grape varieties. Supplementing light can be an effective way to mitigate these problems. In this study, vines of three red table grape varieties ('Summer Black', 'Xinyu' and 'Queen Nina') cultivated in a plastic greenhouse were supplemented with red, blue, white and red-blue light from veraison to harvest. All four supplemental light treatments increased the content of anthocyanins, sugars and volatile compounds in three grape varieties compared to CK (no supplemental lighting). Red-blue light treatment was the most favourable for the accumulation of anthocyanins and sugars, and the grapes treated with blue light had the highest content of volatile compounds. The grapes treated with red-blue light all obtained the highest composite scores via principal component analysis. For most of the sensory properties, the highest scores were obtained by the red-blue light-treated grapes. The results of this study will be useful in improving the colouring, sugar, and aroma content of grapes under protected cultivation.

Color Characterization of Bordeaux Red Wines Produced without Added Sulfites

Nowadays, the development of naturalness as a concept is illustrated in the oenological field by the development of wine produced with lower inputs, sometimes even without any addition of SO₂ throughout the winemaking process, up to the bottling stage. Despite the increase in the offer of these wines, they remain poorly explored in the literature and require characterization. This study was developed to evaluate the color of Bordeaux red wines without SO₂ addition using colorimetric and polymeric pigments analysis. From a batch of commercial Bordeaux red wines with and without SO₂ addition, and experimental wines produced from homogenous grapes according to different winemaking processes, colorimetric analyses (CIELab and color intensity (CI)) revealed a large difference in wine color depending on the presence or absence of SO₂. Indeed, wines without SO₂ were significantly darker and presented with a deeper purplish color. According to these observations, polymeric pigments were quantified using UPLC-DAD/ESI QTof, and a higher concentration of polymeric pigments bound by the ethylidene bridge was observed in wines without SO_2. This correlated with differences observed for CIELab and CI. Finally, a comparison with polymeric tannins bound by ethylidene bridge was made and revealed that no differences were observed between wines with and without added SO₂. This underlines the affinity difference between tannins and anthocyanins to react with acetaldehyde to form ethylidene bridges.

Accelerated Solvent Extraction of Phenols from Lyophilised Ground Grape Skins and Seeds

The efficient extraction of phenols from grapes is an important step for their reliable quantification. The aim was to optimise the lyophilisation process and the extraction of phenols from grape skins and seeds. The phenol extraction yield from lyophilised tissues was investigated with different accelerated solvent extraction (ASE) operating conditions. Skins and seeds were separated from frozen berries and lyophilised without being ground. The weight loss during lyophilisation was followed daily. Phenols were extracted from lyophilised, cryo-ground seeds and skins with ASE at room temperature and 10.3 MPa using 80% aqueous acetone and 60% aqueous methanol. The effects of ASE operational parameters (the number of extraction cycles (ECs) and static time (ST) duration) were investigated. The yield of extracted phenols was evaluated spectrophotometrically by determining total phenolic index at 280 nm (TPI). The weight of skins and seeds significantly dropped after 24 h of lyophilisation and continued to decrease, although not significantly, up until the 9th day. The optimal lyophilisation time was estimated to be 3 days and 5 days for skins and seeds, respectively. The phenol extraction yield was significantly affected after changes of ASE conditions. Based on TPI, the optimal ASE conditions were as follows: (i) lyophilised seeds—eight ECs with 10 min ST using aqueous acetone and then four ECs with 20 min ST using aqueous methanol; (ii) lyophilised skins—eight ECs with 1 min ST using aqueous acetone and then one EC with 20 min ST using aqueous methanol.

The effects of regions and the wine aging periods on the condensed tannin profiles and the astringency perceptions of Cabernet Sauvignon wines

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Thirty-two commercial red wines of Cabernet Sauvignon produced in five continuous vintages (2015–2019) and collected from four production regions were statistically different for the analyzed condensed tannin profiles.

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Cabernet Sauvignon wines from four regions were rich in the (–)-epicatechin as the extension subunit.

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Condensed tannin profiles could be used to distinguish some of the production region, but the different vintage samples were not well differentiated.

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A negative correlation of ageing periods and condensed tannin concentration of Cabernet Sauvignon wines was observed.

This study sought to determine the effects of wine-producing regions and aging periods on the astringency and chemistry of condensed tannins of Cabernet Sauvignon dry red wines. A wine quality study was performed with 5 vintages of 32 Cabernet Sauvignon wines produced in four Chinese wine-producing regions, Hebei (H), Xinjiang (X), Inner Mongolia (NM), and Ningxia (NX). Condensed tannin profiles were assessed by high-performance liquid chromatography coupled with a diode array detector (HPLC-DAD). The (–)-epicatechin as the terminal subunit (tEC) is the major differential component between regions. Correlation analysis revealed that condensed tannin concentration and composition significantly affected the sensory evaluation of astringency. Condensed tannin concentrations were significantly and negatively correlated with wine aging periods. However, no significant correlation was found between aging periods and condensed tannin subunits (as mole%) composition. The current findings enhance the understanding of condensed tannins' chemical and astringency characteristics in Cabernet Sauvignon wines.

Composition of Nonextractable Polyphenols from Sweet Cherry Pomace Determined by DART-Orbitrap-HRMS and Their In Vitro and In Vivo Potential Antioxidant, Antiaging, and Neuroprotective Activities

Sweet cherry pomace is an important source of phenolic compounds with beneficial health properties. As after the extraction of phenolic compounds, a phenolic fraction called nonextractable polyphenols (NEPs) remains usually retained in the extraction residue, alkaline and acid hydrolyses and enzymatic-assisted extraction (EAE) were carried out in this work to recover NEPs from the residue of conventional extraction from sweet cherry pomace. In vitro and in vivo evaluation of the antioxidant, antihypertensive, antiaging, and neuroprotective capacities employing Caenorhabditis elegans was achieved for the first time. Extractable phenolic compounds and NEPs were separated and identified by families by high-performance thin-layer chromatography (HPTLC) with UV/Vis detection. A total of 39 phenolic compounds were tentatively identified in all extracts by direct analysis in real-time high-resolution mass spectrometry (DART-Orbitrap-HRMS). EAE extracts presented the highest in vitro and in vivo antioxidant capacity as well as the highest in vivo antiaging and neuroprotective capacities. These results showed that NEPs with interesting biological properties are retained in the extraction residue, being usually underestimated and discarded.

Antioxidant and Wound Healing Potential of Vitis vinifera Seeds Supported by Phytochemical Characterization and Docking Studies

This study explored the in vivo wound healing potential of Vitis vinifera seed extract using an excision wound model with focus on wound healing molecular targets including TGFBR1, VEGF, TNF-α, and IL-1β. The wound healing results revealed that V. vinifera seed extract enhanced wound closure rates (p < 0.001), elevated TGF-β and VEGF levels, and significantly downregulated TNF-α and IL-1β levels in comparison to the Mebo®-treated group. The phenotypical results were supported by biochemical and histopathological findings. Phytochemical investigation yielded a total of 36 compounds including twenty-seven compounds (1−27) identified from seed oil using GC-MS analysis, along with nine isolated compounds. Among the isolated compounds, one new benzofuran dimer (28) along with eight known ones (29−36) were identified. The structure of new compound was elucidated utilizing 1D/2D NMR, with HRESIMS analyses. Moreover, molecular docking experiments were performed to elucidate the molecular targets (TNF-α, TGFBR1, and IL-1β) of the observed wound healing activity. Additionally, the in vitro antioxidant activity of V. vinifera seed extract along with two isolated compounds (ursolic acid 34, and β-sitosterol-3-O-glucopyranoside 36) were explored. Our study highlights the potential of V. vinifera seed extract in wound repair uncovering the most probable mechanisms of action using in silico analysis.

Impact of the Acetaldehyde-Mediated Condensation on the Phenolic Composition and Antioxidant Activity of Vitis vinifera L. Cv. Merlot Wine

Acetaldehyde is a critical reactant on modifying the phenolic profile during red wine aging, suggesting that the acetaldehyde-mediated condensation can be responsible for the variation of antioxidant activity during the aging of this beverage. The present study employs exogenous acetaldehyde at six levels of treatment (7.86 ± 0.10–259.02 ± 4.95 mg/L) before the bottle aging of Merlot wines to encourage phenolic modification. Acetaldehyde and antioxidant activity of wine were evaluated at 0, 15, 30, 45, 60 and 75 days of storage, while monomeric and polymeric phenolics were analyzed at 0, 30 and 75 days of storage. The loss of acetaldehyde was fitted to a first-order reaction model, the rate constant (k) demonstrated that different chemical reaction happened in wines containing a different initial acetaldehyde. The disappearance of monomeric phenolics and the formation of polymeric phenolics induced by acetaldehyde could be divided into two phases, the antioxidant activity of wine did not alter significantly in the first phase, although most monomeric phenolics vanished, but the second phase would dramatically reduce the antioxidant activity of wine. Furthermore, a higher level of acetaldehyde could shorten the reaction time of the first phase. These results indicate that careful vinification handling aiming at controlling the acetaldehyde allows one to maintain prolonged biological activity during wine aging.

Enhancement of anthocyanin and chromatic profiles in 'Cabernet Sauvignon' (Vitis vinifera L.) by foliar nitrogen fertilizer during veraison

BACKGROUND

The influence of foliar nitrogen fertilizer during veraison (FNFV) on anthocyanin accumulation and chromatic characteristics of 'Cabernet Sauvignon' grapes over two seasons was investigated.

RESULTS

Urea and phenylalanine fertilizers (TU and TP, respectively) and a control were sprayed three times at veraison. In 2018, TU displayed a significant enhancement in total individual anthocyanin content and a* and C_ab * profiles. In 2019, FNAV significantly improved the content of total non-acylated, acylated anthocyanin and total individual anthocyanin, and the profiles of L*, a* and C_ab *, except a* in TU. The whole process from phenylalanine variation to anthocyanin accumulation in grape skins was analyzed. On the whole, after the first FNFV to harvest, the increase in phenylalanine metabolism, abscisic acid content, effects of PAL (Phenylalanine ammonia lyase), UFGT (UDP glucose-flavonoid 3-O-glucosyltransferase) and transcript concentrations of VvPAL and VvUFGT involved in anthocyanin biosynthesis were also strong evidence explaining the increased anthocyanin and chromatic profiles in 2019.

CONCLUSION

Overall, FNFV for nitrogen-deficient grapevines could significantly improve grape color, especially in the 2019 veraison with a proper climate. © 2021 Society of Chemical Industry.

Treatment of Winery Wastewater with a Combination of Adsorption and Thermocatalytic Processes

The release of winery wastewater (WW) into the environment, without proper treatment, can cause severe problems to freshwater quality and natural fauna and flora. Therefore, in this work a treatment process was studied, combining adsorption and thermocatalytic oxidation processes. In a more specific way, it optimized the combination of activated sodium bentonite (Na-Mt) and potassium persulfate (KPS)/sodium percarbonate (SPC) as oxidant agents. With the combination of best operational conditions of adsorption ([Na-Mt] = 5.0 g/L, pH = 3.0, V = 500 mL, agitation 350 rpm, T = 298 K, t = 24 h) and thermocatalytic oxidation processes (S2O82−/H2O2 ratio = 1:0.25, S2O82−/H2O2 dosage = 0.1:0.025 (g/g), pH = 7.0, T = 343 K, agitation 350 rpm, t = 2 h), a total organic carbon, chemical oxygen demand and total polyphenols removal of 76.7, 81.4 and >99% was achieved, respectively. Finally, it was evaluated the effect of the treatment processes in the germination index (GI) of different plant seeds. A GI > 80% was achieved, showing a low phytotoxicity effect of the processes applied in the winery wastewater treatment.

Cognitive Keys in Psychophysical Estimation of Chemosensory Perception in University Students

Psychophysical methods allow us to measure the relationship between stimuli and sensory perception. Of these, Detection Threshold (DT) allows us to know the minimum concentration to produce taste identification. Given this, we wonder whether, for example, wine tasting experts are more capable of perceiving their sensory properties than other people, or whether they can distinguish them because they are better able to “describe” them. To verify this, this study analyses the influence of having prior knowledge of the name astringency and, failing that, to detect it and distinguish it between the four basic tastes. One-hundred-and-sixty-two university students with an average age of 19.43 (SD = 2.55) years were assigned to three experimental conditions: an experimental group (G.2) without previous knowledge of the name astringency and with alimentary satiety, and two control groups, both with previous knowledge of the name, these being G.1, with satiety, and G.3, with hunger. DT was collected for the four basic tastes and astringencies. Results showed significant differences in the identification of astringency, being the least identified experimental group with respect to the control groups. It is striking that G.2, without prior knowledge of the name, identified astringency as a bitter taste in most cases. This supports our hypothesis of the importance of attending to linguistic cognitive processes when psychophysically estimating taste in humans.

Ozone and Bioactive Compounds in Grapes and Wine

Ozone is widely used in the agri-food and food processing industries mainly as a sanitizing agent. However, it has recently become clear that ozone exposition leads to another important benefit: in living tissues, the induced-oxidative stress triggers the antioxidant response, and, therefore, it enhances the production of antioxidant and stress-related secondary metabolites. As such, ozone can be considered an abiotic elicitor. The goal of the present review was to critically summarize knowledge about the possibility of improving bioactive compounds and, consequently, the health-related properties of grapes and wine, by using ozone. The greatest interest has been given not only to the pre- and post-harvest treatment of table and wine grapes, but also to the explanation of the mechanisms involved in the ozone-related response and the main secondary metabolites biosynthetic pathways. From the literature available, it is clear that the effect of ozone treatment on health-related properties and secondary metabolites accumulation depends on many factors, such as the cultivar, but also the form (water or gaseous), doses, and application method of ozone. Most of the published papers report an increase in antioxidant compounds (e.g., polyphenols) and stress-related volatiles, confirming the hypothesis that ozone could be used to improve berry and wine compositional and sensory quality.

Red Wine High-Molecular-Weight Polyphenolic Complex: An Emerging Modulator of Human Metabolic Disease Risk and Gut Microbiota

Moderate red wine consumption has been linked to reduced chronic disease risk. Thus far, little has been known about the physicochemical properties and potential biological effects of high-molecular-weight polyphenolic complexes (HPPCs), a major fraction of red wine polyphenols. In this work, the stability and biochemical properties of HPPCs under simulated gastrointestinal conditions in vitro were studied. The results showed that HPPCs were resistant to simulated gastric digestion (SGD) and simulated intestinal digestion (SID). They exhibited significant inhibitory activity against key metabolic syndrome-associated digestive enzymes, achieving 17.1-90.9% inhibition of pancreatic α-amylase, lipase, and cholesterol esterase at 0.02-0.45 mg/mL. HPPCs were metabolized by gut microbiota (GM), leading to significantly enhanced antioxidant capacity when compared with the original, SGD, and SID samples. Furthermore, they favorably modulated GM profiles, which was accompanied by significantly increased short-chain fatty acid generation during the early colonic fermentation phase. These findings suggest that HPPCs are a promising modulator of human metabolic disease risk.

Effects of Water Deficit Irrigation on Phenolic Composition and Antioxidant Activity of Monastrell Grapes under Semiarid Conditions

The high phenolic compound content of grapes makes them an important source of natural antioxidants, among other beneficial health properties. Vineyard irrigation might affect berry composition and quality. Regulated deficit irrigation (RDI) is a widely used strategy to reduce the possible negative impact of irrigation on grapes, improving grape composition and resulting in water savings. Monastrell grapevines (Vitis vinifera L.) grown in eastern Spain were subjected to two water regime strategies: rainfed (non-irrigation) and RDI. The content of anthocyanins, flavonols, flavanols, hydroxybenzoic and hydroxycinnamic acids, and stilbenes was determined by HPLC and was related with total phenolic content and three antioxidant activity methods (ABTS, DPPH, and ORAC). The study aimed to evaluate and compare the phenolic composition and antioxidant potential of Monastrell grapes. The rainfed regime concentrated grapes in terms of phenolic compounds. Thus, total content of anthocyanins, flavonols, flavanols, hydroxybenzoic acids, and total phenols were higher in the rainfed grapes than in the RDI ones. Besides, the rainfed grapes doubled their antioxidant potential with respect to the RDI grapes with the ORAC method. Total phenolic content and antioxidant activity by ORAC assay positively correlated with most of the total phenolic compounds analyzed. This study demonstrates how field practices can modulate final grape composition in relation to their antioxidant activity.

Grape polysaccharides: compositional changes in grapes and wines, possible effects on wine organoleptic properties, and practical control during winemaking

Polysaccharides present in grapes interact with wine sensory-active compounds (polyphenols and volatile compounds) via different mechanisms and can affect wine organoleptic qualities such as astringency, color and aroma. Studies on the role that grape polysaccharides play in wines are reviewed in this paper. First, the composition of grape polysaccharides and their changes during grape ripening, winemaking and aging are introduced. Second, different interaction mechanisms of grape polysaccharides and wine sensory-active compounds (flavanols, anthocyanins and volatiles) are introduced, and the possible effects on wine astringency, color and aroma caused by these interactions are illustrated. Finally, the control of the grape polysaccharide content in practice is discussed, including classical winemaking methods (applying different maceration enzymes, temperature control, co-fermentation, blending), modern vinification technologies (pulsed electric field, ultrasound treatment), and the development of new grape polysaccharide products.

High-Throughput Quantification of 32 Bioactive Antioxidant Phenolic Compounds in Grapes, Wines and Vinification Byproducts by LC-MS/MS

The well-established, health-benefitting effects of grapevines and derivatives (wines and vinification byproducts) are attributed to their antioxidant phenolic content. The dearth of an efficient method for the simultaneous quantitation of antioxidant phenolics prompted us to develop a novel method utilizing triple quadrupole LC-MS/MS for the accurate, fast, simultaneous quantitation of the 32 most abundant grapevine phenolics. The fully validated, novel method is capable to simultaneously record the quantitative presence of 12 phenolic acids, 19 polyphenols and coniferyl aldehyde (a phenolic compound extracted from cork stoppers into wines) and is applicable for the determination of antioxidant phenolics content of grape berries, pomace, stems and wines. Its utility was demonstrated for three native Greek grapevine varieties, two red (Mandilaria and Aidani mavro) and one white (Monemvassia). Results herein highlighted the stems of the Monemvassia white variety as particularly rich in antioxidant phenolics such as the flavonol monomer (+)-catechin (387 mg/kg) and the dimer procyanidin B1 (400 mg/kg) along with stilbene phytoalexin trans-resveratrol (24 mg/kg). These results are in line with the TPC, TFC and TTC content of stems and the determined antioxidant capacities, highlighting the stems of this Vitis vinifera variety as potentially exploitable source of antioxidant phenolics.

Focus on the role of seed tannins and pectolytic enzymes in the color development of Pinot noir wine

Maceration techniques which promote the extraction of color pigments and tannin from grapes are often sought in Pinot noir winemaking to optimise color stability; alternatively, exogenous grape tannins may be included during fermentation. To examine the effect of seed-derived tannins and the use of pectolytic enzymes on color development in wines, conventional must preparations of Vitis vinifera L. cv Pinot noir grapes were compared with wines made using a supplementary addition of either a commercial seed tannin product or previously fermented seeds, while in a complementary experiment, seeds were sequentially removed during fermentation. After 6 months bottle aging, wines supplemented with either a commercial seed tannin solution (0.4 ​g/L), or fermented seeds (20% w/w seeds) had from 60% to 95% higher tannin concentration than the untreated wine, and up to 60% more monomeric anthocyanins. Conversely, when a third of the seeds were removed from the fermenting wine, the concentration of both tannin and non-bleachable pigments was 20-30% lower than in untreated wines and the wine hue had more red-purple tones. Exploration of the use of pectolytic enzymes in conjunction with seed removal was also found to have a significant impact on wine color parameters. Further insights on the timing of egress of tannin precursors from seeds was obtained from histochemical examination of the seeds that had been removed during alcoholic fermentation.

Wine phenolic profile altered by yeast: Mechanisms and influences

Grape phenolic compounds undergo various types of transformations during winemaking under the influences of yeasts, which further impacts the sensory attributes, thus the quality of wine. Understanding the roles of yeasts in phenolics transformation is important for controlling wine quality through fermentation culture selection. This literature review discusses the mechanisms of how yeasts alter the phenolic compounds during winemaking, summarizes the effects of Saccharomyces cerevisiae and non-Saccharomyces yeasts on the content and composition of phenolics in wine, and highlights the influences of mixed cultural fermentation on the phenolic profile of wine. Collectively, this paper aims to provide a deeper understanding on yeast-phenolics interactions and to identify the current literature gaps for future research.

Influence of seaweed foliar application to Tempranillo grapevines on grape and wine phenolic compounds over two vintages

The study of seaweeds is increasing in viticulture due to their implications on plant protection and grape quality. This trial aimed to study the effects of foliar applications of an Ascophyllum nodosum extract at low (0.25%, v v-1) and high (0.50%, v v-1) dosages on grape and wine phenolic compounds in 2017 and 2018. In grapes, seaweed biostimulation increased the content of malvidin-3-glc, myricetin-3-glc and myricetin-3-gal in 2017 season. Moreover, both treatments improved the synthesis of trans-piceid and total stilbenes in both seasons. Sensory analysis revealed that 2017 wines had more color than the 2018 wines, which coincided with color intensity parameters. Therefore, seaweed applications to grapevines improved stilbenes content in grapes independently of the season and its effects on the rest of phenolic compounds in grapes and wines depended strongly of season factor.

Phenolic Profiles of Red Wine Relate to Vascular Endothelial Benefits Mediated by SIRT1 and SIRT6

Dietary phenolic compounds possess potent bioactivity against inflammatory pathways of chronic inflammatory conditions, such as type 2 diabetes. Here, the phenolic profile and bioactivity of Italian red wines Gaglioppo, Magliocco, and Nerello Mascalese were characterized. NMR, HPLC/UV-Vis and spectrophotometric characterization showed that Magliocco was the richest wine in monomeric anthocyanins (two-fold), catechins, and low molecular weight phenolics (LMWP). A positive correlation was observed between the polyphenolic content and antioxidant capacity (p < 0.05), with Magliocco displaying the highest antioxidant capacity (p < 0.01). In vitro evidence on the endothelial cell models of insulin resistance and hyperglycemia showed the ability of Magliocco to reduce reactive oxygen species (ROS) (p < 0.01) and cytokine release (p < 0.01) and to upregulate SIRT1 and SIRT6 (p < 0.01). On the whole, the results indicated that the quantitative and qualitative phenolic profiles of red wines influence their in vitro beneficial effects on oxidative and proinflammatory milieu in endothelial cells, showing a positive modulation of SIRT1 and SIRT6, both implied in vascular aging.

Wine Polyphenols and Health: Quantitative Research Literature Analysis

The relationship between wine polyphenols and health has been receiving growing scientific attention in the last few years. To confirm this point, the proposed paper identifies the major contributors to academic journals regarding the relationships between wine polyphenols and health. The endpoints of the proposed study are to provide a comprehensive overview and analysis of the literature regarding the relationships between wine polyphenol and health based on a bibliometric analysis. Bibliometric data were extracted from the Scopus online database using the search string TITLE-ABS-KEY (wine AND polyphenol* AND health OR (“french paradox” OR “cardiovascular disease*” OR atherosclerosis OR microbiota) and analyzed using the VOSviewer bibliometric software to generate bubble maps and to visualize the obtained results. This perspective paper analyzes: (i) the research themes addressing the relationships between wine polyphenols and health; (ii) the major contributors’ origin, e.g., country and/or regions; (iii) the institutions where the research is based; (iv) the authors; and (v) the type of paper. These results represent a useful tool to identify emerging research directions, collaboration networks, and suggestions for more in-depth literature searches.

The Pro-Oxidant Activity of Red Wine Polyphenols Induces an Adaptive Antioxidant Response in Human Erythrocytes

The protective effect of dealcoholized red wine on human health has been partially associated with its polyphenolic components, suggesting that the pool of polyphenols, including flavonoids and anthocyanins, can be responsible for the functional effects of this beverage. We hypothesize a new role of red wine polyphenols (RWp) in modulating the antioxidant potential of erythrocytes, protecting them against oxidative stress. We previously demonstrated that RWp activated the Plasma Membrane Redox System (PMRS), which is involved in neutralizing plasma free radicals. Here, we investigated the underlying mechanism triggered by RWp in the activation of PMRS via the involvement of GSH. Hence, treatment of human erythrocytes with RWp (73 μg/mL Gallic Acid Equivalents) increased GSH intracellular concentration, which depends upon the activation of glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G6PD), whose enzymatic activities increase of about 30% and 47%, respectively. Changes in the GSH pathway induced by RWp were associated with a slight but significant increase in reactive oxygen species (ROS). We conclude that the pro-oxidant effect of RWp promoted an adaptive stress response in human erythrocytes, which enhances their antioxidant defense.

Effects of Huangjiu, Baijiu and Red Wine Combined With High-Fat Diet on Glucose and Lipid Metabolism: Aggravate or Alleviate?

AIM

To compare effects on certain health indices in rodents of different doses of alcoholic beverages, huangjiu (Chinese yellow wine), red wine and baijiu (Chinese liquor) combined with high-fat diet (HFD) and the pure HFD.

METHODS

A total of 80 rats were randomly divided into eight groups and treated with (a) basal diet (3.5 kcal/g); (b) HFD (19.5% w/w lard, 4.5 kcal/g) and (c) HFD with low or high doses of separate alcoholic beverages (2.5 and 5 g/kg ethanol, respectively) for 28 weeks.

RESULTS

Chronic drinking when combined with HFD was associated with reduced body weight, fat accumulation and serum TNF-α level, serum TG, TC and LDL-C levels, and improved glucose tolerance (OGTT) and insulin sensitivity (ITT), hepatic enzymes; elevated levels or activities of the antioxidant enzymes like superoxide dismutase, catalase and glutathione reductase, reduced the content of lipid peroxidation productions such as malondialdehyde, in comparison with the pure HFD intake. In addition, compared with HFD, drinking plus HFD improved microbiota dysbiosis, down-regulated the ratio of Firmicutes/Bacteroidetes and promoted the growth of some probiotics including Prevotellaceae_UCG-001 and norank_f__Bacteroidales_S24-7_group.

CONCLUSION

Overall, the three beverages showed different impacts on indicators but red wine showed the most 'beneficial' effects. Of course, higher ethanol dosages can be expected to cause overall negative health effects, and harms of high fat intake can be prevented by healthier diet.

Proteomic profile of the acquired enamel pellicle of professional wine tasters with erosive tooth wear

The aim of this study was to compare the acquired enamel pellicle protein profile of professional wine tasters with mild and moderate erosive tooth wear. Twelve professional wine tasters participated (3 from a low tooth wear group; 9 from a high tooth wear group). Acquired enamel pellicle samples were collected and processed for proteomic analysis (nLC-ESI-MS/MS). The acquired enamel pellicle proteomic profile was different between the groups. The proteins found exclusively in the low tooth wear group were histatins 1 and 3 and mucins 7 and 21. When comparing the wear groups, proteins with higher levels in the low tooth wear group included neutrophil defensins (1 and 3), lysozyme C, lysozyme, myeloperoxidase, and squalene monooxygenase. In conclusion, the findings indicate that the proteins found at higher levels in the low tooth wear group and proteins exclusively found in the low tooth wear group might be protective and, therefore, could be good candidates for further studies regarding their potential to be added to dental products to protect professional wine tasters from extrinsic erosive tooth wear.

Using foliar nitrogen application during veraison to improve the flavor components of grape and wine

Nitrogen is involved in the winemaking process from grapevine growth to wine fermentation, and its precise utilization in vineyards can regulate grape and wine quality. Foliar nitrogen application during veraison (FNAV) could prevent nitrogen deficiency in grape and must in nitrogen-deficient vineyards. Moreover, FNAV also could improve certain flavor components of grape and wine, but little attention has been paid to FNAV. Therefore, this paper mainly reviews the difficulties encountered in current applications of nitrogen in vineyards and wineries, and the advantages of FNAV over the addition of nitrogen in soil and wineries. And it discusses that FNAV can increase yeast-assimilable nitrogen and phenolics, and scarcely affect volatile components of grape (must and wine), and points out the existing problems including the core issue and then puts forward future research directions. This information may indicate future directions for research, and provide a reference for viticulturists and winemakers on the precise application of nitrogen on grapevine and must to further improve grape and wine quality in nitrogen-deficient vineyards. © 2020 Society of Chemical Industry.

A Review on Stems Composition and Their Impact on Wine Quality

Often blamed for bringing green aromas and astringency to wines, the use of stems is also empirically known to improve the aromatic complexity and freshness of some wines. Although applied in different wine-growing regions, stems use remains mainly experimental at a cellar level. Few studies have specifically focused on the compounds extracted from stems during fermentation and maceration and their potential impact on the must and wine matrices. We identified current knowledge on stem chemical composition and inventoried the compounds likely to be released during maceration to consider their theoretical impact. In addition, we investigated existing studies that examined the impact of either single stems or whole clusters on the wine quality. Many parameters influence stems' effect on the wine, especially grape variety, stem state, how stems are incorporated, when they are added, and contact duration. Other rarely considered factors may also have an impact, including vintage and ripening conditions, which could affect the lignification of the stem.

Wine Polyphenol Content and Its Influence on Wine Quality and Properties: A Review

Wine is one of the most consumed beverages around the world. It is composed of alcohols, sugars, acids, minerals, proteins and other compounds, such as organic acids and volatile and phenolic compounds (also called polyphenols). Polyphenols have been shown to be highly related to both (i) wine quality (color, flavor, and taste) and (ii) health-promoting properties (antioxidant and cardioprotective among others). Polyphenols can be grouped into two big families: (i) Flavonoids, including anthocyanidins, flavonols, flavanols, hydrolysable and condensed tannins, flavanones, flavones and chalcones; and (ii) Non-flavonoids, including hydroxycinnamic acids, hydroxybenzoic acids, stilbenes, tyrosol and hydroxytyrosol. Each group affects in some way the different properties of wine to a greater or a lesser extent. For that reason, the phenolic composition can be managed to obtain singular wines with specific, desirable characteristics. The current review presents a summary of the ways in which the phenolic composition of wine can be modulated, including (a) invariable factors such as variety, field management or climatic conditions; (b) pre-fermentative strategies such as maceration, thermovinification and pulsed electric field; (c) fermentative strategies such as the use of different yeasts and bacteria; and (d) post-fermentative strategies such as maceration, fining agents and aging. Finally, the different extraction methods and analytical techniques used for polyphenol detection and quantification have been also reviewed.

Interactions between Polyphenols and Volatile Compounds in Wine: A Literature Review on Physicochemical and Sensory Insights

Wine polyphenols (PPhs) and volatile organic compounds (VOCs) are responsible for two of the main sensory characteristics in defining the complexity and quality of red wines: astringency and aroma. Wine VOCs’ volatility and solubility are strongly influenced by the matrix composition, including the interactions with PPhs. To date, these interactions have not been deeply studied, although the topic is of great interest in oenology. This article reviews the available knowledge on the main physicochemical and sensory effects of polyphenols on the release and perception of wine aromas in orthonasal and retronasal conditions. It describes the molecular insights and the phenomena that can modify VOCs behavior, according to the different chemical classes. It introduces the possible impact of saliva on aroma release and perception through the modulation of polyphenols–aroma compounds interactions. Limitations and possible gaps to overcome are presented together with updated approaches used to investigate those interactions and their effects, as well as future perspectives on the subject.

Foliar Phenylalanine Application Promoted Antioxidant Activities in Cabernet Sauvignon by Regulating Phenolic Biosynthesis

The effects of foliar phenylalanine application during veraison (FPV) on phenolic biosynthesis and correlation between phenolic compositions and antioxidant activities in Cabernet Sauvignon grown in field and greenhouse were investigated. Solutions with 69 and 138 mg N/vine phenylalanine (Pe1 and Pe2, respectively) and an aqueous solution without nitrogen (CK) were sprayed three times during veraison. FPV significantly improved antioxidant activities in grapes using the two culture methods. The most contributory phenolic compositions to antioxidant activities were anthocyanins and stilbenes following FPV compared with CK. Phenylalanine metabolism, abscisic acid content, and expression levels of VvPAL, VvCHS, VvF3H, VvUFGT, and VvSTS in the phenolic synthesis pathway were increased from the first FPV to harvest. Although Pe2 significantly increased total phenolic contents than Pe1, antioxidant parameters were not markedly affected by the phenylalanine dose. Our finding revealed that FPV was a useful fertilization method to enhance antioxidant activities in grapes in nitrogen-deficient vineyards.

Characterization of Anthocyanins and Anthocyanin-Derivatives in Red Wines during Ageing in Custom Oxygenation Oak Wood Barrels

The ageing of wines in oak barrels is a key stage in the production of high-quality red wines, with the type of oak chosen and the amount of oxygen received by the wine being the determining factors of the process. This work analyses the effect of ageing the same red wine in barrels with different oxygenation rates for one year (OTR), specifically the effect on the evolution of anthocyanins, their derivatives and the appearance of new pigments according to the oxygen dosage in barrels. Results show that wines aged in High-Wood-OTR barrels have a large quantity of monomeric anthocyanins and wine aged in Low-Wood-OTR barrels presents a major intensity of colour. Moreover, using LC-MS analysis, it was possible to detect and identify different families of anthocyanin derivatives, including the tentative identification of two new aldehyde-flavanol-methylpyranoanthocyanin pigments.

Ochratoxin A presence in Cabernet Sauvignon wine changes antioxidant activity in vitro and oxidative stress markers in vivo

Ochratoxin A (OTA) is a mycotoxin found in grape products and oxidative stress has been reported as an important mechanism involved in its toxicity, classified as possible carcinogenic to humans. Conversely, phenolics are known bioactive compounds in grapes and display great antioxidant properties. However, the biological effects of the concomitant presence of phenolic compounds and OTA remains unclear. The aim of this study was to evaluate, for the first time, the effect of OTA presence in Cabernet Sauvignon wine on antioxidant activity in vitro and on oxidative stress markers in vivo. In addition, the phenolic composition of wine was evaluated by LC-DAD-MS/MS. In vitro assays were based on spectrophotometric methods, while in vivo assays were performed evaluating oxidative stress markers in the nematode Caenorhabditis elegans, an alternative model to animal testing. A total of 23 phenolic compounds were identified in the Cabernet sauvignon red wine, including the anthocyanins delphinidin-3-O-glicoside and malvidin-3-O-glicoside, the flavonol quercetin-3-O-glucuronide and the phenolic acids caffeic, verbascoside and caftaric. Trans-resveratrol and trans-piceid were the only stilbenes found in the samples. OTA presence in the red wine was accompanied by reduction in GSH content and increase in hydroxyl radical generation in vitro. The presence of OTA in wine also increased lipoperoxidation and induced overexpression of the antioxidant enzymes superoxide dismutase and catalase in vivo. This study demonstrates that OTA presence in red wine can reduce its antioxidant potential in vitro and induces oxidative stress in vivo, without affecting the phenolic compounds levels in the samples. Thus, this work provides insights into the negative effects of the presence of OTA in wine, not only by its known toxicity, but also by prejudicing the antioxidant potential of wine. It is important to be aware of these effects when developing a complete description of OTA toxicity in humans.

Simultaneous determination of phenolic metabolites in Chinese citrus and grape cultivars

Background

As the major bioactive compounds in citrus and grape, it is significant to use the contents of flavonoids and phenolic acids as quality evaluation criteria to provide a better view of classifying the quality and understanding the potential health benefits of each fruit variety.

Methods

A total of 15 varieties of citrus and 12 varieties of grapes were collected from Fujian, China. High-performance liquid chromatography method was used for the simultaneous determination of 17 phenolic compounds, including gallic acid, chlorogenic acid, caffeic acid, syringic acid, ρ-coumaric acid, ferulic acid, benzoic acid, salicylic acid, catechin, epicatechin, resveratrol, rutin, naringin, hesperidin, quercetin, nobiletin and tangeritin in the peels of citrus and grape cultivars. Further, the cultivars of citrus and grape were classified using principal component analysis (PCA) and hierarchical cluster analysis (HCA).

Results

A thorough separation of the 17 compounds was achieved within 100 min. The tested method exhibited good linearity (the limits of detection and limits of quantification were in the range of 0.03–1.83 µg/mL and 0.09–5.55 µg/mL, respectively), precision (the relative standard deviations of repeatability were 1.02–1.97%), and recovery (92.2–102.82%) for all the compounds, which could be used for the simultaneous determination of phenolic compounds in citrus and grape. Hesperidin (12.93–26,160.98 µg/g DW) and salicylic acid (5.35–751.02 µg/g DW) were the main flavonoids and phenolic acids in 15 citrus varieties, respectively. Besides, the hesperidin (ND to 605.48 µg/g DW) and salicylic acid (ND to 1,461.79 µg/g DW) were found as the highest flavonoid and the most abundant phenolic acid in grapes, respectively. A total of 15 citrus and 12 grape samples were classified into two main groups by PCA and HCA with strong consistency.

Oenological potential and health benefits of Chinese non-Vitis vinifera species: An opportunity to the revalorization and to breed new varieties

The wine industry is focused on the producing wine mostly from European grapevine varieties (Vitis vinifera L.). China has experienced a significant growth of the vineyard surface, based on the cultivation of these grapevine varieties. Currently, China has become one of the countries with the largest surface of planted vineyards in the world. In the last years, there has been a trend to oenologically and viticulturally revalorize certain autochthonous grapevine species. China holds a great diversity of Vitis species, which are being the focus of study. This could be an important alternative for the diversification of wine production, providing new products with a strong identity. Additionally, the varietal homogenization has increased the vineyard genetic vulnerability in relation to the emergence of grapevine diseases and their resistance to chemical fungicides. In this way, non-Vitis vinifera species are characterized by having a high resistance to a wide range of biotic and abiotic factors, which can bring an opportunity to breed new varieties. However, there is little available information about the oenological potential of these species, which makes it a current interesting topic. Therefore, this review aims to summarize the oenological potential of non-Vitis vinifera species found in China, discussing their potential effects on human health and thus, to propose some Chinese wild grapes for their use in breeding programs.

Grape skins as supplements for color development in Pinot noir wine

A particular challenge to making wine from Pinot noir grapes is the delicate flavor, light color and poor ageing potential of the wine. Conventional Pinot noir must preparations were compared with those made using a skin-based supplement to assess the impact on non-bleachable (sulfur resistant) pigments in the wine. When supplemented with either fresh grape pomace of Pinot noir, Pinot gris or Chardonnay grapes; Pinot noir grape marc or a commercial liquid grape skin extract, the additional seeds and pulp from the supplements were shown to compromise the development of stable pigments in the wine. To compare the relative merits of tannin derived from grape skins and seeds, the supplements used in a parallel experiment were the skins alone of the same three grape varieties and at six months bottle age, the stable pigment concentration was found to exceed the amount attributable to the supplement. A third experiment used fermented grape skins as the supplement, with 85% of the supplementary anthocyanin recovered as stable pigment complexes in the wine. Notably, this series of experiments showed that supplements containing grape seeds appeared to compromise non-bleachable pigment formation in the wine while skin only supplements stimulated their development.

Effect of tannin addition on chromatic characteristics, sensory qualities and antioxidant activities of red wines

Tannin addition as an enological practice has been widely used in the winemaking process because of their ability of improving the aroma and sensory characteristics and stabilizing of color of red wine. In this study, hydrolysable, condensed tannins and their mixtures in different ratios were added into two Merlot wines to investigate their effect on the wine overall quality. The contents of 15 phenolic compounds were detected by HPLC-DAD, CIELAB color parameters were measured using a chromatic aberration meter, sensory evaluation was accomplished using the assessment standards established by the American Wine Association, and antioxidant activities were analyzed using DPPH and ABTS radical tests. The results indicated that adding tannins affected phenolic composition, contents and color of wine. The specific effects varied by tannins. Furthermore, tannin addition, especially the mixed tannins, improved the sensory qualities and antioxidant activities greatly. The mixed tannins added with a ratio of 1 : 1 between hydrolyzable and condensed tannins exhibited a better effect on both sensory qualities and antioxidant activities, and it could be recommended as an ideal tannin addition for wine quality improvement.

The effect of tannin addition on the wine overall quality were investigated and an ideal tannin addition was recommended for wine quality improving.

Investigation of the safety grapeseed powder as an alternative to cocoa-powder in a confectionery glaze

The article considers the safety and environmental cleanliness of grapeseed powders compared to the natural and alkalized cocoa powders. The content of heavy metals in the investigated powders has been determined by the atomic adsorption method; radionuclide activity has been determined by the spectrometric method; the presence of mycotoxins B1, T-2-toxin, zearalenone, and deoxynivalenol (vomitoxin) has been determined by thin-layer chromatography; the amount of nitrates has been determined by the ionometric method; contamination of powders with organophosphorous and organochlorine  pesticides has been determined by chromatographic method.  According to the results of experiments, the content of heavy metals in all investigated powders is within the limits of the maximum permissible concentration, whilst powders of grapeseeds are notable for a significantly lower mass content of plumbum, zinc, copper salts. As for the radioactivity of grapeseed powders, the activity of radionuclides is significantly below the permissible level. Presence of aflatoxin В1 has been detected in the alkalized cocoa powder sample, of zearalenone – in the grapeseed powder oilcake sample. Their concentration does not exceed the allowable concentration. Mycotoxines are absent in other samples investigated. Concentration of nitrates in the natural and alkalized cocoa powder samples is by 20–30 times higher than that found in grapeseed powders. The content of organophosphorous and organochlorine  pesticides in all cocoa powder samples and all grapeseed containing powders is below the method’s threshold of detectability. The glaze samples containing the additives investigated have a considerably lower content of heavy metals compared to the reference samples. Glaze with cocoa powder partially replaced with grapeseed powders has high organoleptic quality parameters. During the glazing process, it is applied on the surface of products in thin layers and cools down in small waves. The results obtained prove that domestic raw materials are safe for human health, and confectionery glaze containing grapeseed powders as partial replacement of the cocoa powder has high safety characteristics.

Preparation and Antioxidant Activity of Ethyl-Linked Anthocyanin-Flavanol Pigments from Model Wine Solutions

Anthocyanin-flavanol pigments, formed during red wine fermentation and storage by condensation reactions between anthocyanins and flavanols (monomers, oligomers, and polymers), are one of the major groups of polyphenols in aged red wine. However, knowledge of their biological activities is lacking. This is probably due to the structural diversity and complexity of these molecules, which makes the large-scale separation and isolation of the individual compounds very difficult, thus restricting their further study. In this study, anthocyanins (i.e., malvidin-3-glucoside, cyanidin-3-glucoside, and peonidin-3-glucoside) and (–)-epicatechin were first isolated at a preparative scale by high-speed counter-current chromatography. The condensation reaction between each of the isolated anthocyanins and (–)-epicatechin, mediated by acetaldehyde, was conducted in model wine solutions to obtain ethyl-linked anthocyanin-flavanol pigments. The effects of pH, molar ratio, and temperature on the reaction rate were investigated, and the reaction conditions of pH 1.7, molar ratio 1:6:10 (anthocyanin/(–)-epicatechin/acetaldehyde), and reaction temperature of 35 °C were identified as optimal for conversion of anthocyanins to ethyl-linked anthocyanin-flavanol pigments. Six ethyl-linked anthocyanin-flavanol pigments were isolated in larger quantities and collected under optimal reaction conditions, and their chemical structures were identified by HPLC-QTOF-MS and ECD analyses. Furthermore, DPPH, ABTS, and FRAP assays indicate that ethyl-linked anthocyanin-flavanol pigments show stronger antioxidant activities than their precursor anthocyanins.

Astringency, bitterness and color changes in dry red wines before and during oak barrel aging: An updated phenolic perspective review

To understand effects of using oak barrels on the astringency, bitterness and color of dry red wines, phenolic reactions in wines before and after barrel aging are reviewed in this paper, which has been divided into three sections. The first section includes an introduction to chemical reactivities of grape-derived phenolic compounds, a summary of the phenolic reactions that occur in dry red wines before barrel aging, and a discussion of the effects of these reactions on wine astringency, bitterness and color. The second section introduces barrel types that determine the oak barrel constituents in wines (primarily oak aldehydes and ellagitannins) and presents reactions between the oak constituents and grape-derived phenolic compounds that may modulate wine astringency, bitterness and color. The final section illustrates the chemical differences between basic oxidation and over-oxidation in wines, discusses oxygen consumption kinetics in wines during barrel aging by comparing different oxygen consumption kinetics observed previously by others, and speculates on the possible preliminary phenolic reactions that occur in dry red wines during oak barrel aging that soften tannins and stabilize pigments via basic oxidation. Additionally, sulfur dioxide (SO₂) addition during barrel aging and suitability of adopting oak barrels for aging wines are briefly discussed.