Effects of the Temperature and Ethanol on the Kinetics of Proanthocyanidin Adsorption in Model Wine Systems

Leaching and evolution of anthocyanins and aroma compounds during Cabernet Sauvignon wine fermentation with whole-process skin-seed contact

This study explores the leaching and evolution of anthocyanins and aroma compounds during wine-making, using an industrial-scale vinification of Cabernet Sauvignon with whole-process skin-seed contact. The results indicated that compounds within the same class displayed similar evolutionary patterns during fermentation. The extraction of anthocyanins, C6 aldehydes, and β-damascenes occurred continuously during cold soak, accompanied by the conversion of C6 aldehydes into alcohols and hydrolytic release of glycosidic β-damascenone. During alcoholic fermentation, pyranoanthocyanins, polymeric pigments, esters, benzene compounds, higher alcohols, and acids were generated. The concurrent occurrence of malolactic fermentation and prolonged maceration led to aromas associated with lactic acid bacteria metabolism. Finally, a comparison between free-run wine and pressed wine revealed high concentrations of C6 compounds and polymeric pigments with flavanol dimers in the pressed wine. These results can be used as a reference to optimize the vinification process to enhance the red due and fruity aromas of the wine.

Longer cluster hanging time decreases the impact of grapevine red blotch disease in Vitis vinifera L. Merlot across two seasons

BACKGROUND

Grapevine red blotch virus (GRBV) is a recently discovered virus and a major concern for the wine industry. Prior research indicated that GRBV delays grape ripening by reducing °Brix and anthocyanin concentrations in grapes from infected vines, resulting in higher ethanol concentrations in wines made from healthy fruit compared to diseased vines, which have an impact on sensory properties. In this study, infected fruit (Vitis vinifera L. Merlot) was sequentially harvested (in 2016 and 2017) and chaptalized (in 2017) to ameliorate the impact of GRBV on grape and final wine composition.

RESULTS

Chemical parameters including phenolic and volatile profiles of grapes and their subsequent wines were measured. Sensory properties were determined by descriptive analyses. Results demonstrated that GRBV decreased sugar accumulation and anthocyanin synthesis in grapes. Wines from GRBV grapes harvested at later ripening stage produced wines that were more similar chemically and sensorially to wines made from healthy fruit than to wines made from GRBV fruit harvested earlier.

CONCLUSION

A longer hang time of GRBV grapes is a potential strategy to mitigate the impacts of GRBV. However, chaptalization of diseased fruit must was inefficient at increasing similarities to wines made from healthy fruit. © 2023 Society of Chemical Industry.

Grapevine red blotch virus alters grape skin cell-wall composition impacting phenolic extractability during winemaking

BACKGROUND

Grapevine red blotch virus (GRBV) is the causal agent of grapevine red blotch disease and is known to delay grape ripening. However, grape cell-wall modifications during GRBV infection are largely unknown, even though the cell wall plays a large role in pathogenicity, viral interactions with host plants, and phenolic extractability during winemaking. Understanding the impact of GRBV infection on cell-wall metabolism is important for the development of potential mitigations strategies. In this study, high-throughput transcriptome sequencing was conducted on Vitis vinifera L. 'Merlot' grapes during ripening. The cell-wall composition, phenolic content, and phenolic extractability at two different commercial harvest points were also determined.

RESULTS

Log fold changes indicated a strong induction in diseased grapes at harvest of several transcripts involved in cell-wall solubilization and degradation. However, these observations did not translate to changes in cell-wall composition at either harvest point in diseased grapes, potentially suggesting post-transcriptional regulation. Moderate induction of pectin methylesterase inhibitor transcripts and transcripts associated with pathogenesis-related proteins coincided with increases in pectin and soluble proteins in cell walls of diseased grapes at harvest. Both pectin and pathogenesis-related proteins are known to retain phenolic compounds during winemaking.

CONCLUSION

Our study corroborates this finding when the percentage extractability of flavonols in wines was significantly lower when made from GRBV-infected fruit. These results suggest GRBV alters the grape cell walls, consequently decreasing phenolic extraction during winemaking. © 2023 Society of Chemical Industry.

Impact of the variety on the adsorption of anthocyanins and tannins on grape flesh cell walls

BACKGROUND

During winemaking, after extraction from the skins, anthocyanins and tannins adsorb onto the pulp flesh cell walls. The present study aimed to quantify the amounts adsorbed and their impact on wine composition, the impact of variety and ethanol on adsorption, and whether the presence of anthocyanins plays a role and impacts tannin adsorption.

RESULTS

Anthocyanin and tannin fractions obtained by mimicking winemaking conditions were mixed with fresh flesh cell walls of two varieties: Carignan and Grenache. Adsorption isotherms were measured. Adsorption of tannins was higher with Carignan than with Grenache and decreased when the ethanol content increased. In comparison, anthocyanins were adsorbed in small amounts, and their mixing with tannins had no impact on their adsorption. The differences were related to differences in pulp cell wall composition, particularly in terms of extensins and arabinans.

CONCLUSION

Adsorption of tannins, which can reach 50% of the initial amount, depends on the pulp cell wall composition. This needs to be investigated further. © 2021 Society of Chemical Industry.

Optimization of the Extraction of Proanthocyanidins from Grape Seeds Using Ultrasonication-Assisted Aqueous Ethanol and Evaluation of Anti-Steatosis Activity In Vitro

Conventional extraction methods of proanthocyanidins (PAC) are based on toxic organic solvents, which can raise concerns about the use of extracts in supplemented food and nutraceuticals. Thus, a PAC extraction method was developed for grape seeds (GS) and grape seed powder using food-grade ethanol by optimizing the extraction conditions to generate the maximum yield of PAC. Extraction parameters, % ethanol, solvent: solid (s:s) ratio, sonication time, and temperature were optimized by the central composite design of the response surface method. The yields of PAC under different extraction conditions were quantified by the methylcellulose precipitable tannin assay. The final optimum conditions were 47% ethanol, 10:1 s:s ratio (v:w), 53 min sonication time, and 60 °C extraction temperature. High-performance liquid chromatography analysis revealed the presence of catechin, procyanidin B2, oligomeric and polymeric PAC in the grape seed-proanthocyanidin extracts (GS-PAC). GS-PAC significantly reduced reactive oxygen species and lipid accumulation in the palmitic-acid-induced mouse hepatocytes (AML12) model of steatosis. About 50% of the PAC of the GS was found to be retained in the by-product of wine fermentation. Therefore, the developed ethanol-based extraction method is suitable to produce PAC-rich functional ingredients from grape by-products to be used in supplemented food and nutraceuticals.

Mitigating Grapevine Red Blotch Virus Impact on Final Wine Composition

Grapevine red blotch virus (GRBV), the causative agent of red blotch disease, causes significant decreases in sugar and anthocyanin accumulation in grapes, suggesting a delay in ripening events. Two mitigation strategies were investigated to alleviate the impact of GRBV on wine composition. Wines were made from Cabernet Sauvignon (CS) (Vitis vinifera) grapevines, grafted onto 110R and 420A rootstocks, in 2016 and 2017. A delayed harvest and chaptalization of diseased grapes were employed to decrease chemical and sensory impacts on wines caused by GRBV. Extending the ripening of the diseased fruit produced wines that were overall higher in aroma compounds such as esters and terpenes and alcohol-related (hot and alcohol) sensory attributes compared to wines made from diseased fruit harvested at the same time as healthy fruit. In 2016 only, a longer hangtime of GRBV infected fruit resulted in wines with increased anthocyanin concentrations compared to wines made from GRBV diseased fruit that was harvested at the same time as healthy fruit. Chaptalization of the diseased grapes in 2017 produced wines chemically more similar to wines made from healthy fruit. However, this was not supported by sensory analysis, potentially due to high alcohol content masking aroma characteristics.

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.

Impact of Dry Hopping on Beer Flavor Stability

To investigate the chemical and sensorial impact of dry hopping time on typical pale ale, a standardized beer was produced and separated into ten vessels. Nine vessels were dry hopped, and one vessel remained un-hopped as a control. Impact of dry hopping contact time was investigated over 96 h. Polyphenols and iso-α-acid t/c ratio were analyzed in both Young and Aged beer samples. Total polyphenol content generally increased in both young and aged treatments compared to controls. Analysis of the t/c ratio suggests that both Young and Aged beers were chemically preserved to some degree after approximately 12 h at the given dry hopping rate regardless of age. Within the Aged beer trials, 96 h of dry hop contact yielded a significant increase in t/c ratio compared to all other Aged trials. This suggests that a 4-day dry hop regime may yield additional oxidative protection of iso-α-acids in beers stored unrefrigerated for 30 days. Descriptive analysis was also performed with an 8-person, trained panel; however, beers were sensorially distinguished by their aging time as opposed to their dry hopping time.

Relationship between anthocyanins, proanthocyanidins, and cell wall polysaccharides in grapes and red wines. A current state-of-art review

Numerous research studies have evaluated factors influencing the nature and levels of phenolics and polysaccharides in food matrices. However, in grape and wines most of these works have approach these classes of compounds individually. In recent years, the number of publications interconnecting classes have increased dramatically. The present review relates the last decade's findings on the relationship between phenolics and polysaccharides from grapes, throughout the entire winemaking process up to evaluating the impact of their relationship on the red wine sensory perception. The combination and interconnection of the most recent research studies, from single interactions in model wines to the investigation of the formation of complex macromolecules, brings the perfect story line to relate the relationship between phenolics and polysaccharides from the vineyard to the glass. Grape pectin is highly reactive toward grape and grape derived phenolics. Differences between grape cultivars or changes during grape ripeness will affect the extractability of these compounds into the wines. Therefore, the nature of the grape components will be crucial to understand the subsequent reactions occurring between phenolics and polysaccharide of the corresponding wines. It has been demonstrated that they can form very complex macromolecules which affect wine color, stability and sensory properties.

The Effects of Temperature and Ethanol on Proanthocyanidin Adsorption to Grape Cell Wall Material in the Presence of Anthocyanins

The quantitative and qualitative impacts of anthocyanins on proanthocyanidin adsorption to grape-derived cell wall material were investigated in fifteen unique systems of varying temperatures, ethanol concentrations, and proanthocyanidin concentrations. Proanthocyanidin solutions were exposed to cell wall material and monitored for changes in concentration over 24 h. Increases in both temperature and ethanol resulted in a larger retention of proanthocyanidins in solution and typically faster adsorption kinetics. Analysis of the solution after exposure to cell wall revealed a significant reduction in the molecular weight of proanthocyanidins present in solution, suggesting that anthocyanins do not alter a previously described mechanism of preferentially binding large molecular weight molecules. Additionally, a reduction in polymeric pigment abundance was noted in most conditions, suggesting rapid formation of polymeric pigment in the model solution and preferential adsorption of the polymeric pigment to cell wall material. Compared to a previous study of proanthocyanidin adsorption in the absence of anthocyanins, a significantly larger percentage of proanthocyanidin material was lost via adsorption—up to 70% of available material. In a winemaking context, this may suggest a preferential loss of polymeric pigment via adsorption to cap cell wall material compared to non-pigmented proanthocyanidins and free anthocyanins.

Assessing the Aflatoxins Mitigation Efficacy of Blueberry Pomace Biosorbent in Buffer, Gastrointestinal Fluids and Model Wine

Blueberry (BB) and cherry pomace were investigated as new biosorbents for aflatoxins (AFs) sequestration from buffered solutions, gastrointestinal fluids and model wine. Among the tested biosorbents, BB exhibited the maximum adsorption performance for AFs and hence was further selected for the optimization of experimental parameters like pH, dosage, time and initial concentration of AFs. Material characterizations via scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, N2 adsorption-desorption isothermal studies, thermogravimetric analysis (TGA) and X-ray photon spectroscopy (XPS) techniques revealed useful information about the texture and chemical composition of the biosorbents. The fitting of isothermal data with different models showed the model suitability trend as: Sips model > Langmuir model > Freundlich model, where the theoretical maximum adsorption capacity calculated from the Sips model was 4.6, 2.9, 2.7 and 2.4 mg/g for AFB1, AFB2, AFG1 and AFG2, respectively. Kinetics study revealed the fast AFs uptake by BB (50-90 min) while thermodynamics studies suggested the exothermic nature of the AFs adsorption from both, single as well as multi-toxin buffer systems, gastrointestinal fluids and model wine. Accrediting to the fast and efficient adsorption performance, green and facile fabrication approach and cost-effectiveness, the newly designed BB pomace can be counted as a promising contender for the sequestration of AFs and other organic pollutants.

Chemistry and Reactivity of Tannins in Vitis spp.: A Review

Tannins are a group of polyphenols found in fruits, leaves, trees, etc., well known in the leather industry and in apples, persimmons and grapes, because of their capacity to interact with other polyphenols or other components either from the food product or from saliva. Prior to being able to interact with other compounds, tannins have to be extracted from the food matrix, which depends on their chemistry, as well as the chemical structure of other components, such as cell wall material and proteins. Vitis vinifera grapes are commonly grown around the world and are used in winemaking, providing good quality wines with different levels of tannins responsible for the final wine’s astringency. Many studies have focused on tannins extractability and retention with cell wall material, and the reactivity of tannins with proteins in Vitis vinifera grapes and wine, but there are very few reports for other Vitis species. However, depending on the environmental characteristics of certain regions, Vitis hybrid grapes are grown and used to produce wines more and more. This review focuses on the comparison of the chemistry of tannins, and their reactivity with other macromolecules in Vitis species.

Heat-Dependent Desorption of Proanthocyanidins from Grape-Derived Cell Wall Material under Variable Ethanol Concentrations in Model Wine Systems

Desorption of proanthocyanidins (PA) from grape cell wall material (CWM) was investigated in solutions of varying ethanol concentrations and increasing temperature. The results reveal the reversibility of PA-CWM interactions and the role that temperature and ethanol concentration play in the extent of PA desorption. Sequentially raising temperature from 15 to 35 °C resulted in desorption of up to 48% of the initial adsorbed PA. A comparison to a phenolic extraction model showed significant differences between the predicted and actual amount of PA that desorbed from the CWM. This suggests that the initial conditions of temperature and ethanol concentration must be considered when estimating PA extraction in red wine production. Under typical winemaking conditions, a significant amount of PA may be irreversibly adsorbed if exposed to CWM at low temperature (i.e., cold soak). A compositional analysis suggests the selective desorption of large molecular weight PA from CWM under all experimental conditions. Additionally, a preferential desorption of skin-derived PA over seed-derived PA was noted in the absence of ethanol.

A Mechanistic Model for the Extraction of Phenolics from Grapes During Red Wine Fermentation

Phenolic extraction is a critical part of red wine making. Though empirical models of phenolic extraction kinetics exist, the current level of mechanistic understanding does not allow for accurate predictions. In this work, we propose a mechanistic model for the extraction of phenolics from grape skins and seeds as a function of temperature and ethanol. This model examines the release of phenolics, the adsorption of phenolics onto grape material, and the disappearance of anthocyanins from solution. Additionally, we performed epifluorescence microscopy to explore our finding that seed tannins' release rate appears independent of concentration, and found that the grape seed appears to ablate over fermentation. We also determined the activation energy of anthocyanin disappearance, in good agreement with similar systems. The proposed model results in an excellent fit, and increases the understanding of phenolic extraction and the ability to predict and optimize product outcome in red wine making.