Influence of freezing and heating conditions on grape seed flavan-3-ol extractability, oxidation, and galloylation pattern

In cool-climate viticulture, the short growing season can influence grape seed maturation by reducing the apparent oxidation of flavan-3-ol monomers and associated increase in seed browning. A reduction in seed maturation increases the potential extraction of flavan-3-ol monomers into wine during maceration operations, heightening bitterness. Here, we carried out a 2 × 2 factorial experiment to test the ability of freezing and heating treatments to advance maturation (decrease flavan-3-ol, improve browning) of (Vitis vinifera L.) Pinot noir and Cabernet Sauvignon seeds over a 24-h incubation period. Only freezing significantly increased seed browning in both cultivars. Subsequent correlations with seed flavan-3-ol monomer concentrations suggest that freezing enhanced the oxidation of these compounds. Interestingly, natural ripening and freezing reduced galloylated flavan-3-ol monomers to a greater extent than non-galloylated ones. This study provides new information regarding the susceptibility of flavan-3-ol monomers to freezing and heating, and also suggests that freezing can advance the maturation the seeds of under-ripe red vinifera grapes

Impact of Cluster Thinning on Wine Grape Yield and Fruit Composition: A Review and Meta-Analysis

For wine grape producers, achieving an optimal balance between vegetative and reproductive growth is a key factor in producing high quality fruit and meeting production quotas. This balance is often measured as the leaf-area-to-yield ratio. To increase this ratio, producers often use “cluster thinning” (CT), a management practice involving a selective removal of grape clusters from vines. Despite this, no consensus has been established regarding the optimal CT timing and severity for consistently improving fruit composition. The objective of this work was to identify whether CT “timing” (bloom, pea-size, lag phase, and veraison) or “severity” (15–35%, 36–55%, and 56–75%) influences yield and fruit composition. To achieve this objective, a meta-analysis of 160 publications on CT in grape was reduced to 78 studies via 10 data curation steps. We reported the influence of CT timing and severity on yield and fruit composition, as well as their impact on the yield-fruit composition tradeoff. First, CT timing showed little influence on fruit composition, which provides producers with greater flexibility when using this practice. Second, CT severity was impactful on improving fruit composition (TSS and pH); only the moderate range (36–55%) was effective. In conclusion, wine grape composition is more influenced by CT severity than timing. This work has important implications for grape producers and their approach to improving grape composition

Artificial ripening of grape seed phenolics in Pinot noir and Cabernet Sauvignon

Red Vitis vinifera cultivars are often limited in their performance by climate conditions (e.g., rain, humidity, cold winters, and cool summers). Cool climate viticulture regions are characterized by short growing seasons that reduce fruit quality, limiting technological and phenolic maturity. Management of fruit technological ripening, in vineyard or post-harvest, is pivotal for wine quality. However, the impact of vineyard or cellar practices on seed phenolic fraction remains poorly understood. The aim of our project was to evaluate seed color change, phenolic composition, and their extraction potential after an oxidation induced by a freezing treatment. The freezing treatment was followed by 24 hours of incubation at different temperatures in two Vitis vinifera cultivars: Pinot noir and Cabernet Sauvignon. Results are reporting that the freezing caused the seed color darkening and significant phenolic changes, suggesting similarities with the natural process. The phenolic evolution reported different behaviour between cultivars and compound classes. Most of the changes occurred during the first three hours of incubation, indicating that the oxidation reactions take place at the beginning of the thawing process

Juxtaposition of the Source-to-Sink Ratio and Fruit Exposure to Solar Radiation on cv. Merlot (Vitis vinifera L.) Berry Phenolics in a Cool versus Warm Growing Region

The grapevine source-to-sink ratio and berry exposure to solar radiation both influence grape flavonoid biosynthesis and accumulation. Here, we compared these concepts on cv. Merlot in two different growing locations (Michigan (NH) and Friuli-Venezia Giulia (FVG), IT) to understand whether the environment influences flavonoid sensitivity to these parameters. Three levels of leaf removal (LR0, LR5, LR8) were implemented at the pea-size phenological stage to compare conditions of increased cluster light exposure with a decreasing vine source-to-sink ratio on berry flavonoid accumulation. Treatments did not affect total soluble solids (TSSs) or pH, but titratable acidity (TA) was lower in LR8 at harvest in both locations. LR5 increased anthocyanins and flavonols in MI but decreased most phenolics in FVG. The decreased expression of VviLAR1 and VviF3'5'Hh during ripening supported the lower concentrations of flavan-3-ol monomers and anthocyanins in FVG. In summary, flavonoid biosynthesis and accumulation were more sensitive to solar radiation than the source-to-sink ratio, and the vineyard environment dictated whether solar radiation was beneficial or detrimental to flavonoid biosynthesis

J. agric. food chem.

Removal of basal leaves near blooms inevitably affects grapevine balance and cluster microclimate conditions, improving fruit quality. Mechanization of this practice allows growers to save time and resources, but to our knowledge, it has not yet been compared with the manual application of this practice in a cool-climate region where seasonal temperatures frequently limit fruit technological maturity and phenolic ripening in red Vitis vinifera cultivars. In our research, berry sugar concentration was highest with prebloom mechanical treatment (PB-ME). Furthermore, metabolomics analysis revealed that PB-ME favored the accumulation of significantly more disubstituted anthocyanins and flavonols and OH-substituted anthocyanins compared with manual application. Given that vine balance was similar between treatments, increased ripening with PB-ME is likely due to enhanced microclimate conditions and higher carbon partitioning through a younger canopy containing basal leaf fragments proximal to fruit. This information provides an important strategy for consistently ripening red Vitis vinifera cultivars in cool climates

Increase in seed tannin extractability and oxidation using a freeze-thaw treatment in cool-climate grown red (Vitis vinifera L.) cultivars

Grape seed maturation involves the gradual oxidation of tannins, decreasing excessive bitterness and astringency in wine. In cool climates, this process is limited by the short growing season, affecting wine quality. A “freeze-thaw” treatment on seeds of red vinifera cultivars at veraison and harvest was used to evaluate the effect of oxidation and extractability on seed phenolic fractions. Freezing increased the extraction of total phenolics and o-diphenols quantified from fractionation (fraction 1, vacuolar tannins; fraction 2, hydrogen bonded tannins; fraction 3, covalently bonded tannins), especially at harvest. Despite this, colorimetry, microscopy, oxidation reactivity index (ORI), and correlations between the color index and fractions indicated that freezing disrupted vacuole integrity, enhancing oxidation in the seed coat. In conclusion, vacuolar tannins (which are the main seed phenolics extracted during fermentation) were highly correlated with seed color change, potentially providing information for winemaking in cool climate regions

Yield reduction through cluster or selective berry thinning similarly modulates anthocyanins and proanthocyanidins composition in Refosco dal peduncolo rosso (Vitis vinifera L.) grapes

\u2018Refosco dal peduncolo rosso\u2019 is a late-ripening and low-yielding red grape variety, mainly cultivated in Northeastern Italy (Veneto and Friuli Venezia Giulia), and characterized by relatively high anthocyanins and average-to-low tannins concentrations. Under Friuli\u2019s climatic conditions, it is often challenging to maintain the Refosco dal peduncolo rosso grapes hanging on the vines long enough to match complete berry maturation before the rain season starts. Therefore, winegrowers normally perform cluster thinning in order to enhance or accelerate ripening. This study compared the effects of selective berry thinning (cluster shoulders and tips removal) and classical cluster thinning on fruit technological maturity, anthocyanin profile, and skin and seed proanthocyanidins concentration. Our results revealed that both thinning treatments induced a significant increase in total soluble solids, as well as total anthocyanins through the specific enhancement of OH- and disubstituted monoglucosylated anthocyanins. Additionally, skin high molecular weight proanthocyanidins was reduced by selective berry thinning, while mean degree of polymerization and percentage of galloylation were significantly decreased by both thinning treatments. These results showed that the yield reduction obtained by both methods were profitable to improve the maturation of Refosco dal peduncolo rosso grapes. However, the application of selective berry thinning provided a significant reduction of both skin high molecular weight proanthocyanidins and percentage of prodelphinidins. Therefore, the first evidences on grapes composition favored the cluster thinning technique as less time consuming, but more research on wine and sensory effects is needed to confirm the potential of selective berry thinning

Early Leaf Removal as a Strategy to Improve Ripening and Lower Cluster Rot in Cool Climate (Vitis vinifera L.) Pinot Grigio

Removal of basal leaves early in the vegetative and reproductive development of grapevines is a tool used to decrease fruit set, lower cluster rot severity, and improving fruit quality. However, the considerable time required for implementation limits utilization by grape growers. Efficient mechanization can potentially mitigate these issues, albeit this practice has not yet been compared to manual application at pre-bloom and after-bloom stages in a cool and humid growing region where cluster rot is the major limitation for yield and fruit quality. The goal of this study was to compare mechanical leaf removal (ME) with the manual (MA) removal of six leaves at the pre-bloom (PB) and after-bloom (AB) phenological stages over two seasons in Pinot Grigio (a tight-clustered cultivar). Fruit-set was only decreased in 2017 by PB-MA, however, PB reduced cluster compactness in each season. The loss of fruit to gray mold was lowered by all leaf removal treatments in drier 2017 season, but only MA treatments mitigated loss from sour rot in that year. This indicates that a clear fruit zone and reduced cluster compactness are both needed to lower the impact of cluster rot disease. Only pre-bloom treatments enhanced fruit quality, likely driven by a similar reduction in cluster compactness. The results suggest that PB-ME may be utilized to decrease fruit loss to gray mold in dry seasons and enhance fruit \ub0Brix. Nevertheless, PB-MA can be an effective means to reduce fruit loss to sour rot in drier seasons and enhance ripening in years with high precipitation during veraison. This information provides a single approach to alleviate two prominent issues facing seasonal management strategies in cool climate viticulture

Foliar vs. soil application of Ascophyllum nodosum extracts to improve grapevine water stress tolerance

Biostimulants have recently been used in sustainable agriculture systems to improve plant growth and resilience to biotic and abiotic stress. In this study, foliar (ANEfl) and soil (ANEsl) A. nodosum extract applications were studied to elucidate the impact of different delivery methods on grapevines physiology either under well-watered conditions (WW) or under a water deficit period and a subsequent water recovery (WS). ANEfl increased leaf soluble sugars and photosynthesis of WW vines. Under progressive WS conditions, ANEfl positively impacted leaf gas exchange and water use efficiency (+35 % as compared to untreated vines) at \u3a8stem about -0.65\u202fMPa. Photosynthesis was also improved during the re-watering period (+2.7\u202f\u3bcmol CO2\u202fm 122 s-1) via preserved photochemical efficiency (Fv/Fm +0.19 as compared to untreated vines) and enhanced leaf anatomical and biochemical traits (+8% leaf dry matter and +27.3\u202fmg/g DW of leaf soluble sugars). Contrarily, when soil applied, A. nodosum extracts did not significantly improve vine physiology during the reduced water supply period and only mild effects were detected at re-watering. Results demonstrates that foliar applications of A. nodosum extracts could be an alternative sustainable tool to improve grapevine physiological performances under mild-to-moderate water deficit and to preserve photosystems integrity and vineyard resilience when water limiting conditions get more severe