Utilization of a freeze-thaw treatment to enhance phenolic ripening and tannin oxidation of grape seeds in red (Vitis vinifera L.) cultivars

Microclimate of Grape Bunch and Sunburn of White Grape Berries: Effect on Wine Quality

This research aimed to evaluate the composition of wines made with white grapes which are particularly susceptible to sunburn symptoms due to the absence of anthocyanin. Sunburn is a complex physiological dysfunction leading to browning or necrosis of berry tissues. In vintage 2021, the canopy of 'Verdeca' grapevines grown in Salento, South Italy, was differently managed by sun exposing or shading the bunches. Micrometeorological conditions were studied at different levels. Grapes were vinified, comparing the winemaking with and without skin maceration. The vegetative-productive balance of plants was not substantially modified. On the contrary, a significant effect was observed on the quality and quantity of grapes produced: smaller berries with sunburn symptoms were found on unshaded bunches. This influenced the percentage distribution among skin, pulp and seeds, causing a decrease in must yield of up to 30%. The pH was significantly higher in macerated wines made using shaded grapes, due to a lower titratable acidity and to significant impacts on the acid profile. Obviously, maceration produced a higher extraction of phenolics in wines, which reached their maximum in wines made with sunburned grapes. The absorbance at 420 nm, index of yellow color, was also significantly higher in sunburned grapes, indicating greater oxidation. Even though excessive grape sun-exposure could negatively affect the perception of white wines made without maceration (resulting in more oxidative character), the sensory quality of orange/amber wines was not significantly impacted by the presence of sunburned grapes. Thus, this winemaking technique could be particularly interesting to set up a production strategy adapted to viticultural regions strongly affected by climate change.

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.

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.

Past and Future of Plant Stress Detection: An Overview From Remote Sensing to Positron Emission Tomography

Plant stress detection is considered one of the most critical areas for the improvement of crop yield in the compelling worldwide scenario, dictated by both the climate change and the geopolitical consequences of the Covid-19 epidemics. A complicated interconnection of biotic and abiotic stressors affect plant growth, including water, salt, temperature, light exposure, nutrients availability, agrochemicals, air and soil pollutants, pests and diseases. In facing this extended panorama, the technology choice is manifold. On the one hand, quantitative methods, such as metabolomics, provide very sensitive indicators of most of the stressors, with the drawback of a disruptive approach, which prevents follow up and dynamical studies. On the other hand qualitative methods, such as fluorescence, thermography and VIS/NIR reflectance, provide a non-disruptive view of the action of the stressors in plants, even across large fields, with the drawback of a poor accuracy. When looking at the spatial scale, the effect of stress may imply modifications from DNA level (nanometers) up to cell (micrometers), full plant (millimeters to meters), and entire field (kilometers). While quantitative techniques are sensitive to the smallest scales, only qualitative approaches can be used for the larger ones. Emerging technologies from nuclear and medical physics, such as computed tomography, magnetic resonance imaging and positron emission tomography, are expected to bridge the gap of quantitative non-disruptive morphologic and functional measurements at larger scale. In this review we analyze the landscape of the different technologies nowadays available, showing the benefits of each approach in plant stress detection, with a particular focus on the gaps, which will be filled in the nearby future by the emerging nuclear physics approaches to agriculture.

Georgian Grapevine Cultivars: Ancient Biodiversity for Future Viticulture

Grapevine (Vitis vinifera) is one of the most widely cultivated plant species of agricultural interest, and is extensively appreciated for its fruits and the wines made from its fruits. Considering the high socio-economic impact of the wine sector all over the world, in recent years, there has been an increase in work aiming to investigate the biodiversity of grapevine germplasm available for breeding programs. Various studies have shed light on the genetic diversity characterizing the germplasm from the cradle of V. vinifera domestication in Georgia (South Caucasus). Georgian germplasm is placed in a distinct cluster from the European one and possesses a rich diversity for many different traits, including eno-carpological and phenological traits; resistance to pathogens, such as oomycetes and phytoplasmas; resistance to abiotic stresses, such as sunburn. The aim of this review is to assess the potential of Georgian cultivars as a source of useful traits for breeding programs. The unique genetic and phenotypic aspects of Georgian germplasm were unraveled, to better understand the diversity and quality of the genetic resources available to viticulturists, as valuable resources for the coming climate change scenario.

Oxidations in white grape (Vitis vinifera L.) skins: Comparison between ripening process and photooxidative sunburn symptoms

Oxidations in grape berries are gaining major interest as they affect grape characteristics and quality. Considering berries, Reactive Oxygen Species are involved in the responses to both ripening process and stresses, including photooxidative sunburn. Redox metabolism involves a multitude of chemical and enzymatic reactions. In this study, four white grape cultivars were examined for natural ripening and photooxidative sunburn effects (obtained in artificial conditions) on berry pigmentation, chemical composition and enzymatic activity. The measured parameters included reflectance spectra, pigmentation (including berry browning), content of photosynthetic pigments, organic acid profiles, antioxidant activity, concentrations of antioxidants (total phenolics, ascorbic acid and reduced glutathione), enzymatic activities (guaiacol peroxidases, ascorbate peroxidase and catalase). The effects of the treatment (natural ripening and artificial photooxidative sunburn) on each considered parameter are described in the paper. Photooxidative sunburn strongly affected the contents of antioxidants and chlorophylls, increased the browning index and modulated the enzymatic activities investigated. Samples clearly clustered depending on the oxidation status. Furthermore, the PCA highlighted the similarities and differences in the responses to oxidative stress during ripening and photooxidative sunburn. PCA produced five functions with eigenvalues higher than 1, representing 87.03% of the total variability. In particular, the scores of the function 1 discriminated the samples based on the oxidation status, while the function 2 separated the samples based on the sampling date, representing the physiological responses characteristic of ripening. Our work sheds light on this topic, and will allow a more conscious vineyard management, thus supporting the agricultural adaptation to climate changes.

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.

Implications of Aging Quality of Oak Shaving on Kyoho Wine Immersed with Residue of Cabernet Sauvignon

In order to study effect of oak sawdust on the quality of Kyoho wine immersed by fermented Cabernet Sauvignon residual, Kyoho wine aged without oak sawdust (KWO), including KWO1 and KWO2 according to immersed orders by fermented Cabernet Sauvignon residual, was taken as control to compare the effect of oak sawdust on quality of Kyoho wine (KO), including KO1 and KO2 according to aged orders by oak sawdust. During the 15 days of aging, physical and chemical indicators, such as chroma, tonality, and total phenol in wine were determined simultaneously by using a spectrophotometer, including tannin content by KMnO4 titration, once every 3 days. The results showed that the chromaticities of Kyoho wine were 3.21, 3.02, 4.46, and 3.71 for KO1, KO2, KWO1, and KWO2, respectively. Similarly, the hues were in turn 0.73, 0.68, 0.97, and 0.72, respectively. Tannin contents were 1601.5 mg/L, 1517.3 mg/L, 337.2 mg/L, and 115.6 mg/L; total phenol contents were 277.67 mg/L, 222.1 mg/L, 64 mg/L, and 79.8 mg/L. Therefore, the contents of tannin and total phenol from KO1 wine were all the highest values. The chroma and tone of the four types of wine showed an upward trend of “S.” The chromaticity and tone were the lowest for the KO2 wine and the highest for the KWO1 wine with the larger difference between KO2 and KWO1.