Some clues about the changes in wine aroma composition associated to the maturation of “neutral” grapes

Influences of Cluster Thinning on Fatty Acids and Green Leaf Volatiles in the Production of Cabernet Sauvignon Grapes and Wines in the Northwest of China

Cluster thinning has been widely applied in yield management and its effect on green leaf volatiles (GLVs) in wines has seldom been studied. GLVs are important flavor compositions for grapes and wines. This work aimed to investigate the impact of cluster thinning on these volatiles and their precursors in grapes and wines. Severe cluster thinning (CT1) and medium cluster thinning (CT2) were performed on Cabernet Sauvignon (Vitis vinifera L.) vines in two sites (G-farm and Y-farm) from Xinjiang province in the Northwest of China. The impact of cluster thinning treatments on the accumulation of GLVs and their precursors, long chain fatty acids (LCFAs) of grape berries and C6 volatiles, in resulting wines was investigated. Multivariate analysis showed that cluster thinning treatments induced significant changes in fruit and wine composition in both farms. In Y-farm, medium cluster thinning (CT2) significantly increased the average cluster weight of harvested berries. Additionally, both cluster thinning treatments (CT1 and CT2) increased fatty acids in harvested berries and CT2 led to an increase in C6 esters and a decrease in C6 alcohols in the wines of Y-farm under the warmer and drier 2012 vintage. However, the effect of cluster thinning was likely negative in G-farm due to its wetter soil and excessive organic matter. The treatments may be applicable for local grape growers to improve viticultural practices for the more balanced vegetative and reproductive growth of Cabernet Sauvignon grapevines. This work also provided further knowledge on the regulation of fatty acids and the derived C6 volatiles through the lipoxygenase (LOX) pathway.

Evolution of Seed-Soluble and Insoluble Tannins during Grape Berry Maturation

Condensed tannins (CT) in wine are derived from the seeds and skins of grapes, and their composition and content contribute to the bitterness/astringency characteristics and ageing potential of the wine. Global warming has accelerated the ripening process of grape berries, making them out of sync with seed ripening. To understand the influence of berry ripening on the seed CT composition and content, we analyzed the changes in the soluble and insoluble CT in the seeds of 'Cabernet Sauvignon' grapes from two vineyards over two years. The results showed that the seed-soluble CT presented a slight downward trend in fluctuation during grape berry development, while the insoluble CT increased continuously before the véraison and remained at a high level afterwards. Relatively speaking, a lower sugar increment in developing grape berries favored the conversion of seed CT towards a higher degree of polymerization. The terminal unit of soluble CT was dominated by epigallocatechin gallate, the content of which decreased as the seeds matured. It is suggested that the seeds should be fully matured to reduce this bitter component in tannins. This study provides a reference for us to control the grape ripening process and produce high-quality grapes for wine making.

A Sustainable Approach Based on the Use of Unripe Grape Frozen Musts to Modulate Wine Characteristics as a Proof of Concept

Aiming to develop a sustainable methodology for must acidity correction in winemaking, particularly needed in warm regions, the present study intends to fulfill the circular economy values. Antão Vaz white wines were produced using two different strategies for must acidity correction: (i) the addition of a mixture of organic acids (Mix*) commonly used in winemaking; and (ii) the addition of previously produced unripe grape must (UM*) from the same grape variety. In addition, a testimonial (T*) sample was produced with no acidity correction. For all wines produced, oenological parameters were determined, and both amino acid (AA) content and volatile composition were evaluated. A higher AA content was found in the Antão Vaz T* wine, followed by UM* wines. The volatile profile was also affected, and LDA demonstrates a clear separation of wines with different acidity corrections. Results obtained indicate that unripe grape musts—a vital waste product containing several compounds with important biological activity—can be used to increase musts acidity without a negative impact on wine characteristics. Furthermore, this work also shows that the use of unripe must may be a valuable tool for reducing the alcoholic content of wines.

Effects of Methyl Jasmonate and Nano-Methyl Jasmonate Treatments on Monastrell Wine Volatile Composition

The application of methyl jasmonate (MeJ) as an elicitor to enhance secondary metabolites in grapes and wines has been studied, but there is little information about its use in conjunction with nanotechnology and no information about its effects on wine volatile compounds. This led us to study the impact of nanoparticles doped with MeJ (Nano-MeJ, 1mM MeJ) on the volatile composition of Monastrell wines over three seasons, compared with the application of MeJ in a conventional way (10 mM MeJ). The results showed how both treatments enhanced fruity esters in wines regardless of the vintage year, although the increase was more evident when grapes were less ripe. These treatments also achieved these results in 2019 in the cases of 1-propanol, ß-phenyl-ethanol, and methionol, in 2020 in the cases of hexanol and methionol, and in 2021, but only in the case of hexanol. On the other hand, MeJ treatment also increased the terpene fraction, whereas Nano-MeJ, at the applied concentration, did not increase it in any of the seasons. In summary, although not all families of volatile compounds were increased by Nano-MeJ, the Nano-MeJ treatment generally increased the volatile composition to an extent similar to that obtained with MeJ used in a conventional way, but at a 10 times lower dose. Therefore, the use of nanotechnology could be a good option for improving the quality of wines from an aromatic point of view, while reducing the necessary dosage of agrochemicals, in line with more sustainable agricultural practices.

Maturation of Moristel in Different Vineyards: Amino Acid and Aroma Composition of Mistelles and Wines with Particular Emphasis in Strecker Aldehydes

The aim of this article was to assess the influence of the harvest date on the composition of amino acids and derived aromatic compounds in grape-mistelle and wine of the Moristel variety, in different vineyards. Two vineyards were sampled in 2016 and another one in 2017. At each sampling point, grapes were collected, destemmed, crushed and divided into four aliquots. The first three were fermented, and the latter was treated with ethanol, to produce 1-week macerates containing 15% ethanol (v/v)-mistelles. Overall, 10 mistelles and 33 wines were produced. Amino acids, Strecker aldehydes and aroma compounds were analysed. Amino acid profiles are characteristic of the vineyard and level of ripeness, converging with maturation. In fermentation, major amino acids, except proline, are consumed at a relatively fixed and specific tax, while consumption of 13 amino acids is determined by the ratios of alanine, glutamic acid, serine and threonine, with γ-aminobutyric acid. After fermentation, amino acid precursors to Strecker aldehydes are maxima in unripe and overripe samples, while Strecker aldehydes are maxima in unripe wines. No direct correlations between precursor amino acids in mistelle and aromatic compounds in wine have been found. Nevertheless, must amino acid profiles could determine wine aroma composition.

Influence of Berry Ripening Stages over Phenolics and Volatile Compounds in Aged Aglianico Wine

The harvest time of grapes is a major determinant of berry composition and of the wine quality, and it is usually established through empirical testing of main biochemical parameters of the berry. In this work, we studied how the ripening stage of Aglianico grapes modulates key secondary metabolites of wines, phenolics and volatile compounds. Specifically, we analyzed and compared four berry ripening stages corresponding to total soluble solids of 18, 20, 22, and 25 °Brix and related aged wines. Wine color intensity, anthocyanins level and total trans-resveratrol (free + glycosidic form) increased with grape maturity degree. Wines obtained from late-harvested grapes significantly differed from the others for a higher content of aliphatic alcohols, esters, acetates, α-terpineol and benzyl alcohol. The content of glycosidic terpene compounds, such as nerol, geraniol and α-terpineol, was higher in wines obtained with grapes harvested at 25 °Brix compared to the earlier harvests. Our work indicated that the maturity of the grape is a determining factor in phenolic and volatile compounds of red Aglianico wines. Moreover, extending grape ripening to a sugar concentration higher than 22 °Brix improves the biochemical profile of aged wine in terms of aroma compounds and of phytochemicals with known health-related benefits.

Insights on the role of acetaldehyde and other aldehydes in the odour and tactile nasal perception of red wine

Wine models with or without a dearomatised and lyophilized red wine extract containing a young red aroma base (control) plus one vector with one or several aroma compounds (unsaturated-aldehydes, saturated-aldehydes, benzaldehyde, isoamyl-alcohol, methoxypyrazines and (Z)-1,5-octadien-3-one) were prepared. Models were spiked with increasing amounts of acetaldehyde whose headspace concentrations were controlled. Odour and nasal chemesthesic properties were assessed by a trained sensory panel. Results confirm the contribution of the different players, notably isoamyl-alcohol, (Z)-1,5-octadien-3-one, benzaldehyde and methoxypyrazines, to wine aroma and tactile nasal characteristics and demonstrate that acetaldehyde levels play an outstanding role in their modulation. At low levels, it can play positive roles in some specific aromatic contexts, while at higher levels, enhance the negative effects associated to the generic presence of other aldehydes (saturated, unsaturated and Strecker aldehydes) by enhancing "green vegetable" notes and "itching" character and the "burning" effects linked to high levels of isoamyl alcohol.

Revealing the yeast modulation potential on amino acid composition and volatile profile of Arinto white wines by a combined chromatographic-based approach

The importance of yeasts in aroma production during wine fermentation is a significant concern for obtaining a wine that appraises a broad number of consumers. For wine producers, wine aroma modulation is an essential issue where the yeasts used during the winemaking process represents a feasible way to improve the complexity and enhance wines specific characteristics. During the fermentation process of wines, yeasts convert grapes sugars into alcohol, carbon dioxide and a large number of secondary metabolites, depending on yeast metabolism, affecting the wine composition, namely its aroma and amino acids (AAs) composition. So, the present work aims to study the effect of different Saccharomyces-type yeasts on the AAs composition and volatile profile of Arinto white wines. To pursue this goal, four white wines from Arinto grapes were fermented with three different commercial yeasts (Saccharomyces bayanus EC1118, Saccharomyces cerevisiae CY3079, Saccharomyces bayanus QA23) and one Native yeast. Arinto wines AAs composition was quantified by HPLC-DAD, after a derivatization step to obtain the aminoenone derivatives. The volatile content of Arinto wines was determined by GC/MS, after an HS-SPME extraction. Results showed significant differences among the AAs content and volatile profile in the Arinto wines. The higher AAs content was found in the Arinto wines fermented with the CY3079 yeast (470.74 mg•L^-1), and the lowest content of AAs in the Arinto wines fermented with EC1118 yeast (343.06 mg•L^-1). Native yeast results in wines with a volatile profile richer in esters compared to the other sample wines. Principal component analysis (PCA) obtained with combined data of AAs and volatile compounds, after normalization, for each Arinto wine samples, shows a clear separation of wines fermented with Native and CY3079 yeasts in relation to QA23 and EC1118 fermented wines . The first and second principal components are responsible for 44.40% and 32.20%, respectively, of the system's variance, which clearly showed a differentiation among wines.

Extended Harvest Date Alter Flavonoid Composition and Chromatic Characteristics of Plavac Mali (Vitis vinifera L.) Grape Berries

This study delivers a comprehensive flavonoid fingerprint profile, physiochemical and external color characterization of Plavac Mali grapes through four harvest dates at two distinct vineyards (Split and Zadar) in the Eastern Adriatic region. The experimental harvest lasted 56 days, at total soluble solids content from 18.4 to 22.4°Brix in Split and 16.8 to 20.4°Brix in Zadar. Patterns of 27 skin and seed flavonoid compounds at each location indicate unique flavonoid composition of berries at each harvest date. Extended harvest increased six compounds in skin with maximum values of main anthocyanin malvidin-3-O-glucoside in H3 (4406.6 and 6389.5 mg kg⁻¹, Split and Zadar, respectively) followed by a decrease in October. Peak values of seed and skin catechins and galloylated flavan-3-ol subunits are seen in H1 and H2 at Split, while constantly high values are reported in the case of Zadar, with an incoherent pattern of those in skin extracts. Minimal values of epigallocatechin were detected with an extended harvest date at both locations. Berries of extended harvest dates underwent colorimetric improvements, trough decrease in L*, a*, b* and C characteristics and increase in skin color index for red grapes CIRG. The extended harvest date promotes flavonoid composition, and improves the quality of Plavac Mali grape berries.

Grape terpenoids: flavor importance, genetic regulation, and future potential

Terpenes significantly affect the flavor and quality of grapes and wine. This review summarizes recent research on terpenoids with regard to grape wine. Although, the grapevine terpene synthase gene family is the largest identified, genetic modifications involving terpenes to improve wine flavor have received little attention. Key enzyme modulation alters metabolite production. Over the last decade, the heterologous manipulation of grape glycosidase has been used to alter terpenoids, and cytochrome P450s may affect terpene synthesis. Metabolic and genetic engineering can further modify terpenoid metabolism, while using transgenic grapevines (trait transfer to the plant) could yield more flavorful wine. We also discuss traits involved in wine aroma quality, and the strategies that can be used to improve grapevine breeding technology.