Comparison of Methoxypyrazine Content and Expression Pattern of O-Methyltransferase Genes in Grape Berries and Wines from Six Cultivars (Vitis vinifera L.) in the Eastern Foothill of the Helan Mountain

Timing of leaf removal modulates tannin composition and the level of anthocyanins and methoxypyrazines in Pinot noir grapes and wines

This study aimed to investigate the impact of leaf removal on concentrations of anthocyanin, tannin, and methoxypyrazines (MPs) in Pinot noir grapes and wines. Leaf removal after 7 days (LR7), 30 days (LR30), and 60 days (LR60) of flowering were compared with no leaf removal control (LRC). Grapes and resultant wines were analysed for tannin and aroma composition using liquid chromatography and two-dimensional gas chromatography-mass spectrometry. All leaf removal treatments increased anthocyanin concentration in grapes and reduced MP levels in grape stems compared to LRC, indicating the effectiveness of both early and late leaf removal. Leaf removal after 7 days and 30 days were more effective in enhancing colour density, polymeric pigments, and tannin concentration in wines. Higher grape skin tannin and anthocyanin concentrations, along with lower seed tannin concentration in berries, correlated with higher tannin concentrations in wines. LR7 showed significantly higher skin-originated tannin proportion than LRC, suggesting a useful tool to manage tannin extraction. Aroma composition of resultant wines was influenced by leaf removal, although these differences were not evident in the sensory evaluation.

Integrated Analysis of Transcriptome and Metabolome to Unveil Impact on Enhancing Grape Aroma Quality with Synthetic Auxin: Spotlight the Mediation of ABA in Crosstalk with Auxin

It is widely accepted that prevéraison application of naphthaleneacetic acid (NAA) can delay the ripening of grapes and improve their quality. However, how NAA impacts grape aroma compound concentrations remains unclear. This study incorporated the analyses of aroma metabolome, phytohormones, and transcriptome of Vitis vinifera L. cv. Cabernet Sauvignon grapes cultivated in continental arid/semiarid regions of western China. The analyses demonstrated that NAA application increased β-damascenone and 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) in the harvested grapes by delaying véraison and upregulating VvPSY1 and VvCCD4b expressions. Additionally, NAA treatment decreased 2-isobutyl-3-methoxypyrazine (IBMP) at the same phenological stage. Notably, abscisic acid (ABA) levels increased in NAA-treated grapes during véraison, which triggered further changes in norisoprenoid metabolisms. The ABA-responsive factor VvABF2 was potentially involved in VvPSY1 positive modulation, while the auxin response factor VvARF10 may play a role in VvCCD4b upregulation and VvOMT2 downregulation during NAA induction. VvARF10 possibly acts as a crosstalk node between the ABA and auxin signaling pathways following NAA treatment in regulating aroma biosynthesis.

Impact of Vine Water Status on 3-Alkyl-2-methoxypyrazine Content and Function Verification of VvOMT2/VvOMT3 Genes Associated with 3-Alkyl-2-methoxypyrazine Accumulation in "Marselan" Grape Berries (Vitis vinifera L.)

3-Alkyl-2-methoxypyrazines (MPs) could be considered as off-flavor for red wine if the concentration exceeds a certain threshold. It is unknown whether the vine water status has an influence on MP metabolism in grape berries and, therefore, in wines. This study aimed to evaluate the effect of vine water status on MP content and on the expression level of VvOMTs; moreover, the exact functions of VvOMT2/3 were investigated. In this study, the grapevines were subjected over two years (2020 and 2021) to different levels of water constraints and the treatments were (i) light water constraint (LW); (ii) moderate water constraint (MW); and (iii) severe water constraint (SW) in comparison with well-irrigated vines used as control (CK). The results showed that six MPs, including ETMP, MEMP, MOMP, SBMP, IPMP, and IBMP, were negatively and significantly affected by water constraints. Meanwhile, the levels of VvOMT1, VvOMT2, VvOMT3, and VvOMT4 were 0.17-fold, 0.13-fold, 0.35-fold, and 0.75-fold, respectively, at 40 DAA or 60 DAA under MW treatment relative to CK in 2020. In 2021, the trend was similar to that in 2020. When VvOMT2 and VvOMT3 genes were transiently overexpressed in grape berries and callus, both their expression level and protein level were induced; in addition, IPMP, SBMP, and IBMP contents were significantly increased. Moreover, heterologous expression of VvOMT3 in tomato led to IPMP, SBMP, and IBMP accumulation, whereas VvOMT2 could only promote the accumulation of IPMP. Altogether, moderate water constraint not only improved the quality of "Marselan" grape berries but also reduced the MP content per berry. This study showed for the first time, according to our knowledge, the effect of vine water constraint on the metabolism of MPs by way of allowing the reduction of the precursors of this aromatic compound, which could be perceived as an off-flavor impacting negatively wine aromatic profiles with notes of asparagus and green pepper.

Development of Tannins and Methoxypyrazines in Grape Skins, Seeds, and Stems of Two Pinot Noir Clones during Ripening

Two Pinot noir clones (AM10/5 and UCD5) were analyzed for tannin and methoxypyrazines (MPs) in different grape tissues during berry development using liquid chromatography and two-dimensional gas chromatography-mass spectrometry. On a per berry basis, skin tannins reached the maximum level about 2-3 weeks after véraison, seed tannins at around véraison, and stem tannins 4 weeks before véraison. Clone AM10/5 showed significantly higher levels of seed and stem tannins on a per berry basis at harvest. Tannin concentration and composition varied among the different tissues. On a per berry basis, stem tannin levels were comparable to skin tannins but were 3 to 4 times lower than seed tannins, while stem tannins had an intermediate galloylation (5-7%) between seed tannins (12-18%) and skin tannins (2%) and lower prodelphinidin (4-7%) than skin tannins (31-36%). The mean degree of polymerization of stem tannins was similar to seed tannins but lower than skin tannins. MPs, including 3-isopropyl-2-methoxypyrazine (IPMP), 3-s-isobutyl-2-methoxypyrazine (SBMP), and 3-isobutyl-2-methoxypyrazine (IBMP), showed significantly higher concentrations than their sensory thresholds in grape stems but not in skins. The MPs development in stems showed an increasing trend toward véraison and then a decreasing trend toward harvest. Compared to AM 10/5, UCD5 stems showed a higher level of MPs, especially significantly higher concentrations of IPMP and IBMP at harvest. The extraction of MPs from grape stems could contribute negative green and vegetative characters to Pinot noir wines.

Investigating the impact of pedoclimatic conditions on the oenological performance of two red cultivars grown throughout southern Italy

The cultivated grapevine, Vitis vinifera subsp. vinifera, possesses a rich biodiversity with numerous varieties. Each variety adapts differently to varying pedoclimatic conditions, which greatly influence the terroir expression of wine regions. These conditions impact vine growth, physiology, and berry composition, ultimately shaping the unique characteristics and typicity of the wines produced. Nowadays, the potential of the different adaptation capacities of grape varieties has not yet been thoroughly investigated. We addressed this issue by studying two grape varieties, Aglianico and Cabernet Sauvignon, in two different pedoclimatic conditions of Southern Italy. We evaluated and compared the effect of different pedoclimatic conditions on plant physiology, the microbial quality of grapes using Next-Generation Sequencing (NGS) technology, the expression trends of key genes in ripe berries and the concentration of phenolic compounds in grapes and wines by HPLC-MS, HPLC-DAD, NMR and spectrophotometric analyses. Metabolomic and microbiome data were integrated with quantitative gene expression analyses to examine varietal differences and plasticity of genes involved in important oenological pathways. The data collected showed that the phenotypic response of studied grapes in terms of vigor, production, and fruit quality is strongly influenced by the pedoclimatic conditions and, in particular, by soil physical properties. Furthermore, Aglianico grape variety was more influenced than the Cabernet Sauvignon by environmental conditions. In conclusion, the obtained findings not only reinforce the terroir concept and our comprehension of grape's ability to adapt to climate variations but can also have implications for the future usage of grape genetic resources.

Comparison of Chemical and Sensory Profiles between Cabernet Sauvignon and Marselan Dry Red Wines in China

The differences in chemical and sensory characteristics between Marselan and Cabernet Sauvignon in China were investigated with gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography-triple quadrupole mass spectrometry (HPLC-QqQ-MS/MS), combined with color parameters and sensory data. The paired t-test results showed that terpenoids, higher alcohols, and aliphatic lactones were significantly different according to the grape variety. Meanwhile, terpenoids could be considered as marker aroma compounds to distinguish Marselan wines from Cabernet Sauvignon, which could explain the distinct floral note in Marselan wines. The mean concentrations of the mv-vsol, mv-vgol, mv-vcol, mvC-vgol, mv-v(e)cat, mvC-v(e)cat, mv-di(e)cat, and cafA were higher in Marselan wines than Cabernet Sauvignon wines, and these compounds might confer Marselan wines with a deeper color, more red hue, and higher tannin quality. The phenolic profiles of Marselan and Cabernet Sauvignon wines were influenced by the winemaking process, mitigating the varietal differences. As for sensory evaluation, the intensities of herbaceous, oak, and astringency of Cabernet Sauvignon were more pronounced than Marselan, whereas the Marselan wines were characterized by a high color intensity and more redness, together with floral, sweet, and roasted sweet potato attributes, and tannin roughness.