Five 1999 varietal Douro table wines (Touriga Nacional, Touriga Francesa, Tinta Roriz, Tinto Cão, Tinta Amarela/Tinta Barroca mixed), one aguardente and five model Ports (aguardente fortified table wines) were quantified for 15 compounds by GC-MS using selected characteristic ions. Although aguardente constitutes around one fifth of the volume of Port, it was found to be the major contributor of numerous compounds including: ethyl hexanoate (81 to 90%); ethyl octanoate (94 to 98%); ethyl decanoate (98 to 99%); benzaldehyde (87 to 94%); a-terpineol (76 to 91%); linalool (58 to 91%); ethyl hydrocinnamate (100%). Aguardente volatiles make an essential contribution to young Port aroma, adding fruity, balsamic and spicy aroma complexity.
2,6,6-Trimethylcyclohex-2-ene-1,4-dione (TMCHD), a norisoprenoid with a sweet honey aroma descriptor, is reported for the first time as a minor constituent of single-varietal table and fortified wines from the demarcated Douro region. Olfactory gas chromatography (GC-O) of a volatile wine extract, previously isolated by preparative gas chromatography, indicated the presence of a zone containing an intense honey descriptor. The targeted odor compound was identified by GC-MS, GC-O, and Kovats index. Quantitative analysis using a selected characteristic ion (m/z 96) indicated that young Douro fortified wines from the 1997 vintage contained up to 4 microg/L TMCHD. The sweet honey sensory threshold limit for TMCHD in a model Port wine solution was found to be 25 microg/L. TMCHD is therefore only likely to contribute as a collective element to Port wine aroma. The wine volatile diacetyl was identified as a strong contributor to the sweet caramel aroma descriptor often associated with Port.
In winemaking, non-Saccharomyces yeast species contribute important organoleptic complexity. Current interest focuses on abundant and dominant strains characteristically present in the early phase of spontaneous alcoholic fermentations. Non-Saccharomyces species are particularly relevant in Port wine production such that the fermentation is prematurely stopped, after the metabolism of only one half of the available sugar, through fortification with aguardente. This work aimed to isolate, identify and characterize non-Saccharomyces species present in spontaneously fermenting Port. To accomplish these goals, yeasts were isolated from a selection of frozen must samples (2012–2016 harvests), using a pre-screening process choosing only the best candidates based on the organoleptic quality of the corresponding fortified wine. From five hundred non-Saccharomyces isolates, twelve species were identified. The three most abundant species, Hanseniaspora uvarum, Lachancea thermotolerans, and Metschnikowia pulcherrima, representing 89% of the isolates, exhibited particularly high diversity with high growth performance variability when exposed to typical stress conditions associated with common enological parameters. Less abundant species included Issatchenkia orientalis, Torulaspora delbrueckii, Hanseniaspora vineae, Hanseniaspora osmophila, Candida zemplinina, Rhodotorula mucilaginosa, Hanseniaspora guilliermondii, Issatchenkia occidentalis, and Zygosaccharomyces bisporus. This is the first study providing insights into the identification and characterization of non-Saccharomyces species responsible for spontaneous Port wine production.
1,3-Dimethoxybenzene was identified by GC-O, GC-MS and Kovats indices (polar Supelcowax, 1709; non-polar Rtx-5MS, 1158) as a new volatile component of port wine. Sensory evaluation described this compound as having a sweet medicinal odour with hazelnut, resinous and woody notes. Respective threshold limits in model wine and port wine were 21 and 47 mg l À1 . Quantitative analysis by GC-MS, using a selected characteristic ion (m/z 138), indicated that young port wines from the 1998 vintage contained up to 3 mg l À1 whereas ports from the 1999 vintage contained up to 20 mg l À1 .
The introduction of irrigation in vineyards of the Mediterranean basin is a matter of debate, in particular in those of the Douro Demarcated Region (DDR), due to the limited number of available studies. Here, we aimed to perform a robust analysis in three consecutive vintages (2018, 2019, and 2020) on the impact of deficit irrigation on the yield, berry quality traits, and metabolome of cv. ‘Touriga Nacional’. Results showed that in the peaks of extreme drought, irrigation at 30% crop evapotranspiration (ETc) (R30) was able to prevent a decay of up to 0.4 MPa of leaf predawn water potential (ΨPd), but irrigation at 70% ETc (R70) did not translate into additional protection against drought stress. Following three seasons of irrigation, the yield was significantly improved in vines irrigated at R30, whereas irrigation at R70 positively affected the yield only in the 2020 season. Berry quality traits at harvest were not significantly changed by irrigation, except for Total Soluble Solids (TSS) in 2018. A UPLC–MS-based targeted metabolomic analysis identified eight classes of compounds, amino acids, phenolic acids, stilbenoid DP1, stilbenoid DP2, flavonols, flavan-3-ols, di-OH- and tri-OH anthocyanins, and showed that anthocyanins and phenolic acids did not change significantly with irrigation. The present study showed that deficit irrigation partially mitigated the severe summer water deficit conditions in the DDR but did not significantly change key metabolites.
Three important monoterpene aroma releasing activities contained in an Aspergillus niger preparation were investigated for effects of pH, alcohol, Se, temperature and concentration of glucose. Application of the enzyme preparation during microvinification or wine maturation of a Portuguese white wine from "Trajadura" grapes, increased monoterpene content roughly 2-fold and 3-fold respectively . ABBREVIATIONS a-L-mf -a:L-arabinofuranosidase ; a-L-rhap -a-L-rhamnopyranosidase ; #%D-glup -& Dglucopyranosidase ; pnp -p-nitrophenyl.
Climate changes are speeding up the maturation of grapes in numerous areas of the world, including in the Mediterranean basin, but warmer temperatures often uncouple technical and phenolic maturity, resulting in unbalanced wines. We tested the efficacy of crop forcing (CF) in delaying the maturation of cv. ‘Touriga Nacional’ vines of the Douro Region, and their impacts on plant performance, berry quality attributes and metabolome were also evaluated. In two consecutive seasons (2019 and 2020), CF was conducted 15 (CF1) and 30 (CF2) days after fruit set by hedging growing shoots to five nodes and removing summer laterals, leaves and clusters. Results showed that while CF2 delayed ripening up to 51 days till first autumn rainfall, which compromised optimal sugar ripeness, CF1 delayed the technical maturation by one month, but both treatments severely impacted the production, mainly CF1, which reduced grapevine yield up to 90 %. The effect of CF in protecting vines against drought stress was not evident, judging by the values of leaf pre-dawn water potential measured along both seasons. CF1 and CF2 resulted in berries with lower pH and higher titratable acidity than controls, while total phenolics content increased by up to 48 % in 2020. A UPLC–MS-based targeted metabolomic analysis showed that CF increased the relative abundance of key metabolites like flavan-3-ols (i.e., catechin gallate increased by up to 661 %), trihydroxylated anthocyanins (i.e., delphinidin-3-O-glucoside increased by up to 656 % after CF2) and stilbenes (resveratrol increased by up to 700 % after CF2) with potential positive impacts in wine quality.
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