Aromatic Profiling of New Table Grape Varieties Using Gas Chromatography/Mass Spectrometry and Olfactometry.

The aim of this study is the aromatic characterization of new table grape varieties, namely Guzun (V. vinifera), Melona (V. vinifera), Cotton Candy (V. vinifera), IVC SA3 (V. labrusca), and IVC SB1 (V. labrusca). The qualitative and quantitative analysis of odorant molecules present in the berries allows for the definition of the aroma profile of the grape. This analysis benefits from the progress of analytical techniques and sensory methodologies. Gas chromatography/mass detection enable the efficient detection of the substances present and their concentrations. Through the coupling of gas chromatography with sensory detection (gas chromatography-olfactometry), it is possible to correlate the compounds detected by gas chromatography with olfactory stimuli, exploiting the human olfactory system. Aroma, a significant flavor component, is an important attribute of table grape that contributes to defining their quality. This characteristic is highly valued by consumers, and consequently, the market asks for table grapes with a particular or new aroma. Aromatic characterization is a crucial step in the study of the table grape varieties to evaluate their potential at the commercial level or, for instance, in breeding programs focusing on organoleptic properties.

Aroma precursors of Grignolino grapes (Vitis vinifera L.) and their modulation by vintage in a climate change scenario.

Current climatic conditions may cause significant changes in grapevine phenology and maturity dynamics linked often with changes to ecoclimatic indicators. The influence exerted by different meteorological conditions during four consecutive years on the aromatic potential of Grignolino grapes was investigated for the first time. The samples were collected from three vineyards characterized by different microclimatic conditions mainly related to the vineyard exposure and by a different age of the plants. Important differences as far as temperature and rainfall patterns are concerned during ripening were observed among the 4 years. Grape responses to abiotic stress, with particular emphasis on aromatic precursors, were evaluated using gas chromatography coupled to mass spectrometry. The results highlighted significant differences among the vintages for each vineyard in terms of the berry weight and the aromatic precursor concentration. For the grapes of the younger-vine vineyard, the content of aroma compounds showed a different variability among the vintages if compared to the old-vine vineyards. Optimal conditions in terms of temperature and rainfall during the green phase followed by a warm and dry post-veraison period until harvest favored all classes of compounds especially terpenoids mainly in the grapes of the old vines. High-temperature (>30°C) and low-rainfall pattern before veraison led to high benzenoid contents and increased differences among vineyards such as berry weight, whereas cooler conditions favored the terpenoid levels in grapes from southeast-oriented vineyards. In a hilly environment, lack of rainfall and high temperature that lately characterize the second part of berry development seem to favor the grape quality of Grignolino, a cultivar of medium-late ripening, by limiting the differences on bunch ripening, allowing a greater accumulation of secondary metabolites but maintaining at the same time an optimum balance sugar/acidity.

Direct quantification of sulfur dioxide in wine by Surface Enhanced Raman Spectroscopy.

A rapid Surface Enhanced Raman Spectroscopy (SERS) method to detect SO2 in wine is presented, exploiting the preferential binding of silver nanoparticles (AgNPs) with sulfur-containing species. This interaction promotes the agglomeration of the AgNPs and inducing the formation of SERS "hot spots" responsible for SO2 signals enhancement. For increasing SO2 concentrations from 0 to100 mg/l in wine simulant, SERS intensity showed an increasing trend, following a Langmuir absorption function (R2 = 0.94). Due to the wine matrix variability, a standard additions method was then employed for quantitative analysis in red and white wines. This method does not require the SO2 separation but only a matrix pre-cleaning by solid phase extraction. The limit of detection (LOD) was defined for each wine tested, ranging from 0.6 mg/l to 9.6 mg/l. The results obtained were validated by comparison with the International Organization of Vine and Wine method (OIV-MA-AS323-04A).

Key norisoprenoid compounds in wines from early-harvested grapes in view of climate change.

In view of climate change, the scheduling of an early harvest may be an agronomic option to limit wine alcohol, provided that a satisfactory content of secondary metabolites can be ensured in grapes. To better understand the link between grape ripening, seasonal trend and wine aroma, the aromatic expression of Barbera and Pinot Noir wines produced with early harvested grapes was assessed. Attention was focused on C13 norisoprenoids during both alcoholic fermentation and after three months of storage. At the end of fermentation, the highest ß-damascenone content was detected in wines obtained from less ripe grapes, the content subsequently increased significantly after three months of storage; however, the levels of ß-ionone decreased significantly during the same period. The reduction of wine alcohol as a result of harvesting earlier, especially for Barbera, was associated with optimal aromatic levels as well as good technological parameters.

Validation of a rapid conductimetric test for the measurement of wine tartaric stability.

This work was aimed at optimizing a rapid and reproducible conductivity test for the evaluation of wine tartaric stability, in order to improve the practices for the prevention of tartaric precipitations during bottle aging. The test consists in measuring the drop of conductivity in wines kept under stirring for a fixed time, at low temperature, after the addition of micronized potassium bitartrate crystals (KHT). An experimental design was planned to study three factors affecting the test: temperature, duration and dose of added potassium bitartrate. A standard protocol was defined to produce a micronized potassium bitartrate starting from available commercial products, since the dimensions of the crystals can affect the final conductivity values. After the choice of the best conditions the method was validated. Two different stability thresholds were defined for white wines and for red/rosé wines by comparing the results of the mini-contact test with those of the cold test.

Grape aroma precursors in cv. Nebbiolo as affected by vine microclimate.

The influence exerted by bunch microclimate on some C13-norisoprenoid precursors content was investigated for the first time in Nebbiolo grapes during ripening. Samples were collected, during two consecutive seasons, from two vineyards, which are characterized by different microclimatic conditions caused by vine vigour heterogeneity and different vineyard aspects. Enzymatic hydrolysis of the glycosides extracted from the grapes, and subsequent GC-MS determination of the aglycones, highlighted that the majority of norisoprenoid glycosides accumulated in Nebbiolo berries from pre-veraison until 3-4weeks post-veraison. Vineyard aspect and vine vigour affected the timing of the maximum concentration of norisoprenoid precursors and their subsequent decrease at harvest. Low light in the vigorous blocks penalized norisoprenoids peak concentration. In the south less vigorous blocks, a decline of total norisoprenoids content during the pre-harvest period was observed. This decline appeared mainly regulated by the temperature. Vintage and/or microclimatic conditions affected the final content of some important norisoprenoids.

Use of polyaspartate as inhibitor of tartaric precipitations in wines.

All additives used to stabilize wines against the precipitations of potassium bitartrate have some limits: metatartaric acid (MTA) is effective but very unstable, carboxymethylcellulose is stable and effective in white wines but affects color stability in red wines, mannoproteins have a variable effectiveness depending on wine composition. This work was aimed at testing the effect of new stabilizing products on tartaric precipitations, focusing on the use of Na and K polyaspartate salts (PASPs). The effectiveness of 4 different PASPs and 1 MTA added to red and white wines was compared using the mini-contact test and cold test. The dose effect and the stability of the products over time were also studied. The PASPs showed a similar stabilizing effect and a longer stability over time compared to MTA. PASPs can be considered interesting as additives for wine tartaric stabilization. Further work is in progress to better characterize their enological properties.

Influence of the matrix composition on the volatility and sensory perception of 4-ethylphenol and 4-ethylguaiacol in model wine solutions.

This study was aimed at investigating the influence of ethanol, wine polyphenols and yeast extract on the volatility of 4-ethylphenols in red wines. The use of solid-phase microextraction with short extraction times for the study of the headspace composition, revealed a strong influence of ethanol and polyphenols on reducing the volatility of 4-ethylphenols in a model wine. At the same time, the influence of ethanol and polyphenols on the perception of the "Brett character" (stable, manure, horse sweat and phenolic notes) due to 4-ethylphenols was evaluated by sensory analysis. Polyphenols and ethanol were found to have a significant influence on the olfactory perception of the tainted wines. On the contrary, a direct influence of yeast extract on the volatility of 4-ethylphenols was not observed, although some results suggested that the effectiveness of polyphenols in reducing the volatility of 4-ethylphenols could be limited by the presence of yeast proteins.