Mario Gabrielli

Yeast contribution to melatonin, melatonin isomers and tryptophan ethyl ester during alcoholic fermentation of grape musts

Melatonin (MEL) has been found in some medicinal and food plants, including grapevine, a commodity of particular interest for the production of wine, a beverage of economic relevance. It has also been suggested that MEL in wine may, at least in part, contribute to the health‐promoting properties attributed to this beverage and, possibly, to other traditional Mediterranean foodstuffs. After a preliminary screening of 9 yeast strains in laboratory medium, three selected strains (Saccharomyces cerevisiae EC1118, Torulaspora delbrueckii CBS1146T and Zygosaccharomyces bailii ATCC36947T) were inoculated in experimental musts obtained from 2 white (Moscato and Chardonnay) and 2 red (Croatina and Merlot) grape varieties. The production of MEL, melatonin isomers (MIs) and tryptophan ethyl ester (TEE) was monitored during the alcoholic fermentation. The screening showed that the three investigated strains produced the highest concentrations of MEL and two MIs in optimal growth conditions. However, MEL and MIs were not produced in oenological conditions, but the three strains synthesized high concentrations of a new MI and TEE in musts.

Determination of sotolon content in South African white wines by two novel HPLC–UV and UPLC–MS methods

Sotolon has been reported to play an important role in the atypical ageing and aroma character of many wines. A number of analytical techniques for sotolon analysis in wine have been reported, but these often require extensive sample preparation. In this work we report a HPLC-UV method and a novel UPLC-MS method to determine sotolon concentrations in white wines with little sample preparation applied for the first time for the evaluation of sotolon levels in South African wines. The validation showed that the instrumental methods had good accuracy, repeatability and linearity, but the UPLC-MS method proved more sensitive. For both methods, quantification limits were lower than the sotolon odour threshold in wine (10μg/L), 0.86μg/L and 0.013μg/L, for HPLC-UV and UPLC-MS methods, respectively. Sotolon levels in 65 South African white wines were often found to be lower than the reported odour threshold, with the highest concentration being 9.11μg/L. However, for low levels (<1μg/L), unknown interferences in certain wines led to sotolon not being quantified with the HPLC-UV method, which made the UPLC-MS method more suitable.

UHPLC Quantification of Sotolon in White Wine

Sotolon (4,5-dimethyl-3-hydroxy-2,5-dihydrofuran-2-one) is a volatile compound involved in the atypical aging of dry white wine, causing an irreversible defect when it exceeds 7-8 μg L(-1), and it might be adopted as a chemical marker of oxidative aging. An easier and sensitive ultrahigh-pressure liquid chromatography method for its determination in white wine is reported. The sample preparation is based on the liquid/liquid extraction by dichloromethane and the purification by solid phase extraction of the redissolved dry sample. This method showed good linearity and intermediate repeatability (<0.7 μg L(-1)), high recovery (>89.5%), and low detection limit (0.029 μg L(-1)). This method was usefully applied to 30 Italian sparkling and still white wine samples, where sotolon was not detected in most of them and exceeded the perception threshold only in one sparkling wine (13 μg L(-1)). The proposed method could be used to further investigate the aging/storage conditions and the chemical-physical parameters affecting its formation in wine.

Thiol precursors in Catarratto Bianco Comune and Grillo grapes and effect of clarification conditions on the release of varietal thiols in wine

Background and Aims Varietal thiols characterise the typical aroma of several white wines, such as Sauvignon Blanc. Their presence and sensory perception were suggested in two Sicilian grape cultivars, Catarratto Bianco Comune (CBC) and Grillo, though it has not been analytically proven. Methods and Results Varietal thiol precursors and free varietal thiols were assessed in CBC and Grillo grapes, musts and wines by ultra-performance liquid chromatography/electrospray ionisation high-resolution MS. The isobaric compounds including S-3-(hexanal)-glutathione and S-3-(4-mercapto-4-methylpentan-2-one)-glutathione (GSH-4MMP) were distinguished by comparing their accurate masses and high-resolution-MS/MS spectra with those of their synthetic standards. S-3-(Hexanal)-glutathione, S-3-(hexan-1-ol)-glutathione and S-3-(hexan-1-ol)-cysteine were found in grape, must and wine, whereas GSH-4MMP and its hydrolysed forms were not found. Their concentration decreased during winemaking, mostly after grape pressing. We compared the effect of clarification conditions based on the exposure of must to either air or CO2 on the concentration of thiol precursors and free thiols in wine; however, negligible differences were observed. The concentration of free thiols in the wines was found to be in the range 400–1100 ng/L and they were unaffected by the two clarification conditions tested. Conclusions The isobaric S-3-(hexanal)-glutathione and GSH-4MMP were clearly distinguished for the first time by ultra-performance liquid chromatography/high-resolution MS through their retention times and MS spectra. These varietal thiols were revealed in CBC and Grillo wines for the first time. The air-free and air-exposed clarification treatments had little effect on the concentration of the varietal thiols. Significance of the Study This study highlights the major impact of the varietal thiols (mainly 3-mercapto-hexan-1-ol and its acetate form) on the sensory properties of CBC and Grillo wines.

Characterisation of vernaccia Nera (Vitis vinifera L.) grapes and wine

Vernaccia Nera (VN) is a minor Italian red grape cultivar whose oenological properties have not been investigated, yet. The traditional winemaking procedures with VN may include grape drying and even triple sequential fermentations, but a rational vinification approach should be based on the grape composition. Since a comprehensive characterization of VN grape is still missing, the ripening of VN grape was monitored by evaluating flavour compounds, proanthocyanidins and anthocyanins. The grapes were used to produce red wine whose chemical composition and sensory properties were assessed. Ripe VN grape contained high amounts of extractable anthocyanins (875 mg/kg). The most abundant anthocyanin was malvidin (56.6%) and high relative amounts of cumarate forms (11.3%) were also found. The grape skin showed high concentration of proanthocyanidins (2 g/kg) whose degree of polymerization was low (10.3). Epigallocatechin accounted up to 39% of the flavan-3-ol units in the skin. Flavour compounds in grape included glycosylated norisoprenoids (mainly 3-oxo-?-ionol and vomifoliolo) and benzenoids. The VN red wine showed high amount of anthocyanins, but the level of proanthocyanidins (0.93 g/L) was lower than expected. The spicy flavors were the notes mostly recognized with the sensory. Our data highlight VN grape is suitable for the production of ready-to-drink or shortly aged red wine due to the high acidity and low astringency.