Antonio Tirelli

Sulphur dioxide affects culturability and volatile phenol production by Brettanomyces/Dekkera bruxellensis

The effect of different sulphur dioxide concentrations on culturability and viability of seven strains of Brettanomyces bruxellensis was tested in a synthetic wine medium (SWM) and a different response to molecular SO(2) among strains was detected. Sulphur dioxide induced a viable but non culturable (VBNC) state in all the strains. The greater percentage of VBNC cells were identified for five strains at molecular SO(2) concentrations of 0.2mg/L and for two strains at the concentration of 0.4mg/L. Vinyl phenols were detected in media containing VBNC or not viable B. bruxellensis, suggesting that its spoilage metabolism could be maintained during wine storage. Overall, this study indicates that SO(2) is a chemical stressor inducing VBNC state in B. bruxellensis grown in synthetic wine medium. Further studies are needed to evaluate the effects of SO(2) on the metabolism of this yeast in wine spoilage.

Physiological and oenological traits of different Dekkera/Brettanomyces bruxellensis strains under wine‐model conditions

Contamination of wine by Dekkera/Brettanomyces bruxellensis is mostly due to the production of off-flavours identified as vinyl- and especially ethyl-phenols, but these yeasts can also produce several other spoiling metabolites, such as acetic acid and biogenic amines. Little information is available about the correlation between growth, viability and off-flavour and biogenic amine production. In the present work, five strains of Dekkera bruxellensis isolated from wine were analysed over 3 months in wine-like environment for growth, cell survival, carbon source utilization and production of volatile phenols and biogenic amines. Our data indicate that the wine spoilage potential of D. bruxellensis is strain dependent, being strictly associated with the ability to grow under oenological conditions. 4-Ethyl-phenol and 4-ethyl-guaiacol production ranged between 0 and 2.7 and 2 mg L(-1), respectively, depending on the growth conditions. Putrescine, cadaverine and spermidine were the biogenic amines found.

Genetic diversity and physiological traits of Brettanomyces bruxellensis strains isolated from Tuscan Sangiovese wines

Eighty four isolates of Brettanomyces bruxellensis, were collected during fermentation of Sangiovese grapes in several Tuscan wineries and characterized by restriction analysis of 5.8S-ITS and species-specific PCR. The isolates were subsequently analysed, at strain level, by the combined use of the RAPD-PCR assay with primer OPA-02 and the mtDNA restriction analysis with the HinfI endonuclease. This approach showed a high degree of polymorphism and allowed to identify seven haplotypes, one of them being the most represented and widely distributed (72 isolates, 85.7%). Physiological traits of the yeasts were investigated under a wine model condition. Haplotypes clustered into two groups according to their growth rates and kinetics of production of 4-ethylphenol and 4-ethylguaiacol. Hexylamine was the biogenic amine most produced (up to 3.92 mg l(-1)), followed by putrescine and phenylethylamine. Formation of octapamine was detected by some haplotypes, for the first time.

Determination of Reduced Cysteine in Oenological Cell Wall Fractions of Saccharomyces cerevisiae

Compounds containing cysteine residues, such as glutathione, can affect the redox potential of must and wine by reduction of o-quinones and hydrogen peroxide. The oenological yeast cell wall fractions contain cysteine residues in their protein structure, and they could affect both oxidative and odor properties of wine. An analytical approach based on the derivatization of cysteinyl residues with p-benzoquinone followed by reversed-phase high-performance liquid chromatography separation was developed to quantify glutathione and free and protein cysteine in 16 Saccharomyces cerevisiae strains and 12 commercial samples of yeast mannoproteins, hulls, and lysates. The chemical modifications induced by the Maillard reaction following the industrial preparation of such fractions were evaluated as well. Lysates showed the highest protein cysteine content and high contents of glutathione and free cysteine. Mannoproteins showed an intense Maillard reaction (furosine >60 mg/100 g protein), and most of the samples were able to bind thiol compounds with a potentially detrimental effect toward the thiol-related odors in wine.

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.

Survey on indigenous Oenococcus oeni strains isolated from red wines of Valtellina, a cold climate wine-growing Italian area.

Spontaneous MLF in high acidity wines produced in cool-climate regions remains problematic though indispensable for the development of sensory characteristics. Genetic aspects and phenotypic traits of thirty-six Oenococcus oeni strains, most of them isolated from Valtellina wines over three consecutive years, were investigated. Molecular typing achieved by RAPD PCR and PFGE analyses allowed 27 different genotypes to be discriminated, whereas from the comparison of results arising by physiological tests (sugar fermentation, alcohol resistance, growth at low temperatures, biogenic ammines production) 28 different phenotypic profiles were obtained. Particularly, 69% of Valtellina isolates were able to develop at 5 degrees C in cultural broth. Micro-vinification experiments allowed the selection of strains with potential oenological performances and an interesting capability to grow in cold conditions was confirmed. Some O. oeni strains formed phenylethylamine (up to 47 mg/L) and tyramine (up to 36 mg/L) both in cultural broth and wine.

Phenylacetaldehyde by acetic acid bacteria oxidation of 2-phenylethanol

SummaryThis paper reports the production of 2-phenylacetaldehyde from 2-phenylethanol by acetic bacteria. Several strains of acetic bacteria were investigated and three were found to be effective for this bioconversion. Different conditions (different C source for the microorganisms, pH, substrate concentration, cell immobilization) were tested with yields ranging from 30 to 52.6%.

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.

Brettanomyces bruxellensis yeasts: impact on wine and winemaking

Yeasts belonging to the Brettanomyces/Dekkera genus are non-conventional yeasts, which affect winemaking by causing wine spoilage all over the world. This mini-review focuses on recent results concerning the presence of Brettanomyces bruxellensis throughout the wine processing chain. Here, culture-dependent and independent methods to detect this yeast on grapes and at the very early stage of wine production are encompassed. Chemical, physical and biological tools, devised for the prevention and control of such a detrimental species during winemaking are also presented. Finally, the mini-review identifies future research areas relevant to the improvement of wine safety and sensory profiles.