Correlation between cell lipid content, gene expression and fermentative behaviour of two Saccharomyces cerevisiae wine strains.

AIM: To verify a possible correlation between cell lipid composition, expression of key genes in lipid metabolism and fermentative behaviour of Saccharomyces cerevisiae wine strains. METHODS AND RESULTS: The fermentative abilities of two commercial wine strains of S. cerevisiae were tested under stressful conditions. Cell number, glucose and fructose concentrations, expression of ACS1, ACS2, ACC1, OLE1, ERG9, ERG10, ARE1 and ARE2 and lipid content were evaluated. The strain that failed to complete the fermentation had lower amounts of C16:1 and C16:0 fatty acids at the beginning of fermentation (0 h) and late logarithmic phase (72 h). While the amount of C18:1 in this strain was lower than that in the strain that completed the fermentation at 0 h, same levels were observed for both strains at 72 h. The sterol levels were generally higher in the strain that failed to complete the fermentation. Gene expression generally increased from the beginning of the fermentation to the late logarithmic phase in both strains. CONCLUSION: A positive correlation between good fermentative ability, elevated fatty acid content and ACC1 gene expression has been identified. SIGNIFICANCE AND IMPACT OF THE STUDY: The cell lipid content at the time of inoculum and expression of ACC1 gene of starter strains should be carefully considered in order to identify the possible stuck/sluggish fermentations.

Fenhexamid residues in grapes and wine.

The behaviour of the fungicide, fenhexamid, on grapes, and during wine-making, as well as its effect on the microflora of alcoholic and malolactic fermentation has been studied. After treatment, the residue on grapes decreased rapidly to one-third of the initial level after the first week, while it remained constant during the following two weeks. At harvest, in the wine obtained by vinification without skins, the fungicide residue decreased on average by 49%, while in the wine obtained by vinification with skins, the decrease was on average 62%. The presence of this fungicide on grapes and in the wine did not affect alcoholic and malolactic fermentation, nor did fermentation cause any degradation of the fungicide. A simple and rapid gas chromatograhic method (GC-NPD) for the determination of fenhexamid residues in grapes, must and wine is described.

A genetic study of natural flor strains of Saccharomyces cerevisiae isolated during biological ageing from Sardinian wines.

In this study, three flor strains of Saccharomyces cerevisiae were genetically characterized. They were isolated from biofilms on Sardinian sherry-like wines produced at family-run wineries where pure cultures of yeasts were not used. The study aimed to investigate the life cycle of these naturally-occurring flor strains, using a genetic procedure supplemented by analysis of subsequent meiotic generations. A semi-homothallic life cycle was found in three strains that could be helpful in a genetic improvement programme.

Fate of quinoxyfen residues in grapes, wine, and their processing products.

Quinoxyfen is a new fungicide that belongs to the family of the quinolines, recently introduced to control powdery mildew (Uncinula necator). In this paper the fate of quinoxyfen residues from vine to wine and in their processing products was studied. After the last of four applications at the recommended rate, 0.38 mg/kg of residue was found on the grapes, which is under the legal limit fixed in Italy (0.5 mg/kg). The degradation rate was according to a pseudo-first-order kinetics (r = 0.964) and the half-life was 7.24 days. Vinification was carried out with and without maceration. During the vinifications without maceration <50% of the residues passed from the grapes to the musts. Separation of the lees (8%) from the must by centrifugation caused no detectable residues in centrifuged must. At the end of fermentation with and without maceration no quinoxyfen residues were determinable in the wine. No effect on the alcoholic or malolactic fermentation was observed even in the presence of higher quinoxyfen concentrations than those found in the grapes at harvest time. During fermentation, the yeasts partially degraded the pesticides and completly adsorbed them. Bacteria, on the other hand, do not have any degradative effect on the pesticides. The raisins obtained by sun-drying did not contain any residues, whereas those obtained by oven-drying show the same amount of residues as in the fresh grapes. During the sun-drying process the fruit weight decreased by a factor of 4; the decrease in the oven-drying was equivalent. Samples of dregs and liquid lees, fortified with high levels of quinoxyfen. were double-distilled. The first dregs distillate, with an alcohol content of 32.1%, did not show any residues, whereas the first lees distillate, with an alcohol content of 34.5%, showed 7% of the initial residues. After the second lees distillation, the obtained product showed an alcoholic content of 81.2% and no residues of quinoxyfen (<0.01 mg/kg).

Pesticides in fermentative processes of wine.

The influence of six fungicides (azoxystrobin, cyprodinil, fludioxonil, mepanipyrim, pyrimethanil, and tetraconazole) on the fermentative activity of two yeasts (Saccharomyces cerevisiae and Kloeckeraapiculata) and two lactic bacteria (Leuconostoc oenos and Lactobacillus plantarum) was studied. The possibility of their being degraded by these yeasts and bacteria was also investigated. The presence of the pesticides did not affect alcoholic fermentation, not even with levels higher than those normally found in grapes in field experiments. On the contrary, their presence stimulated the yeast, especially K. apiculata, to produce more alcohol. The fermentative process did not affect the amount of pesticides either by degradation or by adsorption. During malolactic fermentation by Le. oenos, malic acid decreased slightly less (by approximately 15%) in the presence of all pesticides, except mepanipyrim. A lower effect ( approximately 5%) was found during the fermentative process with La. plantarum. The bacteria studied did not show a degradative effect on pesticides during malolactic fermentation.

Fungicidal activity of some o-nitrophenyl-hydrazones.

The antimycotic activity of 16 o-nitrophenylhydrazones against strains of Hansenula anomala, Saccharomyces cerevisiae, Candida parapsylosis, and Cryptococcus albidus was tested. All 16 compounds inhibited growth of the yeast strains. The inhibitory activity of the 4 methyl-derivatives substituted on the aromatic nucleus was particularly significant.

Antagonistic activity of Debaryomyces hansenii towards Clostridium tyrobutyricum and Cl. butyricum.

A study of the inhibitory action of Debaryomyces hansenii (31 strains) on Clostridium tyrobutyricum (5 strains) and Cl. butyricum (2 strains) on laboratory media showed that Deb. hansenii inhibited the growth of these organisms, and that this effect was due not only to competition for nutrients but also to the production of both extra- and intracellular antimicrobial metabolites. The inhibitory effect varied with strain and occurred whether the yeasts were grown aerobically or under reduced O2 tension.