Patrizia Romano

Volatile metabolites produced in wine by mixed and sequential cultures of Hanseniaspora guilliermondii or Kloeckera apiculata and Saccharomyces cerevisiae

SummarySecondary products in wines obtained by pure, mixed and sequential cultures of Saccharomyces cerevisiae, Hanseniaspora guilliermondii or Kloeckera apiculata were studied. Consistent differences in the composition were determined in wines fermented by sequential cultures. When S. cerevisiae was added to musts partially fermented by apiculate yeasts, its metabolism was significantly affected. In particular it synthesized high amounts of n-propanol and metabolized high quantities of acetoin, produced by apiculate yeasts

Glycerol and other fermentation products of apiculate wine yeasts.

Ninety‐six strains of apiculate wine yeasts were studied for their ability to produce glycerol, acetaldehyde, ethyl acetate, sulphur dioxide and hydrogen sulphide in synthetic medium. Hanseniaspora guilliermondii produced smaller quantities of glycerol, acetaldehyde and hydrogen sulphide than Kloeckera apiculata, whereas the production of ethyl acetate and sulphur dioxide was found to be similar. Strains characterized by different capacities and properties were found for both species. The existence of apiculate strains differing in secondary compound production is of technological interest, as these yeasts constitute potential flavour producers. Selected strains of apiculate yeasts might favour an enhanced flavour formation and yield desirable characteristics to the final product.

Multiple strains of Saccharomyces cerevisiae on a single grape vine

M. POLSINELLI, P. ROMANO, G. SUZZI AND R. MORTIMER. 1996. On the basis of the levels of secondary product formation four different phenotypes were represented among the 28 strains of Saccharomyces cerevisiae isolated during the spontaneous fermentation of grape juice. The genetic analysis indicated that four different strains, representing each phenotypic class, were derived, one from the other, by mutation. The spontaneous fermentation of a Malvasia must was dominated by different strains of Saccharomyces cerevisiae at different stages of fermentation.

Potential use for Zygosaccharomyces species in winemaking

Some 29 strains of Zygosaccharomyces bailii and Zygosaccharomyces fermentati, isolated from grape juice, were examined for traits of oenological interest. The two species showed considerable differences in some of the characteristics studied. TheZygosacch. fermentati strains were found to possess a high fermentative vigour and to produce lower amounts of acetic acid in must, whereasZygosacch. bailii exhibited an interesting breakdown of malic acid (in same cases about 70%). A flocculation capability was found in all strains ofZygosacch. bailii. Both species produced low amounts of sulphur dioxide and hydrogen sulphide in must. The inherent characteristics found make the two species studied worth considering for different oenological uses.

Flocculent phenotypes in wine yeasts

The floc‐forming ability of highly flocculent wine yeasts isolated from musts and wines was tested for susceptibility to heat and proteinase treatments. Four phenotypes were discriminated by treatments with pronase, proteinase K, trypsin and chymotrypsin. The most common phenotype was irreversibly lost only upon treatment with pronase, whereas the floc‐forming ability was resistant to the action of proteinase K, trypsin and chymotrypsin. Another flocculent phenotype, represented by only one strain 6789, was resistant to the action of all proteolytic enzymes. The effect of high temperature on floc‐forming ability in the presence or absence of Ca2+ions resulted in all the possible combinations and did not aid further general discrimination of flocculent phenotypes in Saccharomyces cerevisiae strains from wine.

The flocculation of wine yeasts : biochemical and morphological characteristics in Zygosaccharomyces : flocculation in Zygosaccharomyces

The floc-forming ability of flocculent strains ofZygosaccharomyces bailii andZ fermentati, isolated from musts, was tested for susceptibility to proteinase and sugar treatments.Z. fermentati was found highly resistant to the proteolytic enzymes tested, whereasZ. baili was only trypsin-resistant.The inhibition of flocculation by sugars distinguished two types: inZ. fermentati flocculation was completely inhibited by mannose, inZ. bailli by various sugars.By SEM observation, the cell surface ofZygosaccharomyces revealed the presence of a column structure, resulting from fusion of vesicles present on the cell surface.

Cell surface hydrophobicity and flocculence in Saccharomyces cerevisiae wine yeasts

Abstract Cell surface hydrophobicity (CSH) of 18 flocculent strains of Saccharomyces cerevisiae was studied. The CSH was estimated by hydrophobic microsphere attachment assay (HMA) and by microbial adhesion to hydrocarbons assay (MATH). The MATH showed that all the different flocculent strains were hydrophobic, varying only in the degree of CSH. Conversely, some strains proved to be hydrophilic with HMA. Treatment of flocculent cells with proteolytic enzymes caused a dramatic decrease in the CSH in all the strains, changing their affinity from that for hydrocarbons to that for water. Such treatment did not abolish the flocculation ability of several strains. Reversible change of flocculation-dispersion by the addition of EDTA caused an increase in CSH. These data led to the conclusion that the CSH character is not always closely related to flocculation ability, demonstrating once more that flocculation is mediated by different mechanisms.

Microorganisms of Wine

A number of microorganisms can grow in grape must, depending on its composition: n n nfermentable sugars with the bulk consisting of glucose and fructose; n n nnitrogenous compounds, i.e. ammonia, amino acids and polypeptides; n n nminerals with the bulk consisting of potassium, calcium, magnesium, phosphates and sulphates; n n ngrowth factors, i.e. pantothenic acid, biotin, thiamine, pyridoxine and others.

Relationship between foaming and flocculence in Saccharomyces cerevisiae wine yeasts

Abstract The cell surface hydrophobicity (CSH) was studied in foaming and flocculent strains of Saccharomyces cerevisiae. Microbial adhesion to hydrocarbons showed a high CSH both in foaming and flocculent strains. When treated with EDTA the foaming strains responded differently from flocculent ones, with the CSH decreasing in the former and increasing in the latter. The treatment of cells with pronase, proteinase K, trypsin and chymotrypsin abolished the CSH activity in all the strains. When sugars (glucose, fructose, sucrose, galactose, mannose) were present, the strain hydrophobicity did not vary. The results indicate that foaming and flocculation are independent phenomena.