"Pecorino di Filiano" cheese as a selective habitat for the yeast species, Debaryomyces hansenii.

The composition of yeast microflora in artisanal "Pecorino di Filiano" cheese, a typical product of the Basilicata region of Southern Italy, was studied during ripening. The isolates were identified by restriction analysis of the 18S rDNA amplified region with the combined use of Hinf I and Cfo I enzymes. The majority of the isolates were identified as Debaryomyces hansenii, whereas two yeasts were identified as Kluyveromyces lactis and one as Dekkera anomala. To evaluate natural biodiversity, D. hansenii "Pecorino di Filiano" isolates were submitted to genetic and technological characterization. RAPD-PCR analysis with P80 (5CGCGTGCCCA3) primer revealed significant polymorphism among D. hansenii isolates. About 30% of the isolates showed single molecular profiles, whereas the other D. hansenii yeasts were separated into three main patterns, differing for both the ripening time and the isolation source. Furthermore, the yeasts showed significant variability in their, "proteolytic activity". This work demonstrated the high predominance of D. hansenii among the yeast population of "Pecorino di Filiano" cheese, probably in consequence of the traditional salting process, which was selected for this salt tolerant species. This preliminary study allowed us to isolate autochthonous D. hansenii yeasts potentially useful as starters for the production of this artisanal cheese.

Molecular and technological approaches to evaluate strain biodiversity in Hanseniaspora uvarum of wine origin.

AIMS: The characterization by molecular and physiological methods of wild apiculate strains, isolated from 'Aglianico del Vulture' grape must. METHODS AND RESULTS: The restriction analysis of 18S rDNA allowed the identification of strains at the species level, which were predominantly Hanseniaspora uvarum. The RAPD analysis and the evaluation of technological traits, such as the metabolic and enzymatic activities, were useful to evaluate the polymorphism of this species. CONCLUSIONS: The RAPD analysis clustered the wild H. uvarum strains in four main genetic groups and a very high phenotypic variability confirmed this genetic polymorphism. The technological variables, which determined the strain biodiversity differed significantly, demonstrating that these technological traits are strain dependent. A certain correlation was found between the strain behaviour and its isolation zone, indicating the influence of the environment on the genetic patrimony of the population. SIGNIFICANCE AND IMPACT OF THE STUDY: The genetic and technological biodiversity recorded among H. uvarum wild strains represents the basis for organizing a collection of apiculate strains exhibiting oenological characteristics at different levels, such as high/low production of secondary compounds, and, therefore, potentially useful for a selection programme.

Yeasts from Water Buffalo Mozzarella, a traditional cheese of the Mediterranean area.

Countries of the Mediterranean area are characterized by production of artisanal cheeses, obtained from goat, sheep, cow and buffalo raw milk. The numbers and species of yeasts in the different cheeses are variable, but some species are more frequently detected than others. Kluyveromyces marxianus, K. lactis with their anamorph, Candida kefir, Debaryomyces hansenii and C. famata, C. colliculosa and C. catenulata are dominant species in several cheeses. However, Saccharomyces cerevisiae is often detected in pasta filata cheeses, such as Water Buffalo Mozzarella (WBM) or Cacio Cavallo Podolico. Recently, a comprehensive study of yeasts isolated from Mozzarella cheese produced in Basilicata (Southern Italy) has been carried out. The study has focused on lactose and/or galactose fermenting species (Kluyveromyces and Saccharomyces) to evaluate their role on the functional and sensory properties of the product. End products in milk were evaluated and the biodiversity in terms of production of sulphur dioxide, higher alcohols, ethyl acetate, and acetaldehyde was studied. In particular, S. cerevisiae strains from Water Buffalo Mozzarella cheese, compared to strains isolated from different habitats, such as wine, exhibited considerable difference in the production of some volatile compounds. The diversity observed could be related to the particular microhabitat of S. cerevisiae occurring in whey cheese of water buffalo milk.

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.

Biometric Study of Acetoin Production in Hanseniaspora guilliermondii and Kloeckera apiculata.

Gas chromatographic analysis by direct injection of samples yielded quantitative data on acetoin content. Ninety-six strains of Hanseniaspora guilliermondii and Kloeckera apiculata were investigated for the ability to produce acetoin in synthetic medium and in must. High-level production of acetoin was found to be a characteristic of both species. In synthetic medium, the two species were not significantly different with respect to sugar utilization and ethanol or acetoin production. In grape must, the two species were significantly different (P = 0.001) in acetoin production and K. apiculata exhibited a significantly negative correlation between acetoin production and either sugar consumption or ethanol production. Use of selected apiculate yeasts in mixed cultures with Saccharomyces cerevisiae seems promising for optimization of wine bouquet.