Characterization of yeasts involved in the ripening of Pecorino Crotonese cheese.

The aims of this work were to identify and characterize for some important technological properties the yeast species present throughout the ripening process of Pecorino Crotonese, a traditional cheese produced in a well defined area of Southern Italy. In particular, the strain technological properties considered include fermentation/assimilation of galactose and lactose, assimilation of lactate and citrate in the presence of different NaCl concentrations, hydrolysis of butter fat, skim milk, gelatine and casein, production of brown pigments in cheese agar and ability to produce biogenic amines. High yeast levels were recorded in cheese samples already after 5 h of brining (about 5 log cfu/g) and these concentration remained constant during ripening. The yeast isolates belonged to restrict number of yeast species. While Kluyveromyces lactis and Saccharomyces cerevisiae were isolated prevalently in the first stages of Pecorino Crotonese production, Yarrowia lipolytica and Debaryomyces hansenii dominated during the later stages of maturation. Otherwise, the latter two were very NaCl resistant species. In fact, D. hansenii strains conserved the ability to assimilate lactose and galactose in the presence of 10% NaCl, while almost all the strains of Y. lipolytica isolated assimilated citrate and lactate up to 7.5% NaCl. Y. lipolytica isolates evidenced also the highest proteolytic and lipolytic activities and the capability to catabolize tyrosine producing brown pigment. In addition they resulted in the highest aminobiogenic potential decarboxylating ornithine, phenylalanine, tyrosine and lysine. However, they were not able to produce histamine, biogenic amine produced by three strains of D. hansenii.

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.

Randomly amplified polymorphic DNA (RAPD) PCR for the identification of yeasts isolated from dairy products.

In the present work randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) with primers M13 and RF2 was applied to the identification at species level of yeast strains isolated from cheeses. RAPD-PCR analysis of the type strains of different yeast species gave distinctive band profiles that allowed a clear differentiation of all the considered species. Forty-two of the 48 dairy associated yeasts were clearly assigned to the species Saccharomyces cerevisiae, Kluyveromyces marxianus (anamorph Candida kefyr), Kluyveromyces lactis (anamorph Candida sphaerica), Debaryomyces hansenii (anamorph Candida famata), Yarrowia lipolytica and Torulaspora delbrueckii (anamorph Candida colliculosa). The method, which is rapid and easy to perform, could be a useful tool for the identification of yeasts present in dairy products.

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.