Use of molecular methods for the identification of yeast associated with table olives.

A molecular approach is used for the identification of yeast isolated from table olives. Our results validate those obtained in the past by the classical biochemical methodology. Yeast were isolated from both aerobically and anaerobically processed black table olives and also from canned seasoned green table olives. Molecular identification methodology used included restriction pattern analysis of both PCR-amplified 5.8S rRNA gene and internal transcribed spacers ITS(1) and ITS(2). For some species, sequence analysis of the 26S rRNA gene was necessary. These techniques allowed the identification of three yeast species (Issatchenkia occidentalis, Geotrichum candidum and Hanseniaspora guilliermondii) which had not been described previously in table olives. Saccharomyces cerevisiae and Candida boidinii were the most frequent species in green seasoned olives and processed black olives, respectively. The molecular study of total DNA variability among the S. cerevisiae strains isolated indicates a quite heterogeneous population, with at least four different restriction patterns.

The role of indigenous yeasts in traditional Irish cider fermentations.

AIMS: To study the role of the indigenous yeast flora in traditional Irish cider fermentations. METHODS AND RESULTS: Wallerstein laboratory nutrient agar supplemented with biotin, ferric ammonium citrate, calcium carbonate and ethanol was employed together with PCR-restriction fragment length polymorphism analysis of the region spanning the internal transcribed spacers (ITS1 and ITS2) and the 5.8S rRNA gene in the identification of indigenous yeasts at the species level, from traditional Irish cider fermentations. By combining the molecular approach and the presumptive media it was possible to distinguish between a large number of yeast species, and to track them within cider fermentations. The Irish cider fermentation process can be divided into three sequential phases based on the predominant yeast type present. Kloeckera/Hanseniaspora uvarum type yeasts predominate in the initial 'fruit yeast phase'. Thereafter Saccharomyces cerevisiae type yeast dominate in the 'fermentation phase', where the alcoholic fermentation takes place. Finally the 'maturation phase' which follows, is dominated by Dekkera and Brettanomyces type yeasts. H. uvarum type yeast were found to have originated from the fruit. Brettanomyces type yeast could be traced back to the press house, and also to the fruit. The press house was identified as having high levels of S. cerevisiae type yeast. A strong link was noted between the temperature profile of the cider fermentations, which ranged from 22 to 35 degrees C and the yeast strain population dynamics. CONCLUSIONS: Many different indigenous yeast species were identified. The mycology of Irish cider fermentations appears to be very similar to that which has previously been reported in the wine industry. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has allowed us to gain a better understanding of the role of indigenous yeast species in 'Natural' Irish cider fermentations.