Yeast biota associated to naturally fermented table olives from different Italian cultivars

The yeast communities associated with the fermentation of six different cultivars of Italian table olives were studied. Molecular identification of a total of 117 isolates was achieved by a combination of PCR-RFLP of the 5.8S ITS rRNA region and sequencing of the D1/D2 domain of the 26S rRNA gene. In addition, the isolates were differentiated by RAPD-PCR. The yeast population was also monitored by a culture-independent method based on PCR-DGGE analysis. This combined strategy resulted to be a powerful and reliable tool to investigate table olives yeast ecology and revealed that Saccharomyces cerevisiae was present in all the processed olives. Moreover, strains were characterized on the basis of different properties of technological interest. In particular, β-glucosidase, catalase, pectinolytic, xylanolytic, esterase and lipase activities were investigated and the ability to grow up in presence of different salt concentration (5-7.5-10-14-20% w/v) was evaluated. The majority of strains showed catalase activity and none of them expressed pectinolytic, xylanolytic, esterase or lipase activities. Six strains belonging to Pichia galeiformis and six strains of Wicheramomyces anomalus showed β-glucosidase activity. Only 10 S. cerevisiae strains were able to grow in presence of 14% NaCl. The obtained results offer valuable information on yeast population biodiversity and dynamics in naturally fermented Italian table olives and show the potential use of some yeast strains, besides lactic acid bacteria, as a part of mixed starter cultures for table olive fermentation.