Lactobacillus pentosus and Saccharomyces cerevisiae dominate the Italian table olive fermentations

Table olives represent a complex habitat where lactic acid bacteria (LAB) and yeasts co-interact and develop throughout the process. As a result, olives acquire the organoleptic qualities afforded by the local environment which includes the presence of the adventitious microbiota that grows during fermentation.This study is part of a wider project aiming the selection of LAB and yeasts to be used for biological debittering of table olives. Five different cultivar of Italian table olives (Itrana Bianca and Itrana Nera, Peranzana, Nocellara del Belice, Cellina di Nardò and Bella di Cerignola) were studied. Bacterial and yeast diversity was investigated by a polyphasic approach including culture-dependent and culture-independent techniques (e.g. PCR-DGGE). The main microbiota was identified by 26S rRNA and recA gene sequencing and PCR-RAPD fingerprinting. Lactobacillus pentosus and Saccharomyces cerevisiae represented the predominant species at the end of fermentation. PCR-DGGE applied to DNA directly extracted from olive brines highlighted the microbiological complexity of different samples as well as the prevalence of the above species. All the isolates were subjected to technological characterization. In particular, for LAB NaCl tolerance, ability to grow in a synthetic brine (glucose 3g/l, yeast extract 0.5 g/l, NaCl 6% w/v, pH 6) and β-glucosidase activity were investigated, while yeasts were characterized for β-glucosidase, peroxidase, proteolytic and pectinolytic activities. Based on the main results of this study, LAB and yeast strains with particular properties were proposed as a mixed starter cultures for table olive fermentation and evaluated at lab-scale. Preliminary results indicated the suitability of some Lb. pentosus strain inoculated as a starter to dominate the fermentation and reduce the time required for oleuropein hydrolysis with respect to control samples.[...]