Probiotic features of Lactobacillus strains isolated from Ragusano and Pecorino Siciliano cheeses.

In the present study 177 Lactobacillus spp. strains, isolated from Ragusano and Pecorino Siciliano cheeses, were in vitro screened for probiotic traits, and their characteristics were compared to those of Lactobacillus rhamnosus GG, commercial strain. Based on acidic and bile salt resistance, thirteen Lactobacillus strains were selected. The multiplex-PCR application revealed that nine strains belonged to L. rhamnosus species and four to Lactobacillus paracasei species. All selected strains were further investigated for transit tolerance in simulated upper gastrointestinal tract (GI), for adhesion capacity to human intestinal cell lines, for hydrophobicity, for co-aggregation and auto-aggregation and for antimicrobial activities. Moreover, antibiotic resistance, hemolytic and bile salt hydrolase activities were investigated for safety assessment. Viable counts after simulated gastric and duodenal transit revealed that overall the selected lactobacilli tolerated better pancreatic juice and bile salts than acidic juice. In particular, three L. rhamnosus strains (FS10, FS2, and PS11) and one L. paracasei strain (PM8) increased their cell density after the simulated GI transit. The same strains showed also high percentage of auto-aggregation and co-aggregation with Escherichia coli. All strains were effective against both Staphylococcus aureus and E. coli and variability was achieved versus Listeria monocytogenes and Enterococcus faecalis used as pathogenic indicator strains. Different behavior was revealed by strains for adhesion ability and hydrophobicity, which are not always linked each other and are strongly strain-dependent. From the safety point of view, no isolate showed hemolytic and bile salt hydrolase activities, except one, and most of the strains were sensitive to a broad range of clinical antibiotics. This work showed that the L. rhamnosus FS10 and the L. paracasei PM8 are good promising probiotic candidates for further in vivo investigations.

Pecorino Crotonese cheese: study of bacterial population and flavour compounds.

The diversity and dynamics of the dominant bacterial population during the manufacture and the ripening of two artisanal Pecorino Crotonese cheeses, provided by different farms, were investigated by the combination of culture-dependent and -independent approaches. Three hundred and thirty-three strains were isolated from selective culture media, clustered using Restriction Fragment Length Polymorphism and were identified by 16S rRNA gene sequencing. The results indicate a decrease in biodiversity during ripening, revealing the presence of Lactococcus lactis and Streptococcus thermophilus species in the curd and in aged cheese samples and the occurrence of several lactobacilli throughout cheese ripening, with the dominance of Lactobacillus rhamnosus species. Bacterial dynamics determined by Denaturant Gradient Gel Electrophoresis provided a more precise description of the distribution of bacteria, highlighting differences in the bacterial community among cheese samples, and allowed to detect Lactobacillus plantarum, Lactobacillus buchneri and Leuconostoc mesenteroides species, which were not isolated. Moreover, the concentration of flavour compounds produced throughout cheese ripening was investigated and related to lactic acid bacteria presence. Fifty-seven compounds were identified in the volatile fraction of Pecorino Crotonese cheeses by Gas Chromatography-Mass Spectrometry. Esters, alcohols and free fatty acids were the most abundant compounds, while aldehydes and hydrocarbons were present at low levels.

Effect of wild strains used as starter cultures and adjunct cultures on the volatile compounds of the Pecorino Siciliano cheese.

The effect of six wild strains on the volatile profile of the PS cheese was investigated and compared to that generated from industrial starters generally used to produce PS cheese. All cheeses were subjected to microbiological, physicochemical, and volatile compounds analyses. The DGGE of the 16S rDNA analysis was also applied. The volatile compounds generated during ripening were studied through the SPME and the GC-MS methods. No difference was detected between the experimental and control cheeses throughout chemical and microbiological analyses, while the DGGE results showed the presence of Streptococcus thermophilus in all cheeses, and the dominance of Enterococcus durans, Lactobacillus rhamnosus, and Lactobacillus casei in most of the experimental cheeses. Moreover, the presence of Lactococcus lactis species as in the control and in the experimental P2 and P4 cheeses was also revealed. The SPME results showed more pronounced volatile compounds in the experimental cheese samples than in the control ones.