The objective of this work was to investigate the structure and diversity of lactic acid bacteria (LAB) communities in sourdough used for the production of traditional breads (Carasau, Moddizzosu, Spianata, Zichi) in Sardinia. 16S rDNA sequencing and Randomly Amplified Polymorphic DNA (RAPD-PCR) was applied for the identification and typing of the LAB isolated from 25 samples of sourdoughs. Multivariate statistical techniques were applied to RAPD-PCR pattern to study the biological diversity of sourdough samples. Twelve different species of LAB were identified, and most isolates were classified as facultative heterofermentative lactobacilli. Lactobacillus pentosus dominated the lactic microflora of many samples while Lactobacillus sanfranciscensis was isolated only from a limited number of samples. Although heterofermentative species represented between between 30% and 60% of the isolates in Carasau, Spianata and Zichi sourdoughs, only 2% of the isolates from Moddizzosu sourdoughs were identified as heterofermentative LAB. RAPD-PCR with a single primer followed by cluster analysis did not allow the identification of the isolates at the species level. However, a multidimensional scaling/bootstrapping approach on the RAPD-PCR patterns uncovered the diversity of the LAB communities of LAB showing differences both within and between bread types.

The evolution of microflora, carbohydrates and lactic acid isomers was studied in Pecorino Romano cheese, and the isomerization of L(+) and D(-) lactic acid was examined during the ripening period by means of C-14 labelled compounds. Only small quantities of D(-) lactic acid were found by enzymatic analysis, compared to the L(+) isomer. The former continued increasing until 30 days, while the L(+) form decreased after the first days of ripening. The experiments carried out by means of radiotracers, indicated that both isomeric forms of lactic acid are subject to isomerization, which means that also the D(-) form is transformed into L(+) isomer. A quite high number of non-starter bacteria, such as yeasts, propionic acid bacteria and Micrococcaceae, were observed inside and outside the cheese. The linear relationship between microbial count and the metabolic compounds was determined, and significant coefficients were found confirming that non-starter microflora could be involved in the transformation of these metabolic compounds.

Streptococci from different collections and dairy materials were characterized by conventional and molecular methods. After amplification of the 16S–23S rDNA spacer region, all the strains referable to the genus Streptococcus exhibited a single polymerase chain reaction (PCR) product, allowing their differentiation from enterococci. Cleaving this PCR product with Hae III, two different restriction patterns could be observed, allowing Streptococcus salivarius DSM 20560T, Strep. thermophilus NCDO 822 and two strains of Streptococcus spp. to be gathered in one group and all the other strains in another. In order to achieve strain typing, all the cultures were investigated by random amplified polymorphic DNA (RAPD)‐PCR analysis employing two selected primers. The results were treated by cluster analysis, appearing significantly consistent with both the taxonomic position and the origin of the strains. Pulsed‐field gel electrophoresis (PFGE) of Sma I digests of the genomic DNA from 11 representative strains with decreasing levels of RAPD similarity allowed their diversity to be confirmed, even though RAPD‐PCR proved to be less discriminating than PFGE analysis. The results are discussed with reference to the capability of the analytical procedures used to aid both identification and strain typing of streptococci, as well as the taxonomic structure of the species Strep. thermophilus.

A study of the lactic microflora on Sardinian table olives and in the corresponding pickling solution revealed the presence of Streptococcus faecium with the typical microbial species.The use of Str. faecium in the preparation of table olives together with Lactobacillus plantarum and Saccharomyces cerevisiae produced rapid, regular and complete fermentation of the pickling solution.Even in conditions of high pH and salinity, Str. faecium produced large quantities of aromatic compounds and proved to start lactic fermentation more quickly, thus increasing the L(+) lactic acid concentration, which is useful to human nutrition. Sacch. cerevisiae also acted favourably on the aroma and furthermore improved colour, taste and firmness. On the other hand, it partially degraded the lactic acid.The use of a mixed starter containing lactic acid bacteria and yeasts would seem to be a promising method of processing and standardisation of table olives production. Furthermore, the risk of extraneous contamination is minimized.