Exploitation of lactic acid bacteria and yeasts in traditional Sicilian sourdough

It is noteworthy that the dynamic equilibrium between yeasts and lactic acid bacteria (LAB) in sourdough ecosystem confers positive nutritional, organoleptic, textural properties to the final products. Among factors affecting the diversity and stability of sourdough microbiota, the wheat grain cultivar plays a crucial role. Although the microbiota of many types of sourdough was characterized, no information is available on Maiorca sourdough. Maiorca is an ancient white wheat grain cultivated in Sicily, recently appreciated for its low gluten content and the high-quality flour, suitable for bread making. Four samples of Maiorca sourdough were kindly provided from bakeries, located in Sicily, and in depth studied from the microbiological and chemical point of view. In detail, along microbiological analysis, both yeast and LAB populations were investigated using an integrated approach based on culture-dependent and independent methods. In detail, total DNA was isolated directly from samples and subjected to PCR-DGGE analysis. In addition, to isolate LABs, MRS media differently modified were set up and the isolates were clustered based on the 16S rDNA PCR-RFLP profiles. Yeast isolates were identified by analysing two portions of the 35S rDNA cistron and the segment including the D1/D2 domains of the 26S rRNA gene and the internal transcribed spacers (ITS) 1 and 2. Yeasts and LABs taxonomic affiliation was assessed using the BLAST software in the GENBANK database. Yeast genotyping was carried out by (GAC)5 and (GTG)5-based micro/minisatellite primed-PCR (MSP-PCR). Sourdough samples were also subjected to SPME-GC-MS analysis in order to detect the VOCs profile. Microbiological analyses revealed that LAB and yeast population exhibited quite similar cell density, in discordance to previous reports. PCR-DGGE analysis, of the V3-V4 region of LAB 16S rRNA gene of LAB and of the partial D1/D2 domain of 26S rRNA gene of yeasts, revealed a high biodiversity within LAB and yeast biota. Based on the PCR-RFLP profiles, the LAB isolates (31) were grouped into 4 different clusters while 5 different profiles were generated by yeast isolates (25). (GTG)5 and (GAC)5 MSP-PCR showed different genotypic profiles from isolates belonging to the same species indicating an effective differentiation at subspecies level. SPME-GC-MS analysis revealed different VOCs profile among samples allowing to identify 14 different compounds as alcohols, esters, aldehydes, and alkanes. Among alcohols, the 1-pentanol was the most abundant compound, and among esters, acetic acid hexyl ester was detected in all sourdough samples, generating a fermented, bready and fruity smell. Conclusions: Data of the present study underlined that Maiorca sourdough was co-dominated by LAB and yeast population. The high LAB and yeast species diversity was positively correlated to VOC compounds able to generate fermented, bready and fruity smell, suggesting a promising combination of raw materials and fermentation process for the production of bakery products with aromatic properties.