MICROBIAL COMMUNITY MODIFICATION IN DOUGH USING LEUCONOSTOC CITREUM C2.27 AS A STARTER

Leuconostoc citreum C2.27 (ITEM 17404, http://server.ispa.cnr.it/ITEM/Collection/) was used as a starter for the preparation of focaccia, a typical Apulian flat-bread, according to a "yeast free" protocol (De Bellis et al., 2019). The microbial diversity in focaccia doughs was evaluated by plate count and culture-independent approaches using a focaccia dough with 2% (w/w) baker's yeast and without starter strain, as a control. The doughs and flours were subjected to microbiological analyses and the amount of cultivable total lactic acid bacteria (LAB), yeasts and molds was determined. Presumptive LAB and yeasts were genetically characterized by rep-PCR. Then, bacterial strains were identified by sequencing the 16S rRNA gene, while yeasts were identified by sequencing the D1/D2 domain of 26S rDNA (De Bellis et al, 2019). The experiment was repeated in triplicates. Microbiological analyses showed the absence of yeasts in the focaccia dough inoculated with the starter L. citreum C2.27. In this preparation the starter strain dominated the microbial community. The control dough showed a very high count of yeasts, identified as Saccharomyces cerevisiae, while the population of LAB was significantly lower than that observed in the dough inoculated with the starter, although characterized by a higher microbial diversity. In order to study the influence of starter strain on bacterial microbiota of focaccia dough, a metagenomic analysis has been carried out. The analysis of microbiota was performed by sequencing the V5-V6 hypervariable region of 16S rRNA gene. After quality filtering and chimera detection, reads were aligned against SILVA ribosomal RNA sequence database (https://www.arb-silva. de/) using MALT (Herbig et al., 2016). Taxonomic binning was performed with MEGAN Community Edition software v6.12 (Huson et al., 2016). The results indicated that the V5-V6 hypervariable region of 16S rRNA was suitable for studying the bacterial microbiota of doughs, highlighting a significant difference in bacterial community of focaccia dough with baker's yeast respect to dough inoculated with the starter strain. Moreover, results confirmed that L. citreum C2.27 was able to dominate the microbial environment.