Molecular and functional diversity of lactic acid bacteria and yeasts characterizing sourdough tuscan bread

Traditional bread is produced using sourdough, a biological complex of lactic acid bacteria and yeasts. Their metabolic end-products affect the nutritional, organoleptic and technological traits of bread. The diversity of the microbial strains depends on process technology, type of flour used and other ingredients traditionally associated with local culture and origin. Therefore, sourdough microbiota is specific of each bread type. In this study the sourdough used to produce Tuscan bread was characterized by using both culture-dependent and culture-independent methods (PCR-DGGE). From a pool of the 516 strains isolated in pure culture, 96 lactic acid bacteria and 68 yeasts were identified by Amplified Ribosomal DNA Restriction Analysis (ARDRA), RFLP analysis of the internal transcribed spacer regions (ITS) and sequence analysis. All lactic acid bacteria were identified as Lactobacillus sanfranciscensis, however ARDRA analysis showed a polymorphism within 16S rDNA gene that allowed the subdivision of L. sanfranciscensis isolates into three groups. Among yeasts, 97% of the isolates were identified as Candida humilis and only 3% as Saccharomyces cerevisiae. Further studies showed specific functional abilities of the isolated microorganisms, such as phytase, amylase and protease activities. PCR-DGGE data confirmed the occurrence of L. sanfranciscensis associated with C. humilis and S. cerevisiae and the absence of microorganisms in the VBNC state. The same molecular method showed that sourdough microbial communities were not affected by the manufacturing environment