DGGE analysis of yeast and lactic acid bacteria populations during the production process of Panettone

Panettone is a traditional Italian Christmas cake, manufactured using a continuously reproduced sourdough, the so-called “mother”, that consists of a natural mixed culture including yeasts, mainly responsible for leavening, and lactic acid bacteria (LAB), which primarily cause dough acidification. The metabolic activities of this heterogeneous microbial population are of fundamental importance for texture, flavor and shelf-life of the final products. In order to highlight the microbial species involved in fermentation of Panettone, and their dynamics along the production process, a culture independent approach, based on denaturing gradient gel electrophoresis (DGGE), was chosen as the most suitable one. Dough samples (from the mother to the final dough) were withdrawn from the production process of three types of Panettone manufactured in one bakery of Central Italy using different recipes and process techniques. Microbial DNA, directly extracted from dough samples, was subjected to amplification of variable regions of the 16S rRNA and 28S rRNA genes. Molecular fingerprinting of cultivable plus non cultivable LAB and yeasts, were determined by DGGE analysis. In parallel, DNA extracted from bulks of LAB cells, formed by harvesting colonies from the serial dilution agar plates of two culture media, was used to profile the “cultivable” community, through PCR-DGGE. Simple indexes were also calculated on the basis of the DGGE profiles, to allow an objective evaluation of LAB and yeast biodiversity to be obtained. The two different molecular approaches revealed to be useful in order to define the main LAB and yeast species involved in Panettone fermentations and their dynamics