PCR detection of Lactobacillus sanfranciscensis in sourdough and Panettone baked product

Sourdoughs, in which Lactobacillus sanfranciscensis is the predominant bacterial species, are distinctive of some traditional Italian sweet baked products like Panettone. The direct extraction of amplifiable bacterial DNA from products subjected to heat treatment represents a valid tool to identify and trace microbial species originally present in the food matrices. Three types of protocols for the isolation and clean-up of DNA (CTAB, Wizard^® DNA Clean-Up System, NucleoSpin^® Food) were applied on mother, final dough and end-product samples and compared through the determination of the maximum amplifiable dilution by a PCR reaction targeting two fragments (1460 and 153 bp long) of 16S rDNA region of Lb. sanfranciscensis. CTAB extracting protocol was revealed to be the best for isolating DNA. In dough samples the amplification with the 153 bp fragment showed signals at concentration levels that are comparable with the values obtained from the plate counts, and two log cycles higher than those found with the amplification targeting the 1460 bp fragment. In the cooked samples only the 153 bp amplicon was detected, indicating that oven cooking degrades DNA into small fragments.