Microbial dynamics of model Fabriano-like fermented sausages as affected by starter cultures, nitrates and nitrites

The present study promotes the valorization of Fabriano-like fermented sausages, which are central-Italy salami with an origin that dates to the early 17th century, for the possible future selection of autochthonous starter cultures to be used with respect to local traditions. To the best of the authors' knowledge, this study represents the first attempt to define the microbial dynamics in Fabriano-like fermented sausage and the effect of nitrates/nitrites and starter cultures on its natural bacterial biota. Culture and RNA-based techniques (RT-PCR-DGGE and Illumina sequencing) were used to assess the microbial ecology of model Fabriano-like fermented sausages together with the impact of starter cultures and different nitrate and nitrite concentrations. The meat batter was used to produce two batches of fermented sausages that were prepared as follows: i) without commercial starters or ii) with the use of starter cultures composed of Pediococcus pentosaceus and Staphylococcus xylosus. Each batch was further divided into three different batches with the addition of 0/0 mg kg^-1 nitrate/nitrite, 75/60 mg kg^-1 nitrate/nitrite and 150/125 mg kg^-1 nitrate/nitrite to the first, second and third batch, respectively. The samples, which were produced in triplicate, were analyzed on the day of production and after 7, 21, and 42 days of ripening. Enterobacteriaceae counts were always higher in model Fabriano-like sausages produced without the use of starter cultures at all of the sampling times irrespective of the tested nitrate/nitrite concentrations. Lactobacilli counts were positively influenced by the starters, although this influence was not evident over time; moreover, the effect of nitrates and nitrites on the counts of lactobacilli differed over time. As a general trend, coagulase-negative cocci counts were apparently not influenced by the tested nitrate/nitrite concentrations. Regarding the effect of nitrates/nitrites on the microbial diversity revealed by RT-PCR-DGGE, the higher the concentration, the lower the presence of some genera/species such as Pseudomonas spp., Serratia liquefaciens and Staphylococcus spp. However, Illumina sequencing detected Pseudomonas spp. as a minority species after 7, 21 and 42 days of ripening irrespective of the nitrate/nitrite concentration. The presence of Staphylococcus species was highlighted by both RT-PCR-DGGE and Illumina sequencing at all of the stages of ripening, although its presence was massively detected in fermented sausages produced without the use of nitrates/nitrites at the end of ripening. Overall, the data collected clearly highlighted the dominance of Lactobacillus sakei in all of the fermented sausages during ripening (from day 7 to day 42) and irrespective of the nitrate/nitrite concentration and added starter cultures. Moreover, Pediococcus spp. was principally detected in model Fabriano-like fermented sausage with added starter cultures irrespective of the nitrate/nitrite concentration.