Animal rennets as sources of dairy lactic acid bacteria

The microbial composition of artisan and industrial animal rennet pastes was studied by using both culture-dependent and -independentapproaches. Pyrosequencing targeting the 16S rRNA gene allowed to identify 361 operational taxonomic units(OTUs) to the genus/species level. Among lactic acid bacteria (LAB), Streptococcus thermophilus and some lactobacilli, mainlyLactobacillus crispatus and Lactobacillus reuteri, were the most abundant species, with differences among the samples. Twelvegroups of microorganisms were targeted by viable plate counts revealing a dominance of mesophilic cocci. All rennets were ableto acidify ultrahigh-temperature-processed (UHT) milk as shown by pH and total titratable acidity (TTA). Presumptive LABisolated at the highest dilutions of acidified milks were phenotypically characterized, grouped, differentiated at the strain levelby randomly amplified polymorphic DNA (RAPD)-PCR analysis, and subjected to 16S rRNA gene sequencing. Only 18 strainswere clearly identified at the species level, as Enterococcus casseliflavus, Enterococcus faecium, Enterococcus faecalis, Enterococcuslactis, Lactobacillus delbrueckii, and Streptococcus thermophilus, while the other strains, all belonging to the genus Enterococcus,could not be allotted into any previously described species. The phylogenetic analysis showed that these strains mightrepresent different unknown species. All strains were evaluated for their dairy technological performances. All isolates produceddiacetyl, and 10 of them produced a rapid pH drop in milk, but only 3 isolates were also autolytic. This work showed that animalrennet pastes can be sources of LAB, mainly enterococci, that might contribute to the microbial diversity associated with dairyproductions.