Isolation of a Ligilactobacillus salivarius strain from an old cheese stamp and its use as an adjunct culture for cheese-making
In this work, a Ligilactobacillus salivarius strain was isolated from an old cheese stamp, which was last used in 1936. A 16S rRNA-based metataxonomic analysis of the dry dairy scab that covered the stamp revealed that a high percentage of the sequences belonged to the genus Lactobacillus. Subsequently, the strain was used as an adjunct culture in the elaboration of cheeses. A Lactococcus lactis strain was used as the starter culture; parallel, cheeses made using only the starter culture but without adding the L. salivarius strain were also performed as control cheeses. All the cheeses were matured for up to 6 months. Samples were collected at 0, 60, 120, 180 and 240 days of ripening. They were submitted to standard dairy analysis. In addition, volatile compounds of samples collected at days 60, 120, 180 and 240 were extracted by automated solid-phase microextraction and analyzed by gas chromatography-mass spectrometry. A metataxonomic analysis was also performed with samples obtained at the beginning, in the middle and at the end of the ripening process. Finally, the cheeses were submitted to a sensorial analysis. The results showed that the use of the L. salivarius strain as an adjunct culture promoted the formation of some volatile compounds that led to a better valuation in the organoleptic analysis in comparison to control cheeses. Production of such compounds and sensorial valuation increased as the ripening period increased. The metataxonomic analysis showed that the percentage of Lactobacillus sequences increased over the ripening time. To our knowledge, this is the first time that a L. salivarius strain has been used as an adjunct in the manufacture of sheep cheeses and our results showed that it increases the organoleptic properties of cheeses.