In vivo application and dynamics of lactic acid bacteria for the four-season production of Vastedda-like cheese.

Twelve lactic acid bacteria (LAB), previously selected in vitro (Gaglio et al., 2014), were evaluated in situ for theirpotential to act as starter cultures for the continuous four-season production of Vastedda-like cheese, madewithraw ewes' milk. The strains belonged to Lactobacillus delbrueckii, Lactococcus lactis subsp. cremoris, Leuconostocmesenteroides subsp. mesenteroides and Streptococcus thermophilus. LABwere first inoculated in multiple-straincombinations on the basis of their optimal growth temperatures in three process conditions which differed formilk treatment and medium for strain development: process 1, growth of strains in the optimal syntheticmedia and pasteurised milk; process 2, growth of strains in whey based medium (WBM) and pasteurisedmilk; and process 3, growth of strains in WBM and raw milk. The strains that acidified the curds in short time,as shown by a pH drop, were all mesophilic and were then tested in a single inoculum through process 3. Randomlyamplified polymorphic DNA (RAPD)-PCR analysis applied to the colonies isolated from the highest dilutionsof samples confirmed the dominance of the added strains after curd acidification, stretching and storage.After 15 days of refrigerated storage, the decrease in pH values showed an activity of the mesophilic strains atlow temperatures, but only Lc. lactis subsp. cremoris PON153, Ln. mesenteroides subsp. mesenteroides PON259and PON559 increased their number during the 15 days at 7 °C. A sensory evaluation indicated that the cheesesobtained by applying protocol 3 and by inoculation with lactococci are the most similar to the protected denominationof origin (PDO) cheese and received the best scores by the judges. Thus, the experimental cheeses obtainedwith raw milk and inoculated with single and multiple combinations of lactococci were subjected to theanalysis of the volatile organic compounds (VOCs) carried out by a headspace solid phase microextraction(SPME) technique coupled with gas chromatography with mass spectrometric detection (GC/MS). The dominanceof lactococci over thermophilic LAB of raw milk was verified during summer production and, based onthe combination of VOC profiles and sensory evaluation of the final cheeses, the multi-strain Lactococcus cultureresulted in the most suitable starter preparation for the full-year production of Vastedda-like cheese.