Purpose: This study evaluated Lactococcus lactis subsp. cremoris M104 and Enterococcus faecium GL31 as co-starter adjuncts in the production of PDO Galotyri cheese by a traditional method. Strains M104 and GL31 possess probiotic properties and produce nisin A and enterocin A, respectively, in milk.
Methods: Both strains were challenged against Listeria monocytogenes (LM) and Staphylococcus aureus (SA) in co-culture with a commercial thermophilic starter culture (CTSC) in pre-sterilized ewes’ milk incubated at 37oC for 6 h and then shifted to 22oC for additional 42 h. Afterwards, combinations of the CTSC+M104 or the CTSC+M104+GL31 were used to produce Galotyri cheeses, which were evaluated microbiologically and for pH and sensory quality.
Results: Both pathogens increased by ca. 2 log units in all milk cultures after 6 h at 37oC. Following that, however, LM growth was inhibited completely by strain GL31 while strain M104 caused a 2-log reduction in LM viability. Growth and survival kinetics of SA were similar to LM after 24 h. At 48 h, however, SA was minimized in the presence of strains M104 and GL31. Both bioprotective LAB strains grew at levels higher than 7 to 8 log CFU/g in the presence of the CTSC in Galotyri cheeses, which had a pH below 4.4 and were of high microbiological and sensory quality.
Significance: Lactococcus lactis subsp. cremoris M104 and E. faecium GL31 are suitable for use as co-starter adjunct cultures to produce traditional PDO Galotyri cheese of high nutritional value and quality.