Intracellular peptidases of Lactobacillus helveticus may play a major role
in the proteolysis of Swiss cheeses, provided that they are released through bacterial
lysis. Experimental Swiss cheeses were manufactured on a small scale from
thermized and microfiltered milk using as starters (in addition to Streptococcus
thermophilus and Propionibacterium freudenreichii) one of two Lb. helveticus strains,
ITGLH1 and ITGLH77, which undergo lysis to different extents in vitro. All the
cheeses were biochemically identical after pressing. The viability of Lb. helveticus
ITGLH1 and ITGLH77 decreased to a similar extent (96–98%) while in the cold
room, but the concomitant release of intracellular lactate dehydrogenase in cheeses
made with strain ITGLH1 was 5–7-fold that in cheeses made with ITGLH77. Protein
profiles and immunoblot detection of the dipeptidase PepD confirmed a greater
degree of lysis of the ITGLH1 strain. Free active peptidases were detected in aqueous
extracts of cheese for both strains, and proteolysis occurred principally in the warm
room. Reversed-phase HPLC revealed a more extensive peptide hydrolysis for
ITGLH1, which was confirmed by the greater release of free NH2 groups (+33%)
and free amino acids (+75%) compared with ITGLH77. As the intracellular
peptidase activities of ITGLH1 and ITGLH77 have previously been shown to be
similar, our results indicated that the extent of lysis of Lb. helveticus could have a
direct impact on the degree of proteolysis in Swiss cheeses.