To estimate the suitability of cultured milk for the subsequent
growth of
dairy lactic acid bacteria in cheese manufacturing, control milk was first
cultured
until the end of the exponential phase with one of four proteolytic (Prt+)
strains of Lactococcus lactis differing in their proteolytic enzymes,
and pasteurized after
readjusting the pH to its initial value. Nineteen non-proteolytic (Prt−)
strains of Lc. lactis and nine Leuconostoc mesenteroides
strains of dairy origin were then grown in
the precultured milk until the stationary phase and their growth was compared
with
that in control milk. Despite the accumulation of non-protein N (NPN) during
preculture, the growth of most Prt−
strains of Lc. lactis in precultured milk was either
reduced or unchanged whereas that of Ln. mesenteroides strains
was unchanged or
slightly stimulated. This reduction in growth was reversed by adding an
NPN source
to precultured milk, indicating that it was due to the exhaustion of assimilable
NPN
in precultured milk. Thus, preculturing milk with Prt+
strains of Lc. lactis could not
be recommended for promoting the subsequent growth of starter cultures
in cheese
manufacturing.