|Abstract or Summary
- Streptococcus lactis C2F and Streptococcus cremoris 459 grew
to a maximum population of 1 to 2 x 10⁹ colony forming units (cfu)/ml with a generation time of 96 min in 11% nonfat dry milk (NFDM)
under static conditions at 22° C.
Streptococcus diacetilactis 18-16
grew to a maximum population of 7 x
with a generation
time of 95 min under the same conditions.
Incubation of S. lactis
C2F at 28° to 30° C resulted in a reduction of the generation time to
60 min but no significant increase in the maximum population.
Maintaining the pH of S. lactis C2F cultures at 6.3 with sodium
hydroxide, potassium hydroxide or calcium hydroxide increased the
maximum population to 4.5 to 5.5 x
10⁹ cfu/ml. When ammonium
hydroxide, sodium carbonate or ammonium carbonate were used as
neutralizing agents a maximum population of 8.4 to 8.9 x
resulted. No significant change in generation time was observed except when ammonium hydroxide was used as the neutralizer when
the generation time was reduced to 44 min. Sodium lactate formed
during growth of S. lactis C2F cultures in which the pH was maintained with sodium carbonate was established as a contributing factor
in limiting the maximum population.
Increasing the percentage of
NFDM above 11% (s/v) did not increase the maximum
However, there was an increase in the maximum population
to 1.0 x
cfu/ml when pH-controlled S. lactis C2F cultures were
sparged with nitrogen gas at a low flow rate (controlled growth).
S. cremoris 459 grown under these conditions (pH
6.3, 30° C) in
NFDM had a generation time of 66 min and reached a maximum population of 8.7 x
Under the same conditions, S.
diacetilactis 18-16 grew to a maximum population of 9.4 x
in NFDM but only when the milk was supplemented with
Concentrates of S. lactis C2F, S. cremoris 459 and S.
diacetilactis 18-16 were prepared by adjusting NFDM cultures in the
late logarithmic growth phase under controlled growth conditions,
to pH 6.9 and adding sodium citrate to a final
concentration of 4.5 %.
Cells were harvested from the partially cleared medium by centrifugation.
The sedimented cells were reconstituted to one-tenth the
original culture volume, lyophilized and stored at -196, -22, +7 and
+22° C. Lyophilization of S. lactis C2F cell concentrates (5.5 x
cfu /ml) in 10% nonfat milk caused a 31% reduction in
activity of the cells measured immediately after freeze drying.
the cells were suspended in 5% monosodium glutamate,
was reduced to a 14% loss and use
of 5% trehalose resulted in only a
6% loss in activity.
Lyophilization of S. cremoris 459 and S.
diacetilactis 18-16 cell concentrates in 5% monosodium glutamate,
containing 4.2 x
and 4.6 x
10¹⁰ cfu/ml respectively, caused a
loss in activity of 31% for S. cremoris and 7% for S.
Using activity of the lyophilized concentrate as
100%, the concentrates of S. lactis C2F cells lyophilized in
10% NFDM and stored
at +22 and +7° C showed greater than 80% decrease
activity in seven days, 64% at -22° in 21 days and no
21 days at -196° C.
Lyophilization of S. lactis C2F cell concentrate
in 5% monosodium glutamate showed a reduction
in activity of 70%
in 21 days when stored at +22 and +7° C.
Lyophilization of S. lactis
C2F cell concentrates in 5% monosodium glutamate
with 0.16 M potassium iodide resulted in a 32% and 20%
in activity when stored at +22 and +7° C respectively
for 21 days;
there was no loss when stored at -22 and -196° C.
The addition of
0.05% ascorbic acid or 0.05% butylated
hydroxyanisole did not
appreciably alter the results obtained with the use of glutamate
alone. There was no reduction in activity after 28 days of storage of
lyophilized cell concentrates of S. lactis C2F, S. cremoris 459 or
S. diacetilactis 18-16 when stored under vacuum in 5%
glutamate at +22°, +7°, -22°, or -196° C.
of S. lactis C2F stored in 10% NFDM under vacuum
also showed no
reduction in activity at +22°, +7°, -22° and -196° C.