Fig. 1A shows the pH change and viable counts for B. subtilis and
L. bulgaricus during fermentation when two strains were simultaneously
inoculated into steamed red beans. The maximum number
of viable cells (9.55 log CFU g1) of B. subtilis was detected after
incubation for 24 h. L. bulgaricus had a peak growth
(8.94 log CFU g1) after 72 h of incubation. The pH of the red beans
increased during fermentation, indicating that protein degradation
exceeded sugar fermentation.
L. bulgaricus was inoculated after B. subtilis was allowed to grow
for 48 h (Fig. 1B). The pH changes and growth of B. subtilis during
the fermentation period were similar to that of the two starter
cultures that were simultaneously inoculated. L. bulgaricus was
inoculated two days after the growth of B. subtilis because we expected
L. bulgaricus to grow fast in an anaerobic environment,
which was created once oxygen was depleted by the aerobic
growth of B. subtilis. Surprisingly, L. bulgaricus did not grow and
died quickly under these conditions. The pH changes and growth of
B. subtilis during the fermentation period were similar to those
when the two starter cultures were simultaneously inoculated.We
suspected that substances produced by B. subtilis might be toxic to
L. bulgaricus.