thermophilus
and L. delbrueckii subsp. bulgaricus were inoculated
together into either cows' milk or soy beverage. Twelve hours
were required to reach a pH of 4.3 in both cases (Fig. 1). The S.
thermophilus and L. delbrueckii subsp. bulgaricus strains used
in this study grew well in the soy beverage and their population
stabilized after 6 h and 10 h incubation, respectively. When
cows' milk was inoculated with both S. thermophilus and
L. delbrueckii subsp. bulgaricus, their numbers increased
steadily during the 12 h fermentation. After 12 h, the numbers
of S. thermophilus in both the cows' milk and the soy beverage
were higher than those of L. delbrueckii subsp. bulgaricus.
The final pH value of both milk and soy beverage were
similar (Fig. 1), but the pH declined faster in the soy beverage
than in the cows' milk.
The presence of the probiotics did not affect the growth
patterns of the yogurt strains, and there were many phenomena
that were constant in all the treatments (Figs. 1–5). Data are
presented in one Fig. 2a to illustrate typical means and standard
errors of the means. In all cases, S. thermophilus growth was
faster in soy beverage than in milk; growth of L. delbrueckii
subsp. bulgaricusi was always slower in soy beverage than in
milk; S. thermophilus growth in soy stopped after about 6 h
incubation with numbers at approximately 2×108 cfu/ml; in both
the soy beverage and cows' milk the growth of L. delbrueckii
subsp. bulgaricus was slower than that of S. thermophilus but