continued for a longer time; and after 6 h incubation,
S. thermophilus was dominant, but after 12 h the ratios of the
numbers of S. thermophilus to those of L. delbrueckii subsp.
bulgaricus were close to 1:1 in milk, and approximately 2:1 in soy
beverage.
The probiotic strains did not have an obvious effect on
acidification. In all cases (Figs. 1–5), the drop in pH was faster
in soy beverage than in milk, and the pH values after 12 h
incubation at 41 °C were not greatly affected by the presence of
the probiotic strains.
3.2. Growth of the probiotic strains
Approximately 2 log increases in the numbers of both
L. rhamnosus GG and L. johnsonii La-1 were observed when
either of these probiotic strains was added together with the
yogurt strains in cows' milk (Figs. 2a, 3a) or the soy beverage
(Figs. 2b, 3b). The numbers of both L. rhamnosus GG and
L. johnsonii La-1 were less than the numbers of the yogurt
bacteria after 12 h fermentation. Although acidification was
faster in the soy beverage than in milk, growth of both probiotic
lactobacilli was more extensive in the soy beverage than in
milk. This resulted in L. rhamnosus GG and L. johnsonii La-1
populations being respectively 3 and 5 times higher in the
fermented soy beverage than in the fermented milk after 12 h