It has been suggested that fermented dairy products require
probiotic bacteria at 107 cfu/ml in order to give health effects in
the gastro-intestinal tract when consumed (Ouwehand and
Salminen, 1998). However, in fermented soy products containing
a mixed culture, the numbers of probiotic bacteria might be
insufficient to impart beneficial effects. This study showed that
when the probiotic bacteria population remained below
3×107 cfu/ml while that of the total yogurt starter reached
5×108 cfu/ml, the effects on the final carbohydrate concentrations
are minimal. This suggests that the effects of probiotic
bacteria on sensory properties would also be limited. In some
instances this could be desirable, but not always. The presence
of probiotic bacteria could reduce the levels of n-hexanal and
pentanal compounds responsible for the “bean” flavour of soy
products (Desai et al., 2002) or increase the level of free isoflavones
in soy products (Choi et al., 2002; Tsangalis et al.,
2003).