Supplementation of plant extracts as prebiotics obviously
decreased the fermentation time and increased
the viability of the yogurt starter cultures when compared
with control yogurt. Fructose and glucose in
the plant extracts were used as energy sources by the
starter cultures. In addition, fortification of yogurt with
the plant extracts also led to an increase in lactic acid
and pyruvic acid contents and a decrease in formic acid
and propionic acid contents. Formic acid functioned
to enhance the growth of LAB. Moreover, hydroxycinnamic
acid, such as neo-chlorogenic, chlorogenic, and
caffeic acid, in the plant extracts was degraded and metabolized
during yogurt fermentation, which might be
attributed to the fermentation properties of the plant
extract-supplemented yogurts. Further, substantially
higher antioxidant activities were observed for the yogurts
with plant extracts than for nonsupplemented
yogurt, concomitant with higher TPC. The improved
fermentation and antioxidant properties of the yogurts
were related to the phenolic compounds in CT and MA
extracts; especially, CT-supplemented yogurts showed
the greatest antioxidant activities. Therefore, the addition
of CT extract to yogurt has the potential to be
further developed for consumers as a functional yogurt
with antioxidant properties.