Similarly with the ascorbate autoxidation
ability and reducing activity of kefir samples, the
superoxide anion scavenging effect of samples
increased as the soymilk ratio was raised (Table
2). According to Duncan grouping, this activity
sharply increased in kefirs containing at least
again 50% soymilk. It has been reported that
antioxidant properties of some flavonoids are
effective mainly via scavenging of superoxide
anion radical (Yen & Duh 1994). Thus, the higher
superoxide anion scavenging effect values in
those kefir samples can be attributed to soymilk
originated isoflavones. Moreover, soybeans
contain superoxide dismutase which possesses the
superoxide anion scavenging effect by catalyzing
the conversion of superoxides to hydrogen
peroxide and oxygen (Liu et al 2002).
Decomposition of excess superoxides by
superoxide dismutase is an important
physiological antioxidant defense mechanism in
aerobic organisms. It has been indicated that some
Lactococcus spp. (Sanders et al 1995; Lin & Yen
1999) and S. thermophilus (Archibald &
Fridovich 1981) are able to express antioxidative
enzyme superoxide dismutase activity. So the
bacterial flora mainly the homofermentative lactic
acid bacteria in kefir samples could positively
affect the superoxide anion scavenging effect