It has been reported that ozone treatment is more effective when
microorganisms are suspended in pure water or buffers containing
less ozone demanding materials than in complex food systems com-
posed of organic compounds (Cho et al., 2003). Ozone concentration
in treated apple juice couldn't be determined by the indigo method
(data not shown) because of the intrinsic color of juice, but residual
ozone in distilledwater could be analyzed. Even thoughwe obtained re-
sults about residual ozone by using distilledwater instead of apple juice,
low concentrations of residual ozone may occur in apple juice due to
various ozone consuming compounds compared to distilled water.
There are organic compounds such as sugars, pectic substances, and an-
tioxidants in apple cider and orange juice. These compounds may react
with ozone (Kim et al., 1999; Williams et al., 2004). Antioxidant com-
pounds like polyphenols, phenolic acids, flavonoids and ascorbic acid
are ozone consuming materials having an effect on ozone chelation in
apple juice (Liao et al., 2007). Therefore, application of the indigometh-
od in this study is considered reasonable for judging the concentration
of residual ozone in apple juice by inference through results obtained
from distilled water.