According to the Code of Federal Regulations, themaximumresidual
ozone level is 0.4 mg/l when water is bottled (FDA, 2012). However,
there are no official regulations regarding a measurement method for
residual ozone in liquid foods such as apple juice. This may be due to
the rapid decomposition property of ozone. Therefore, we analyzed re-
sidual ozone by the indigo method which is commonly used to deter-
mine the concentration of ozone in water. After ozone treatment,
residual ozone concentration in all samples decreased to below
0.4 mg/lwhenmaintained at 4 °C for 6 h.We also confirmed that resid-
ual ozone increased as the treatment temperature decreased, correlat-
ing with the result of a previous study (Achen and Yousef, 2001). They
reported that the concentration of residual ozone was greatest at 4 °C,
not at 22 or 45 °C.