Results and Discussion
The flavor compounds in pennywort juice containing added
sugar and treated by ultra-high pressure and thermal processes
are shown in Table 1 and 2. High- pressure-treated juice without
addition of sugar contained 49 volatiles (Wongfhun and others
2009), whereas HPP with added sugar contained 56 volatiles. Pasteurized
and sterilized juices without addition of sugar contained
55 volatiles (Wongfhun and others 2009), whereas pasteurized and
sterilized juices with added sugar contained 60 and 74 volatiles, respectively.
This means that sugar brings about increasing volatile
components through the interaction with other compounds in
the food matrix. However, HPP caused more flavor volatiles from
the acyclic alcohols to be retained (P < 0.05), with a trend to
increase retention of aldehydes and oxygenated monoterpenoids
compared to pasteurization, sterilization, and fresh juice (P 0.05). Pennywort juice flavor components such as
aldehyde group (Table 1) may be lost or transformed during heating.
Moreover, pentanal and hexanal might be formed by autooxidation
and enzymatic oxidation (Hashizume 2007).
Acyclic alcohols were lost after heat treatment. Five alcohols
were found in high abundance in HPP. These compoundsmight be
formed during sample preparation because no action was taken to
inactivate enzymes prior to extraction in this study. Some aldehydes
had significantly decreased concentration or disappeared after
the thermal treatment (P > 0.05), whereas hexanal was found in
sterilized samples at apparently high concentrations than in HPP
juices, which suggests formation by autooxidation.
α-Terpineol (an oxygenated monoterpene) is considered to be
desirable in many fruits, whereas in others it is perceived as an
off-flavor (terpentine-like) (Dung and others 1995). It is known to
be formed in citrus juices from limonene and linalool by acidcatalyzed
reactions (Haleva-Toledo and others 1999). Rui and others
(2007) reported isomerization of linalool and dehydration to