Fig. 2 shows the percent of oil extraction as a function of time at
ultrasound treatment at pH = 12, temperature of 45 C, agitation
speed of 800 rpm, agitation time of 15 min and ultrasound treatment
temperature of 25 C t. The results showed, in the range of
ultrasonic treatment time 15–90 min, rice bran oil yield increase
rapidly with the treatment time. The improvement was slow in
the 15–70 min and decreased as more than 70 min. Due to the
ultrasonic processing, the reaction process was strengthened
rapidly in a certain period of time. But while the time was too long,
the response would reverse, so that reaction system state to emulsify.
‘‘Cavitation effect” would weaken or even disappear at this
time, so the rate of oil could reduce. The optimum extraction time
of 70 min was selected for ultrasound-assisted extraction of oil
from rice bran.