The results obtained in this study indicate that each factor of
ultrasonic treatment significantly influenced the extraction yield
of all-trans-lycopene from red grapefruit under ultrasound-assisted
extraction. The extraction efficiency was shown to be a function
of time, temperature, solvent/material ratio, ultrasonic
intensity and duty cycle. In comparison with CSE, ultrasound
incredibly reduced the processing time and largely enhanced the
extraction yield. The relatively low temperature under UAE had a
positive effect on lycopene yield and could limit the degradation
of all-trans-lycopene during extraction. An optimal solvent/material
ratio could be adopted for moderating solvent consumption.
Proper ultrasonic intensity was necessary to optimize the extraction
yield. Pulsed ultrasound at certain intervals could be more
efficient than continuous sonication with the advantage of saving
electrical energy. Although these findings demonstrate that the
use of ultrasonic offers considerable advantages on lycopene yield,
low extraction efficiency and degradation of all-trans-lycopene
could occur if conditions of UAE are not optimized. Isomerisation
reaction of lycopene was observed during the process of ultrasound-assisted
extraction and the isomers were analyzed and
identified by means of HPLC-PAD. Therefore, more attention
should be invested in the application of ultrasound technique for
lycopene extraction. The present study provides very useful information
for optimizing ultrasonic extraction conditions of lycopene
from red grapefruit according to the various factors studied. A new
method to make isomers of lycopene was also discovered.