The modern solvent-based oil extraction process usually consists
of extraction by successive countercurrent extractions with
hexane of the previously mechanically ruptured oleaginous material
(Rosenthal et al., 1996). Due to many concerns regarding food
safety when applying hexane in food processing technologies its
use decreased drastically over the years. Hence it is important, that
for newly developed oil-processing technologies the use of hexane
is minimised or possibly even completely avoided. Although in this
study the use of hexane was not completely avoided due to the
need of high purity oil for analysis, for large scale application of
SubWE the separation of the water and oil phase would probably
be sufficient just by using centrifugation (Rosenthal et al., 1996).
The subcritical water extraction (SubWE) kinetics of sunflower
oil and the comparison to extraction kinetic curve obtained by
Soxhlet extraction are presented in Fig. 1a. Results show that for
the SubWE the highest oil yields (gOE) are achieved at an extraction
temperature (Te) of 130 C and a material to solvent ratio (M/S) of
1/20 g/mL, with a maximum yield of 44.3 ± 0.3% after 30 min of
extraction, giving comparable results to those obtained after 4 h
by the Soxhlet (46.2 ± 0.7%). At 160 C a similar maximum
(43.9 ± 0.3%) is achieved for SubWE but after 2 h of extraction. At
other applied temperatures and M/S ratios lower yields are
obtained. Increasing temperature hence improves the extraction
yield of SubWE as was predicted. It can be also observed that at
all conditions investigated, except at 160 C, the extraction rates
are much higher compared to Soxhlet extraction. The highest oil
yields are obtained in te 6 30 min, while in the case of Soxhlet
extraction the time needed is 4 h.