Although it would be expected that increasing temperature
would have a direct positive effect on extraction yield due to
higher solubility of non-polar phase, the slower extraction kinetics
at 160 C can be explained with lower solubility of protein phase at
the applied temperature. In the detailed review by Rosenthal et al.
(1996) it was reported that the amount of oil obtained from oil
seeds using water as extraction medium depends mostly from
the amount of cotyledon cell wall rupture which is done by either
flaking or grounding of seeds. Cotyledon cells present in sunflower
(and many other) seeds contain most of the oil and protein phase
present within the seed, of which the protein phase enclaves the
oil. Rupturing the protein structure or its removal by extraction
is therefore essential for high extraction yields of oil, since oil is
then allowed to diffuse into the extraction medium. At 160 C
the dielectric constant of SubCW is approximately 42 and at
130 C it is approximately 49, which seems to decrease the ability
of the medium to extract the protein phase, consequently not
allowing more oil to be released. Based on these observations, further
increase in Te could therefore have a negative effect on extraction
kinetics. On the other hand, higher temperature would result
in more protein structure rupture, which in this case would have
the same positive effect on the oil yield but at the same time could
cause more structural damage to the other components in the
material.