Effect of microalga preconditioning on supercritical CO2 ... - ISSF 2012

y (mg astaxantina/gr <strong>microalga</strong>)
12
10
8
6
4
2
550, 70
450, 70
350,70
550, 40
450,40
350, 40
0
0 1 2 3 4 5 6
F (kg de CO2/ g <strong>microalga</strong>)
Figure 2. Cumulative extraction curves <strong>of</strong> aqueous Haematococcus pluvialis homogenate samples as a function <strong>of</strong> extraction
temperature and pressure.
effect <strong>of</strong> the water layer that is not very soluble in scCO2 and may retard extraction. Water is extracted, however,
and its removal can explain the subsequent increase in extraction rate following the initial lag period. Dry
pockets may have developed during extraction that exposed H. pluvialis to scCO2 and facilitated removal <strong>of</strong>
astaxanthin and other components <strong>of</strong> the extract [12]. Following the initial lag period, as water is being removed
from homogenates, the extraction rate remains approximately constant, which suggest that this process is
solubility-controlled. A comparison <strong>of</strong> operational solubilities (Table 2), defined as the slope <strong>of</strong> cumulative
extraction curves in Figure 1 and Figure 2 in the zones where the extraction rate is constant, shows that this is
much higher when extracting dried powder than aqueous homogenate samples. This highlights the negative
effect <strong>of</strong> water on the solubility <strong>of</strong> the lipidic (hydrophobic) components <strong>of</strong> H. pluvialis extract.
Table 2. Operational solubility <strong>of</strong> astaxanthin in supercritical CO 2 (mg/kg) as a function <strong>of</strong> extraction conditions.
Temperature Pressure Operational solubility
(ºC) (MPa) Dry powder Homogenate
40 35 14 1,3
40 45 19 1,6
40 75 36 1,7
70 35 17 1,6
70 45 33 1,8
70 75 65 1,5
Astaxanthin concentration in the extracts <strong>of</strong> aqueous homogenate samples depended also strongly on extraction
conditions (Table 1). In this case, the purity <strong>of</strong> extracts decreased with extraction temperature and was the
highest at an intermediate pressure <strong>of</strong> 45 MPa. Furthermore, the extraction <strong>of</strong> homogenates allowed higher