Extraction of FFAs from the microalga N. gaditana FFAs
from the microalga N. gaditana were extracted by the procedure
shown in Fig. 1, which is an adaptation to this microalga of a similar
process applied to the microalgae Phaeodactylum tricornutum (11)
and Isochrysis galbana (13). By this procedure 83.4 3.1 wt% of
fatty acids contained in the microalgal biomass were recovered
and these FFAs were extracted with 73.5 2.6 wt% purity. On the
other hand, saponifiable lipids (SLs) without transforming in FFAs
were also extracted in our laboratory by a similar two-step
process: (i) extraction of lipid from the wet microalgal biomass
with ethanol (96% v/v) and (ii) purification of these extracted
lipids by a second extraction with hexane. This method achieved
a similar SL recovery yield (85%), but the SL purity was only 31%,
the impurities consisting mainly of unsaponifiable lipids
(carotenoids), which obviously can not be transformed into
methyl esters (biodiesel). The transformation of SLs into FFAs by
direct saponification in the biomass (Fig. 1) allows easier
separation of FFAs and unsaponifiable lipids, and, therefore, a
higher purity of the final biodiesel. Besides, the extraction of SLs
as FFAs does not imply an excessive increasing of the economical
cost because only an alkali, as NaOH or KOH, have to be added to
the extraction solvent (ethanol) to transform SLs to FFAs.