Prior to oil extraction, the yeast cells were broken by homogenization
at 4 C under 800 bar pressure in a high pressure homogenizer
(GEA, Italy). Five passages were taken and reduction in OD
was measured at various passages. Typically, the initial OD of
190 was reduced to 71 after five passages.
The oil extraction from yeast cells was carried out in 50 L SS agitator
tank using a modified method described by Markham et al.
The homogenized cells (5 L) were mixed with 10 L n-hexane
and stirred for 1 h at 950 rpm. The mixture was allowed to stabilize
for 10–12 h at ambient temperature. The bottom aqueous layer
was removed; isopropyl alcohol (IPA) (2.5 L) was added to separate
the organic layer which was subsequently collected and concentrated
to recover oil.
Jatropha oil was obtained by extracting crushed Jatropha curcas
seeds with petroleum ether in a Soxhlet apparatus.
For determining the oil composition, the fatty acids in the oil
were first converted to their methyl esters by trans-esterification
reaction in the presence of the catalyst boron trifluoride [26]. The
fatty acid methyl esters (FAMEs) were then analyzed by GC.
The yeast oil was refined as described [18] and trans-esterified
to biodiesel with 30% sodium methylate at 60–65 C for 2 h. The
lower glycerol layer was removed and crude biodiesel was subjected
to hot water washes to remove soap and impurities. Characterization
of biodiesel was done by GC analysis. Fuel properties of
the methyl ester were evaluated according to standard methods:
Acid value (EN 14104), density (EN ISO 3675), kinematic viscosity
(EN ISO 3104), iodine value (EN 14111) and sulfated ash