3.4. One-pot conversion of grease to biodiesel (FAME) with dry cells of
recombinant E. coli strain containing tandem lipases
To further increase the FAME yield, the dry cells of the recombinant
E. coli (Calb/Tll) containing the tandem lipases were used as
the catalysts (4 wt%) for biotransformation of grease. As shown
in Fig. 4, the FFA content decreased with time. In such a system,
no hydrolysis of glyceride happened. In the first 6 h, 7.7 wt% FFA
were converted to FAME via esterification, and 9.3% of the total
17% FAME yield was contributed by the transesterification of glyceride.
At 12 h, the FAME yield reached 60%, and the transesterification
was much faster than the esterification from 6 to 12 h. Both
reactions became slower from 12 to 48 h, and FAME yield increased
to 93% and the FFA content reduced to 1.1% at 48 h. Reaction
for additional 24 h improved the FAME yield to 95%, which is
better than that of result obtained by using wet cells (87% yield).
These results are excellent and provide with the efficient and economical
production of biodiesel from grease. In comparison with
our previous work (Li et al., 2012), the efficiency for using this
whole-cell biocatalyst is much higher, high FAME yield (95%) can
be achieved with less catalyst (4 wt% vs 8 wt%) loading and shorter
reaction time (48 h vs 72 h).